Vesuvius, Campi Flegrei, and Campanian Volcanism [1 ed.] 0128164549, 9780128164549

Table of contents :
VESUVIUS, CAMPI FLEGREI, AND CAMPANIANVOLCANISM
Copyright
Contributors
Acknowledgments
1 - Introduction to Vesuvius, Campi Flegrei, and Campanian Volcanism
2.- The contributions and influence of two Americans, Henry S. Washington and Frank A. Perret, to the study of Italian volcanis ...
Henry Stephens Washington
Introduction
Publications before and including 1906
On some Ischian trachytes, 1896
Italian Petrological Sketches, 1896–97
Some analyses of Italian volcanic rocks I and II, 1899–1900
Cross, Iddings, Pirsson, and Washington, 1902
The Roman Comagmatic Region, 1906
Publications from 1906 to 1912
Publications after joining the Geophysical Laboratory, Carnegie Institution of Washington
Publications 1912 to 1919
Publications 1920–1934
Significance to Italian geology and petrology
Stories and anecdotes
Frank Alvord Perret
Acknowledgments
References
3 - Kinematics of the Tyrrhenian-Apennine system and implications for the origin of the Campanian magmatism
Introduction
Geological setting
The Apennine Chain
The Tyrrhenian Sea
Evolution of the upper plate
Reconstruction of the subducted lower plate
Geometric evolution of the Ligurian-Ionian slab
Methods
Ligurian-Ionian slab evolution
Conclusions and implication on the Campanian magmatism
Acknowledgments
References
4 - Lithosphere structural model of the Campania Plain
Introduction
Regional lithospheric models
The lithosphere–asthenosphere system under the Campania Plain
The geodynamical interpretation of the lithosphere–asthenosphere system model
Crustal structure of the Campania Plain
VS models of the Campania Plain
Conclusions
References
5 - Campania volcanoes: petrology, geochemistry, and geodynamic significance
Introduction
Structural setting of volcanism in the Italian peninsula
A volcanological overview of the Campania Province
Petrology and geochemistry of the Campania volcanoes
Somma–Vesuvio
Campi Flegrei (Phlegraean Fields)
Ischia
Procida
Petrogenesis of Campania magmas
Large regional magma chambers beneath Campania
Compositions of primary melts
Nature of mantle sources and metasomatism
Geodynamic implications
A possible geodynamic scenario
Conclusions
Acknowledgment
References
6 -
Tracing magma evolution at Vesuvius volcano using melt inclusions: a review
Geological background
Magma evolution at Somma–Vesuvius volcano
Melt inclusions
Conclusions
References
7 -
Magmatism of the Phlegrean Volcanic Fields as revealed by melt inclusions
Introduction
Geological outlines of the Phlegrean Volcanic District
Description of melt and fluid inclusions found in the Phlegrean Volcanic District magmas
Melt inclusions in the Phlegrean Volcanic District
Fluid inclusions in the Phlegrean Volcanic District
Insights about Phlegrean Volcanic District using melt inclusions
Discussion on melt inclusion data
Evolution of mafic melts
Significance of more-evolved MIs from the PVD
Concluding summary
Acknowledgments
References
8 - The 39 ka Campanian Ignimbrite eruption: new data on source area in the Campanian Plain
Introduction
Geostructural and geophysical outlines of Campanian Plain
Materials and methods
Geomorphological characteristics of the Campanian Plain
Drilling stratigraphy in the southwestern margin of the Campanian Plain
Methods used to determine the physical–mechanical parameters along vertical profiles defined by drilling
Landscape changes resulting from the areal distribution of 39 ka CI units and 15 ka NYT in the Campanian Plain
Volcanological setting of the Campanian Plain
Stratigraphic features of Campanian Ignimbrite unit-1 and vertical welding patterns in the Giugliano area
Transects of CI unit-1 in the N-CVZ
Relationships between physical properties and welding intensity for Campanian Ignimbrite unit-1
Giugliano area
Other sectors of the northern Campanian volcanic zone
Discussion
The basal breccia
Vertical welding patterns of the intermediate part in the Giugliano area
The upper breccia
The role of topography on Campanian Ignimbrite density current runout and formation of coignimbrite ash fall
Emplacement history of CI unit-1 in N-CVZ
Source of the Campanian Ignimbrite unit-1 ignimbrite
Eruptive mechanisms
Acknowledgments
References
9 -
Effect of paleomorphology on facies distribution of the Campania Ignimbrite in the northern Campania Plain, southern Italy
Introduction
Study area
Geological setting
The Campania Ignimbrite
Methods
Results
Pre-Campania Ignimbrite depositional surface
The Campania Ignimbrite deposits
Discussion
Reconstruction of pre-39 ka Campania Ignimbrite environmental features of the Campania Plain
Proximal and distal facies of Campania Ignimbrite
Conclusive remarks
Acknowledgments
References
10 - Petrogenesis of the Campanian Ignimbrites: a review
Introduction
Summary of Campanian tectonic, thermophysical, and geochemical properties
Tectonic framework
Campanian magmatic system
Campanian deposits
Campanian Volcanic Zone computational petrology
Computational approaches
Selection of recent applications
Eruption triggering mechanisms
Volatile exsolution during fractional crystallization
Volatile exsolution during decompression
Sources of unrest
Long-term patterns
Crustal contamination
Concluding remarks
Acknowledgments
References
11 - The Neapolitan Yellow Tuff eruption as the source of the Campi Flegrei caldera
Introduction
Separate sources for the Campanian Ignimbrite and Neapolitan Yellow Tuff
The Neapolitan Yellow Tuff caldera
Distribution and alteration of the Neapolitan Yellow Tuff
Caldera resurgence
Marine surveys in the Bay of Pozzuoli
Borehole data in the subaerial part of the caldera
Onshore geomorphology of Campi Flegrei
Postcaldera volcanic activity
Discussion
Formation of the Neapolitan Yellow Tuff caldera
Caldera resurgence and intracaldera eruptions
Conclusions
Acknowledgments
References
A: supplementary data
12 -
Space-time evolution of an active volcanic field in an extentional region: the example of the Campania margin (eastern Tyrr ...
Introduction
Tectonics
Volcanism
Link between extensional faulting and volcanism
Space-time evolution of tectonic and volcanic systems
References
13 -
Petrologic experimental data on Vesuvius and Campi Flegrei magmatism: a review
Introduction
Phase equilibrium studies and applications
Mafic magmas–Vesuvius
Evolved Vesuvius magmas
Campi Flegrei
Volatile studies
General Considerations
Vesuvius
Water and CO2
Water and chlorine
Chlorine and sulfur
Fluorine
Campi Flegrei
Water and CO2
Chlorine
Mixed fluids and future needs
Acknowledgments
References
14 - Hydrothermal versus magmatic: geochemical views and clues into the unrest dilemma at Campi Flegrei
Introduction
The origin of the Campi Flegrei caldera hydrothermal system
Fluid geochemistry of the actively degassing area: Solfatara and Pisciarelli fumarole data and interpretations
Geochemistry of the Solfatara–Pisciarelli fumaroles: same data but contrasting interpretations
Thermochemistry of the actively degassing Campi Flegrei caldera hydrothermal system
Discussion
Fumaroles in the structure of the Campi Flegrei caldera hydrothermal system
Geochemical models and unrest
Conclusions and perspectives
Acknowledgments
References
15 - Ground movement (bradyseism) in the Campi Flegrei volcanic area: a review
Introduction
Geologic setting at Campi Flegrei
Volcanism at Campi Flegrei volcanic district
Bradyseism at Campi Flegrei
Models for ground movements at Campi Flegrei
Hydrothermal activity at Campi Flegrei
Thermodynamic model for ground movements at Campi Flegrei
Conclusions
Acknowledgments
References
16 - The holocene marine record of unrest, volcanism, and hydrothermal activity of Campi Flegrei and Somma–Vesuvius
Introduction
Geological setting
Campi Flegrei
Somma–Vesuvius
Data and methods
Volcanic and hydrothermal features off the Naples Bay
Seafloor morphology of Naples Bay
Pozzuoli Bay
Somma–Vesuvius offshore
Montagna bank
Seismic imaging of submerged volcanic, hydrothermal, and sedimentary features
The offshore stratigraphic architecture of the Campi Flegrei caldera
Pyroclastic flow deposits offshore vesuvius: the herculaneum sand waves field
Degassing features and soft-sediment deformation: the diapirs field of montagna bank
Conclusion
Acknowledgments
References
17 - Volcanological risk associated with Vesuvius and Campi Flegrei
Introduction
The eruptive history of Somma–Vesuvius
Flow hazard at vesuvius: The Red Zone of the emergency plan of Italian Department of Civil Protection
Suggestions for some criteria for the definition of Red Zone at Somma–Vesuvius
Campi Flegrei
Are we moving toward a third postcaldera volcanic period at Campi Flegrei?
Implications for hazard at Campi Flegrei
Concluding comments on Somma–Vesuvius and Campi Flegrei red zones
References
Index

Citation preview

VESUVIUS, CAMPI FLEGREI, AND CAMPANIAN VOLCANISM Edited by

BENEDETTO DE VIVO HARVEY E. BELKIN GIUSEPPE ROLANDI

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2020 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-816454-9

For information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Candice Janco Acquisition Editor: Amy Shapiro Editorial Project Manager: Hilary Carr Production Project Manager: Omer Mukthar Cover Designer: Mark Rogers Typeset by TNQ Technologies Front Cover: the image “La Grande Eruzione del Vesuvio del 1767 - The great 1767 Vesuvius eruption” is of the artist Adriana Pignatelli Mangoni

Contributors Harvey E. Belkin Retired, U.S. Geological Survey, Reston, VA, United States

Robert J. Bodnar Fluids Research Laboratory, Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States

Mauro Caccavale Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Sezione di Napoli, Napoli, Italy

Claudia Cannatelli Department of Geology, FCFM, University of Chile, Santiago, Chile; Andean Geothermal Center of Excellence (CEGA), University of Chile, Santiago, Chile

Michael R. Carroll Universita` di Camerino- Scuola di Scienze e Tecnologie, Sezione Geologia, Camerino, Italy

Marta Corradino Dipartimento di Scienze della Terra e del Mare (DiSTeM), Universita` di Palermo, Palermo, Italy

Maria Rosaria Costanzo Department of Earth Sciences, Environment and Resources, University of Naples Federico II, Italy

Giuseppe De Natale Istituto Nazionale di Geofisica e Vulcanologia, sezione di Napoli «Osservatorio Vesuviano», Napoli, Italy

Benedetto De Vivo Pegaso On Line University, Naples, Italy; Adjunct Professor, Dept of Geosciences, Virginia Polytechnic Institute & State University (Virginia Tech), Blacksburg, VA, United States; Nanjing University, Nanjing, China; Hubei Polytechnic University, Huangshi, China

Massimo Di Lascio Consultant, Self-employed Geologist, Battipaglia (Salerno), Naples, Italy

xiv

Contributors

Rosario Esposito University of California, Department of Earth, Planet, and Space Sciences, Los Angeles, CA, United States

Giuseppe Esposito Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Sezione di Napoli, Napoli, Italy

Alessandro Fedele INGVdOsservatorio Vesuviano, Naples, Italy

Sarah Jane Fowler School of Earth Sciences, University of Bristol, Bristol, United Kingdom

Tom Gidwitz South Dartmouth, MA, United States

Christopher R.J. Kilburn University College London, London, United Kingdom

Annamaria Lima Dipartimento di Scienze della Terra, delle Risorse e dell’Ambiente, Universita´ di Napoli Federico II, Naples, Italy

Chiara Macchiavelli Group of Dynamics of the Lithosphere, Institute of Earth Sciences Jaume Almera, Structure and Dynamics of the Earth, Barcelona, Spain

Fabio Matano Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Sezione di Napoli, Napoli, Italy

Alfonsa Milia ISMAR, CNR, Napoli, Italy

Flavia Molisso Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Sezione di Napoli, Napoli, Italy

Roberto Moretti Universite´ de Paris, Institut de Physique du Globe de Paris, CNRS UMR 7154, Paris, France; Observatoire Volcanologique et Sismologique de Guadeloupe, Institut de Physique du Globe de Paris, Gourbeyre, France

Contributors

Concettina Nunziata Department of Earth Sciences, Environment and Resources, University of Naples Federico II, Italy

Giuliano Francesco Panza Emeritus Honorary professor China Earthquake Administration (CEA), Beijing, China; Honorary professor Beijing University of Civil Engineering and Architecture (BUCEA), Beijing, China; Accademia Nazionale dei Lincei & Accademia Nazionale dei XL, Rome, Italy

Salvatore Passaro Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Sezione di Napoli, Napoli, Italy

Angelo Peccerillo Retired from Department of Earth Sciences, University of Perugia, Perugia, Italy

Giulia Penza University of Camerino, School of Science and TechnologydGeology Division, Camerino, MC, Italy

Fabrizio Pepe Dipartimento di Scienze della Terra e del Mare (DiSTeM), Universita` di Palermo, Palermo, Italy

Pietro Paolo Pierantoni University of Camerino, School of Science and TechnologydGeology Division, Camerino, MC, Italy

Giuseppe Rolandi Retired, University Napoli Federico II, Napoli, Italy

Roberto Rolandi Dipartimento Scienze della Terra, Ambiente e Risorse, Universita` di NapoliFederico II, Naples, Italy

Daniela Ruberti Department of Engineering, University of Campania “L. Vanvitelli”, Aversa (Caserta), Italy

Marco Sacchi Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Sezione di Napoli, Napoli, Italy

xv

xvi

Contributors

Antonio Schettino University of Camerino, School of Science and TechnologydGeology Division, Camerino, MC, Italy

Renato Somma INGVdOsservatorio Vesuviano, Naples, Italy

Frank J. Spera Department of Earth Science and Earth Research Institute, University of California, Santa Barbara, CA, United States

Volkhard Spiess Faculty of Geosciences, University of Bremen, Bremen, Germany

Paola Stabile Universita` di Camerino- Scuola di Scienze e Tecnologie, Sezione Geologia, Camerino, Italy

Lena Steinmann Faculty of Geosciences, University of Bremen, Bremen, Germany

Stella Tamburrino Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Sezione di Napoli, Napoli, Italy

Maurizio M. Torrente DST, Universita` del Sannio, Benevento, Italy

Claudia Troise Istituto Nazionale di Geofisica e Vulcanologia, sezione di Napoli «Osservatorio Vesuviano», Napoli, Italy

Eugenio Turco University of Camerino, School of Science and TechnologydGeology Division, Camerino, MC, Italy

Mattia Vallefuoco Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Sezione di Napoli, Napoli, Italy

Guido Ventura Istituto Nazionale di Geofisica e Vulcanologia, INGV, Roma, Italy

Marco Vigliotti Department of Engineering, University of Campania “L. Vanvitelli”, Aversa (Caserta), Italy

Acknowledgments We acknowledge the support of Elsevier B.V. through the process of planning, writing, reviewing, and the production of Vesuvius, Campi Flegrei, and Campanian Volcanism. Behind the Elsevier banner is a staff of extremely competent, hardworking people, without whom the production of this volume would have been far more difficult and of lesser quality. Omer Mukthar Moosa, Mark Rogers, Sheela Bernardine B. Josy, and Amy Shapiro are gratefully thanked. We especially thank Hilary Carr, whose excellent editorship has led and instructed us to the successful completion of this volume. We also thank Adriana Pignatelli Mangoni, Naples, Italy, for the use of her gouache La Grande Eruzione del Vesuvio nel 1767 that appears on the volume’s cover. Lastly, we thank all the chapter authors for their contributions and the many peer reviewers for their suggestions and corrections. Benedetto De Vivo Harvey E. Belkin Giuseppe Rolandi

1 Introduction to Vesuvius, Campi Flegrei, and Campanian Volcanism Benedetto De Vivo,1, 2, 3, 4 Harvey E. Belkin,5 Giuseppe Rolandi6 1

Pegaso On Line University, Naples, Italy; 2Adjunct Professor, Dept of Geosciences, Virginia Polytechnic Institute & State University (Virginia Tech), Blacksburg, VA, United States; 3Nanjing University, Nanjing, China; 4Hubei Polytechnic University, Huangshi, China; 5Retired, U.S. Geological Survey, Reston, VA, United States; 6Retired, University Napoli Federico II, Napoli, Italy

In August of CE 79, Vesuvius was erupting (although, recent archeological research suggests the month was October). In two letters to the Roman historian Tacitus, Pliny the Younger describes the events. The first letter describes the journey of his uncle, Pliny the Elder, during which he perished. Pliny the Elder had received a letter from Rectina, the wife of Tascus, asking to be rescued, but due to the ongoing eruption, the rescue boat could not reach the shore near her home and instead Pliny the Elder sailed to Stabiae to meet Pomponianus where they both died. The second letter by Pliny the Younger describes his observations of the eruption from Misenum, a town in the Pozzuoli Gulf, across the Bay of Naples. These letters are probably the very first detailed description of a volcanic eruption. It is interesting also to note that Pliny the Younger never mentions the towns of Ercolano and Pompeii, so their existence remained unknown until the late 16th century, when they were discovered covered by Mt. Somma pyroclastics. For the next two millennia, scientists, clergy, travelers, politicians, ambassadors, and others have written thousands of papers, books, and other documents on the volcanoes and volcanism in the Naples region that includes Mt. SommaeVesuvius, Campi Flegrei (CF), the Island of Ischia, and related rocks. Thus, it would be reasonable to assume that “all the questions have been asked, and all the answers have been given” regarding the science of the Vesuvius, Campi Flegrei, and Campanian Volcanism. https://doi.org/10.1016/B978-0-12-816454-9.00001-8 Copyright © 2020 Elsevier Inc. All rights reserved.

1

2

Chapter 1 Introduction to Vesuvius, Campi Flegrei, and Campanian Volcanism

Neapolitan volcanic region. Unfortunately, the reality is just the opposite! The geology and geophysics of the Neapolitan volcanic region are very complexdthe tectonics, the petrology, the lithospheric structure beneath the volcanic systems, and many other geological and geophysical aspects. After nearly 2000 years of research, the following three questions cannot be answered with any confidence: will there be another volcanic eruption in the Naples area, and if so, where, and when? Answers to these questions do not have just academic interest, as there are more than three million people living in the Neapolitan volcanic region. In the Repubblica Italiana, the Department of Civil Protection is given the very important and difficult task of preparing volcanic risk maps, zoning, and other aspects related to the potential of a volcanic eruption. The risk maps, zoning, etc., must be continuously updated as new geologic information and research becomes available. For one thing is absolutely certain that during a volcanic eruption, the lava, pyroclastic flow, ash cloud, etc., will not obey any political boundaries or preconceived scenarios. With this book on the volcanism of the Neapolitan region (Vesuvius, CF, and ignimbrites in the Campanian plain), we hope that the scientific points of views of different authors are not interpreted as “certainties”. Some of the chapters highlight ongoing controversial subjects related to the volcanism of the Neapolitan volcanic region, such as the source of the 39 ka Campanian Ignimbrite (CI), the significance of the bradyseism in CF, the nature of the Neapolitan Yellow Tuff (NYT) eruption, and the delineation of volcanic hazard zones for civil protection. Such controversy is a very healthy part of scientific progress as it forces all the involved scientists to reexamine their data, assumptions, and hypotheses. The literature is filled with rejected or modified theories as new data were collected and examined. What we consider important is that whatever the real scenario, in the short and long term, for Vesuvius, CF, and ignimbrites in the Campanian plain, the results are obtained only if there is a nondogmatic approach, which favors an impartial and balanced evaluation of peer-reviewed research. This, unfortunately, has often not been the case in Italy in recent years, especially due to an overly tight and unhealthy link between politics and various research groups. These links do not benefit science or the society that supports it. This dogmatic approach is especially egregious if decisions regarding the public safety and security are made using biased or poorly evaluated scientific research. We hope that these chapters will enable researchers to study the controversial issues

Chapter 1 Introduction to Vesuvius, Campi Flegrei, and Campanian Volcanism

of the Campanian Plain volcanism for the benefit of science and people living around the metropolitan area of Naples. Sixteen chapters in this volume have been selected to give the reader an idea of the current “state of the art” regarding the various aspects of geology and geophysics related to the Neapolitan volcanic region. A short summary of each chapter by the different authors is given below: Chapter 2: Belkin and Gidwitz (The contributions and influence of two Americans, Henry S. Washington and Frank A. Perret, to the study of Italian volcanism with emphasis on volcanoes in the Naples area) report the work, significance, and influence, one century ago, of two American researchers, Henry Stephens Washington and Frank Alvord Perret, in Italian volcanism with emphasis on Neapolitan volcanoes. Both Washington and Perret made significant contributions to the geology, petrology, and volcanology of Italy, in general, but in particular to the Vesuvius, CF (Phlegraean Fields), and the Island of Ischia. Both, from the East Coast of the United States, published classical works on Italian volcanoes, the Roman Comagmatic Region and the Vesuvius Eruption of 1906, published by the Carnegie Institution of Washington. Chapter 3: Pierantoni et al. (Kinematics of the TyrrhenianApennine system and implications for the origin of the Campanian magmatism) make a reconstruction of the geodynamic evolution of the Italian peninsula to understand the processes, which allowed the formation of the magma following the geometry of the LigurianeIonian slab. In their reconstruction, the Campanian Plain is located above a singular asthenospheric window, created by the Ionian slab detachment, which determines, during the Upper Pleistocene, an elastic rebound of the Apulian continental lithosphere. The consequent mantle upwelling gives rise to the huge amount of magma that characterizes the Campanian Plain. Chapter 4: Nunziata et al. (Lithosphere structural model of the Campania Plain) discuss the lithosphere structural model of the Campania Plain. According the authors, a mantle wedge (VS of about 4.2 km/s), 50 km thick, is found at depths shallower than 30 km, on the top of the westward subducting Apenninic lithosphere, overlying two faster layers (VS of about 4.4 km/s) up to about 300 km of depth. This is compatible with buried huge amounts (more than 1.5 km) of calc-alkaline andesitic and basaltic lavas and with the geochemical and petrological findings that subduction-related magmas, with broadly trachybasaltic compositions, were parental to all the volcanic suites in Campania. A main feature in the upper crust is the low VS layer (5% velocity reduction) that starts at about 14e15 km of depth and reaches the Moho. The low-velocity crustal layer seems to be a

3

4

Chapter 1 Introduction to Vesuvius, Campi Flegrei, and Campanian Volcanism

regional feature as it has been found below Roccamonfina in the north and CF, Bay of Naples, and Mt. Vesuvius in the south. The widespread presence of such layer, with the percentage of velocity reduction peaking below the CF District and Mt. Vesuvius, seems to be consistent with the presence of an extended reservoir, fed from a deep source located in the upper mantle, from which the pockets of magma may rise to shallower depths. Chapter 5: Peccerillo (Campania volcanoes: petrology, geochemistry and geodynamic significance) discuss the petrology, geochemistry, and geodynamics of the Campania Magmatic Provincedincluding SommaeVesuvius, CF, and Ischia and Procida islandsdwhich is petrologically and geochemically distinct from the Roman province, but with close similarities with Stromboli volcano, in eastern Aeolian arc, suggesting that the Campania volcanoes do not represent the southern extension of the Roman province, but rather the northern end of the Aeolian arc. Both the Campania and Stromboli parental magmas were generated from a mantle source that was affected by metasomatic modifications by fluids coming from the subducting Ionian oceanic slab and associated sediments. The ocean island basaltetype component of the eastern Aeolian and Campania volcanoes was provided by mantle inflow from the foreland. Asthenospheric mantle migration took place through a slab window formed by along-strike tear-off of the Ionian-subducting lithosphere and was favored by suctioning by the slab sinking and rollback toward the southeast. Chapter 6: Cannatelli (Tracing magma evolution at Vesuvius volcano using melt inclusions: a review) traces evolution of SommaeVesuvius, making a review of melt inclusion (MI) studies. In the last few decades, the volcanic complex has served as a natural open laboratory, where scientists have applied different analytical techniques (geophysical and geochemical) to unravel the nature and evolution of magmas, the location and structure of magma storage, the effect of volatile on determining frequency, and the style of eruptions. Cannatelli presents the major findings and existing knowledge about a geochemical tool that, in the last few decades, has been used to understand volcanic behavior and nature: MIs. In particular, the author focuses on the use of MIs as a tracer for magma geochemical composition and evolution at SommaeVesuvius and recompiles all the available MI data previously published in the literature. Chapter 7: Esposito (Magmatism of the Phlegrean Volcanic Fields as revealed by melt inclusions), to answer questions on the evolution and source of the CF magmatism, uses as investigative tool MIs. Esposito compares the MI data from the literature related to CF, Procida, and Ischia and he highlights three main

Chapter 1 Introduction to Vesuvius, Campi Flegrei, and Campanian Volcanism

points based on this comparison. The first is that only a few MI show quasiprimitive composition, and these can be compared to investigate the magma sources below the three different localities of the Phlegrean Volcanic District (PVD), highlighting that the same magma source could be present below the three localities of the PVD at different times. The second point is that some of the more evolved MIs show divergence from the bulk rock trend, indicating a natural reheating before eruptions, driven either by hotter magma recharging or by crystal settling. The third point is that many MI in the literature are showed as bubble-bearing, not taking into account the volatile contents of bubbles, thus indicating that more research is needed to corroborate or discredit advanced interpretations of preeruptive volatile contents based on MIs. Chapter 8: Rolandi et al. (The 39 ka Campanian Ignimbrite eruption: New data on source area in the Campanian Plain), based on new drillings through the Campanian Plain, report that the CI is composed of two 39 ka depositional units, clearly distinguished by their areal distribution and welding characteristics: CI Unit-1 at the base, covered in some areas by CI Unit-2. The CI Unit-1 is the most extensive gray tuff deposit showing an unusual degree of welding within the southwestern sectordGiugliano areadof the Campania Plain, which is never found in the ignimbritic deposits in other areas of the Plain. The absence of a caldera in the Giugliano area indicates that the CI source is associated with one or more regional tectonic structures. Probably, this source area was extended to the south, but it was not related to the Campi Flegrei caldera (CFc) as assumed by other authors. From the Giugliano area, the coignimbrite expanding gas increased strongly, following a long runout over the flat topography of the Campanian Plain and by impacting, in the north and east, the Apennine and Roccamonfina reliefs. Chapter 9: Ruberti et al. (Effects of the palaeomorphology on facies distribution of the Campanian Ignimbrite in the northern Campania Plain, southern Italy) discuss the effects of palaeomorphology on facies distribution of the CI (39 ka), one of the most explosive eruptions in the last 200 ka in Europe. The pyroclastic deposits associated to this event show different lithofacies from the vent to the medial distal part reflecting changes in style of deposition and/or palaeoenvironmental setting. Based on about 1000 well log stratigraphies and previous studies, a qualitative restoration was made of the pre-39 ka CI eruption palaeomorphology of the Campania Plain, where four main paleogeographic domains are recognized, conditioning the medial/distal distribution of the lithofacies across the plain and their volcanoclastic characteristics.

5

6

Chapter 1 Introduction to Vesuvius, Campi Flegrei, and Campanian Volcanism

Chapter 10: Fowler (Petrogenesis of the Campanian Ignimbrites: a review) reviews intensive research results over the past two centuries based on tectonic, geochemical, and thermophysical database within the Campanian Volcanic Zone, particularly with regard to the voluminous 39.28  0.11 ka CI. New observations on pre- and post-CI deposits provide a basis for identifying long-term petrogenetic patterns. The review summarizing different aspects of Campanian Volcanic Zone research highlights major advances, providing a foundation on which to test hypotheses and construct quantitatively constrained predictions. The importance of fractional crystallization and open-system mechanisms including magma mixing and assimilation during magma evolution is emphasized. Chapter 11: Rolandi et al. (The Neapolitan Yellow Tuff eruption as the source of the Campi Flegrei caldera) present an analysis of the CF, formed inside a 12  16 km caldera system as a result of the 15 ka NYT eruption, which produced about 50 km3 of trachytic magma. Caldera collapse developed within a regional tectonic extensional regime, where local faults mirror regional fault trends. The result was complex caldera architecture, indicated by multiple features attributable to the interaction between trapdoor and downsag geometries. The authors present geological and volcanological constraints to propose an evolutionary sequence model whereby the NYT is an isolated volcanic structure that formed only in response to a single 15 ka eruption, in contrast to some previous theories. Chapter 12: Milia and Torrente (Space-time evolution of an active volcanic field in an extended region: the example of the Campania Margin, eastern Tyrrhenian Sea) discuss results of their study investigating offshore and onshore areas of the Campania Margin in terms of stratigraphy, tectonics, and volcanism at a regional scale, not focusing their research works at explaining the relationships between tectonic and volcanism on a single volcano or eruption. The authors documented and reconstructed the 3D geometry of several buried volcanoes and volcanoclastic deposits and recognized a complex late Quaternary tectonic evolution of the region. These results suggest a strict genetic link between rifting and volcanic activity in terms of space-time evolution and that high volumes of magma rose to the surface through regional faults. Chapter 13: Stabile and Carroll (Petrologic experimental data on Vesuvius and Campi Flegrei magmatism: a review) discuss experimental studies of compositions relevant to magmatism at Vesuvius and CF, as they provide constraints on the pressure, temperature, and magmatic volatile activities prevailing during

Chapter 1 Introduction to Vesuvius, Campi Flegrei, and Campanian Volcanism

various phases of eruption. Such information helps to define pressures (depths) of origin for some well-studied eruptions and differentiation trends that link magma compositions potentially related by crystal-liquid differentiation processes. Likewise, studies of volatile solubility in the relatively alkali-rich melt composition characteristic of Vesuvius and CF magmatism can provide valuable constraints for interpreting the composition of MIs in phenocrysts of many eruptive products. The authors discuss how these experimental data can help to explain pressures of MI entrapment, the possible importance of hydrosaline brines in some magmas, and degassing processes or CO2 fluxing experienced by melt compositions preserved in MIs. Chapter 14: Moretti et al. (Hydrothermal vs. Magmatic: Geochemical views and clues into the unrest dilemma at Campi Flegrei), based on the geochemical data recorded at CFc in the last 35ka, review the two main approaches appearing in the literature, yielding diametrically opposite conclusions when comparing the 1982e84 and ongoing (post-2000) CFc unrest episodes. The authors show that inert gases help to evaluate the geochemical signature of the deep upwelling gas, not compatible with a magma migrating to shallow depths in recent times. After the exhaustion of the volatile content of the shallow magma emplaced in 1982e84, only the deep-sourced (8 km) magmatic gas feeds and heats the present-day hydrothermal system. The authors establish that the nature of the 1982e84 unrest was magmatic, due to the emplacement of a shallow (3e4 km deep) magma, interfering with the “normal” degassing dynamics from the deep (8 km) magmatic reservoir of regional size. On the contrary, the post-2005 unrest is unlikely magmatic and most likely hydrothermal. The discussed scenarios confirm in all cases, and independently of the type of unrest, the strong role played by the CO2-rich gas release of deep provenance. Chapter 15: Cannatelli et al. (Ground movement (bradyseism) in the Campi Flegrei volcanic area: a review), after illustrating the CF volcanic evolution, discuss the different theories and interpretation of the ground movements (bradyseism) phenomenon periodically occurring in one of the highest risk volcanic areas on Earth and one of the most densely populated volcanically active areas in the world. The active caldera of CF, located just west of the city of Naples, has been known since Roman times for its hydrothermal activity, intense volcanism, and slow, vertical ground movements, called bradyseism. In their contributions, the authors provide a detailed review of the several models proposed in the past 40 years to explain ground movements at CF. Although several authors propose that the driving mechanism for the

7

8

Chapter 1 Introduction to Vesuvius, Campi Flegrei, and Campanian Volcanism

accelerated ground uplift at CF can be attributed to an emplacement of magma at shallow depth, no scientific (petrological, geochemical, or geophysical) evidence seems to support this hypothesis. The authors suggest, in contrast with other models, that a hydrothermal model without magmatic recharge paints a better picture of the bradyseism phenomenon, as it better links scientific data available in the literature with the magmatic-hydrothermal processes at CF. Chapter 16: Sacchi et al. (The Holocene marine record of unrest, volcanism and hydrothermal activity of Campi Flegrei and SommaeVesuvius) document the marine record of a spectrum of volcanic, hydrothermal, and sedimentary features that characterize the latest PleistoceneeHolocene evolution of the Naples Bay offshore CF and SommaeVesuvius. The authors results are based on the integrated analysis of high-resolution marine digital terrain models derived from swath bathymetry surveys and high-resolution reflection seismic profiles calibrated with marine gravity core data. Between the SommaeVesuvius and Pozzuoli Bay, seismic profiles calibrated with gravity core data revealed the occurrence of a hummocky seafloor region, known as Banco della Montagna (i.e., the Montagna Bank). This volcanic bank was shaped by the dragging and rising up of volcanoclastic diapirs (mostly unconsolidated pumice) as a consequence of pore fluid overpressure at depth and associated active fluid venting at the seafloor. Chapter 17: De Vivo and Rolandi (Hazard assessment on Vesuvius and Campi Flegrei active volcanic areas: A critical review and alternative views) suggest that the eruptive history of SommaeVesuvius and CF gives reasonable reasons to expect eruptions in the future, and they critically discuss the effectiveness of the present delimitation of the Red Zones of both volcanic active areas carried out by the Italian Department of Civil Protection and present their alternative views. The authors believe that both the risk assessment models expounded by DCP do not use the best scientific data for estimating the areas and levels of risk that could be associated with the next probable worst-case scenario eruptions, both at SommaeVesuvius and CF.

2 The contributions and influence of two Americans, Henry S. Washington and Frank A. Perret, to the study of Italian volcanism with emphasis on volcanoes in the Naples area Harvey E. Belkin,1 Tom Gidwitz2 1 2

Retired, U.S. Geological Survey, Reston, VA, United States; South Dartmouth, MA, United States

Henry Stephens Washington Introduction Henry Stephens Washington, the son of George and Eleanor P. (Stephens) Washington, was born in Newark, New Jersey, on January 15, 1867. His family was well-to-do, related to that of George Washington, and he grew up on a homestead in Locust, New Jersey, a few kilometers from the Atlantic shore. At age 12, he had his own chemistry laboratory, and at age 15, he entered Yale College, where he received his A.B. degree with special honors in physics and natural science. Washington continued at Yale and received an A.M. in 1888. As a graduate assistant in physics, he studied mineralogy and petrography. An early published work involved a crystallographical and optical study of copper minerals under the direction of Prof. E. S. Dana in collaboration with W.F. Hillebrand of the US Geological Survey (USGS) (Hillebrand and Washington, 1888). After Yale, he attended the American School of Classical Studies at Athens, Greece, and participated in various archeological excavations with his brother Charles M. Washington. In 1891, Washington enrolled at Universität Leipzig with Professors F. Zirkel and Vesuvius, Campi Flegrei, and Campanian Volcanism. https://doi.org/10.1016/B978-0-12-816454-9.00002-X Copyright © 2020 Elsevier Inc. All rights reserved.

9

10

Chapter 2 The contributions and influence of two Americans

C.H. Credner for petrographic and geologic studies leading to a PhD with highest honors in 1893. For his PhD he studied a group of volcanoes in what is now eastern Turkey (Washington, 1894a). In 1895, he returned to Yale to study rock and mineral chemical analysis under the guidance of Professor Louis V. Pirsson. Using Pirsson’s techniques as a basis, Washington equipped his own laboratory at his boyhood home in Locust, New Jersey. Now in an independent position, he could collect, petrographically describe, and analyze any rock he collected; some of the first rocks he analyzed were those he collected in Italy (Merwin, 1952). From the 1890s until his death in 1934, Washington produced a prodigious volume of scientific work encompassing geology, petrology, mineralogy, chemistry, and archeology (e.g., Keyes, 1934; Merwin, 1952; Milton, 1991). He was interested in archeology throughout his life and continued to publish on its various aspects especially related to mineralogy and rock chemistry (e.g., Waldstein and Washington, 1891; Washington, 1894b, 1898, 1921, 1922). For more details concerning his life, the reader should consult stories, memorials, and obituaries by Keyes (1934), Fenner (1934), Lewes (1935), Barth (1936), Spencer (1936), Merwin (1952), Gibson (1983), and Milton (1991). Milton (1991) describes three phases in Washington’s life, centered on his wife running off with an Englishman, and a failed investment in Brazilian diamonds (cf. Gibson, 1983). Thus, in light of this reversal of fortune, Washington became a consulting mining geologist with a New York City office from 1906 to 1912. During this interval, his basic research was curtailed. In 1912, he joined the Geophysical Laboratory, Carnegie Institution of Washington. The general structure of this chapter section will use these three periods to describe his research in the form of commentary on his relevant publications. This chapter section is concerned with Washington’s contributions related to the petrology and mineralogy of Italy, with particular emphasis on the volcanic region around Naples, Italy, including Mt. SommaeVesuvius, Campi Flegrei (Phlegraean Fields), and the Island of Ischia. Washington was principally a petrologist interested in rock chemistry and mineralogy, but he also included detailed geographic and geologic descriptions of the research regions to place his geochemical, mineralogical, and petrological data in the proper context. After the publication of The Roman Comagmatic Region in 1906, Washington did not study, in detail, the volcanoes around Naples, but studied many other Italian volcanic regions. These studies will be briefly summarized to show the significance of

Chapter 2 The contributions and influence of two Americans

Washington’s research to the petrological and mineralogical knowledge of Italian geology. Some publications cited were translated or abstracted into Italian; these are not discussed.

Publications before and including 1906 On some Ischian trachytes, 1896 In the Fall of 1894, Washington visited the volcanic Island of Ischia, about 30 km southwest of Naples in the Gulf of Naples, southern Italy, to collect representative specimens for study. During petrographic examination of thin sections, Washington (1896a) observed sheaf-like bundles of feldspar crystals from samples collected from Mt. Rotaro that he found interesting enough to publish a short descriptive paper on them before a more detailed text (see Some Analyses of Italian Volcanic Rocks I section). He spent much text discussing the origin of these spherulites and compares their shape and texture with many similar references in the literature.

Italian Petrological Sketches, 1896e97 In 1896e1897, the Journal of Geology published five long papers (Washington, 1896b,c; 1897a,b,c) on four Italian volcanic areas plus a summary and conclusions: 1dThe Bolsena Region, 2dThe Viterbo Region, 3dThe Bracciano, Cerveteri, and Tolfa Regions, 4dThe Rocca Monfina Region (note that name is now Roccamonfina in today’s literature), and 5dSummary and Conclusion. In Sketch 1, Washington describes his trip to Italy in 1894, visiting the Italian volcanic areas and collecting representative samples for petrographic examination and chemical analysis. As he explains: The number and easy accessibility of its volcanoes render Italy an enticing field for the geologist. The peculiar characters of their eruptive rocks, which are rich in potash, and in which leucite is a most common mineral, render them of special interest to the petrologist. It would seem, however, judging from a quite extensive survey of the literature, that the country has been rather neglected in recent years by petrologists; since, except for a comparatively small number of modern papers describing limited districts, we must turn for many of our descriptions to the writers of more than a quarter of a century ago. Few attempts also have been made to correlate the facts in our possession for the purpose of determining the general petrological characters of the Italian province.

11

12

Chapter 2 The contributions and influence of two Americans

The organization in each of the four Regional Sketches is as follows: (1) BibliographydWashington reviews all the references known to him, but only discusses the more recent papers relevant to each region, (2) TopographydA detailed description, including latitude and longitude, is given, (3) PetrographydAn extensive discussion of all the rock types Washington identified in his collection and reference to those described by others, but not collected by him. Thin sections were prepared and detailed descriptions of the mineralogy are given, and (4) Chemical CompositiondTables are presented that give rock analyses from the literature that Washington had deemed worthy, plus a few he analyzed personally. In the last Sketch, Washington concludes that what he has studied, from Bolsena to the Campanian volcanoes, constitutes a “petrographical province” characterized chemically by low to moderate silica and high K2O and petrographically by the abundance of leucite in many rock types. His discussion of the Campanian volcanoes is limited to the recognition that Vesuvius is different from both Ischia and Campi Flegrei, and the latter have abundant trachyte, in contrast to most of the northern volcanoes he examined.

Some analyses of Italian volcanic rocks I and II, 1899e1900 In two papers, Washington (1899, 1900) publishes the results of his rock analyses and mineralogical studies on rocks collected and described in his Italian Petrological Sketches. He states his reasons: During the past two years I have made a number of analyses of Italian volcanic rocks, with the intention of incorporating them in a general article on the subject. As, however, other work has come up which will delay this indefinitely, it has been decided to publish them. Isolated analyses of rocks, without discussion of their relations to those of other connected types, are of little use. But they may prove of service to others investigating this region, and personally I would like to clear out this pigeon-hole.

His “pigeonhole” includes analyses of trachytes from the Phlegraean Fields (Campi Flegrei) and the Island of Ischia (Part I); ciminite (latite) from Mt. Cimino, Viterbo, “mica-trachyte” from Mt. Catini, Tuscany, andesite from Radicofani, Tuscany, and leucitite from Capo di Bove, Alban Hills (Part II). In spite of his desire to just present the data without discussion, he does give detailed discussions and comparisons with some of his analyses and mineralogy. Furthermore, he discusses some of his

Chapter 2 The contributions and influence of two Americans

older data in light of more analytical experience and knowledge and “repudiates” a former analysis, explaining the chemical details. The analysis I. Leucitite from Capo di Bove, Washington analyst (Washington, 1900, p. 53), gives K2O ¼ 8.97wt%, w2wt% higher than an 1869 analysis by Bunsen from the same locality shown for comparison. Washington’s data are correct and reflect the modal abundance of leucite [K(AlSi2)O6] in the rock. Spencer (1936) and my petrology professor, S.A. Morse, related that some colleagues during Washington’s time “playfully suggested that tobacco ash accounted for the high percentages of potash in his rock analyses”; a cigar was his constant companion, and he handed one to whomever he met (see Fig. 2.3 below).

Cross, Iddings, Pirsson, and Washington, 1902 Early on in Washington’s study of igneous rocks, he recognized the need for classification and systemization based on accurate rock chemistry, and so did Whitman Cross (USGS), Joseph P. Iddings (USGS), and Louis V. Pirsson (Yale), and together they produced the Cross, Iddings, Pirsson, and Washington (CIPW) norm classification (Cross et al., 1902) that has lasted for more than 100 years, albeit with some modifications. In the 1906 The Roman Comagmatic Region text, Washington presents CIPW norms for all his rock chemical analyses.

The Roman Comagmatic Region, 1906 Washington (1906) published The Roman Comagmatic Region (Fig. 2.1) as an extensive summary, to date, of his fieldwork, petrography, and chemical analyses of volcanics from Lake Bolsena north of Rome, extending southeast to Vesuvius, Ischia Island, and Campi Flegrei at Naples. The Carnegie Institution of Washington, which published the volume, partially sponsored these studies. Here, he not only describes the petrography and chemistry of his extensive collections but also proposes that these volcanoes have a common origin and defines the volcanic region as a “comagmatic region.” Any reader of this volume should be forewarned that Washington uses rock names proposed by Cross et al. (1902) based on chemistry and divided into class, order, rang, and subrang; however, Washington also gives the “old” name, e.g., subrang phlegrose ¼ trachyte, which will be more familiar to the modern reader. He divides the comagmatic region into seven districts: Vulsiniandthe volcanic complex around Lake Bolsena, Ciminiand volcanoes near Viterbo, Sabatiniandthe volcanic complex around

13

14

Chapter 2 The contributions and influence of two Americans

Figure 2.1 Front cover of The Roman Comagmatic Region (Washington, 1906).

Lake Bracciano, Latiandthe Colli Albani complex, Hernicand volcanics in the Saco River area, Auruncandthe Roccamonfina complex, and the Campanian district. The Campanian district comprised three quite distinct centers of activity, Mt. Sommae Vesuvius, Campi Flegrei (Phlegraean Fields), and the Island of Ischia. Washington recognized that the cessation of volcanic activity from north of Rome to Naples shifted southerly, mostly

Chapter 2 The contributions and influence of two Americans

gleaned from historical references before radiometric dating. The last recorded eruption of Ischia was in CE 1302, the last eruption in Campi Flegrei was Monte Nuovo in CE 1538, and recent Vesuvius activity started in CE 1631 and continued to erupt with an average 7-year repose period. About 70% of the text is devoted to “petrography” where he describes in detail, each of his 38 “subrang” Roman comagmatic region rock types. Each description includes Megascopic characters, Microscopic characters, Chemical composition, Mode, Occurrence, and Name. At the end of each rock type discussion, there is a summary of the hand specimen character, microscopy, mineralogy, and what are considered type specimens. In the “Mode” section, the norm is given and compared with the measured mode. The norm, a calculated theoretical mineralogy based on the chemical composition, had only been recently developed (Cross et al., 1902). Washington also gave analyses from other authors from the sample or similar locality. He often commented on their quality and would give a detailed explanation on why some other analyst’s results differ from his determinations. After the extensive petrographic and chemical descriptions, Washington defines the Roman comagmatic region as follows: silica (SiO2) ranges from 45 to 62wt%, but most vary from 56 to 47wt%, alumina (Al2O3) is generally high with a narrow range only from 17 to 20wt%, lime (CaO) is high with a considerable range, and soda (Na2O) tends to be low and varies from 1.0 to 7.2 with most from 1.5 to 3.5wt%. The most distinguishing chemical characteristic of this comagmatic province is the high potash (K2O) content that ranges from 3.7 to 11.3wt% with the majority only from 6.4 to 9.6wt%dit is indeed a “potassic” province. A detailed discussion of the Normative Characters follows, where Washington notes that normative quartz is rare, and most of the rocks are nepheline or leucite normative. He also notes that in the Campanian District, the three magmatic centers have distinct rock chemistry with those of the Island of Ischia more closely related to Campi Flegrei than to Vesuvius. A very instructive section follows, where Washington compares the Roman comagmatic region with others such as the Bohemian, Eifel, Laacher See, and especially the Highwood District in Central Montana, extensively studied by his colleague, L.V. Pirsson. The two concluding sections are on the formation of leucite and the distribution of barium. Leucite phenocrysts are a nearly universal mineralogical characteristic of the Roman comagmatic region rocks, and where it appears in the norm, it also is in the

15

16

Chapter 2 The contributions and influence of two Americans

mode, in contrast to nepheline. Washington gives a set of conditions seemingly required for leucite formation; low silica content ( 1. Washington compares the distribution of barium in the Roman comagmatic region with other areas and notes that its concentration increases with increasing K2O, and analyses suggest that it is in potassium feldspars, not leucite. He also notes that ZrO2 has a predilection for sodic rocks and Cr2O3 for magnesia-rich rocks.

Publications from 1906 to 1912 In the summer and autumn of 1905, Washington visited the volcanic districts of Catalonia, Sardinia, Pantelleria, and Linosa, with the aid of a grant from the Carnegie Institution of Washington (incorporated by United States Congress in 1902; now also called the Carnegie Institution for Science). During this period, his work as a consulting mining geologist limited his basic research. Washington published studies on two islands near Sicily, Pantelleria and Linosa (Washington, 1908, 1909; Washington and Wright, 1908, 1910). The publications with F.E. Wright marked the start of his collaboration with members of the Geophysical Laboratory of the Carnegie Institute of Washington, recently founded on December 12, 1905. Other studies related to the southern Mediterranean regions concerned Catalan volcanoes (Washington, 1907a) and the titaniferous basalts of the western Mediterranean (Washington, 1907b). He also continued his research on leucite [K(AlSi2)O6] that he started in The Roman Comagmatic Region 1906 with two papers (Washington, 1907c,d). He maintained his collaboration with Cross, Iddings, and Pirsson, and they published articles on igneous rock textures (Cross et al., 1906) and modifications to their quantitative rock classification (Cross et al., 1912).

Publications after joining the Geophysical Laboratory, Carnegie Institution of Washington Publications 1912 to 1919 The Geophysical Laboratory was established in 1905 as part of the Carnegie Institution of Washington to investigate the processes that control the composition and structure of the Earth, including development of the underlying physics and chemistry and to create the experimental tools required for the many experimental

Chapter 2 The contributions and influence of two Americans

tasks. Arthur L. Day was the first director of the Geophysical Laboratory in 1906 and had come from the Division of Physical and Chemical Research of the USGS. Henry S. Washington was hired as a petrologist (Fig. 2.2) in 1912 and remained there until his death in 1934, except for a period during World War I when
at the American Embassy in Rome. he was scientific attache Presumably, he moved his analytical laboratory from Locust, New Jersey to the new Geophysical Laboratory campus on Upton Street, Washington, D.C. (Fig. 2.3).

Figure 2.2 H.S. Washingtons business card that notes his new address.

Figure 2.3 Henry S. Washington, c.1922, in the Geophysical Laboratory, preparing to analyze Hawaiian rocks. Photo from Picryl Public Domain.

17

18

Chapter 2 The contributions and influence of two Americans

During his graduate studies at Yale, Washington had collaborated with the USGS Chief Chemist, W.F. Hillebrand. After moving to the Geophysical Laboratory, he could now further develop relationships with the USGS. Mary G. Keyes, who had worked in the USGS thin section laboratory with Frank S. Reed and John L. Mergner, was hired as Washington’s assistant and became a coauthor on some publications. In the summer of 1914, Washington accompanied Geophysical Laboratory Director Arthur L. Day on a tour of the volcanoes of southern Italy, which included Vesuvius, Etna, and the Aeolian Islands of Vulcano, Lipari, and Stromboli; only Stromboli was active. In Washington and Day (1915), a detailed description of the 1914 repose state of Vesuvius is given. Other publications before and after his 1914 excursion are related to other Italian volcanoes and dealt with studies of Sardinia (Washington, 1913a,b; 1914a, 1915; Washington and Merwin, 1915), Stromboli (Washington, 1917a; Kozu and Washington, 1918), Pantelleria (Washington, 1913c, 1914b), and leucite in Italian lavas (Washington, 1918). In 1917, Washington published a monumental tome of 1201 pages containing 8602 tabulated analyses and many comments on analytical quality (Washington, 1917b). The 1917 publication was a greatly enlarged version of USGS Professional Paper 14 published in 1903, which contained only 2881 analyses. This publication contains all of Washington’s rock chemistry of samples collected from Campi Flegrei, Vesuvius, and the Island of Ischia as well as other Italian samples. As part of a book review (Feininger, 2002) of Igneous Rocks: A Classification and Glossary of Terms Second edition, Tomas Feininger comments on an omission concerning the CIPW classification: That vast and ambitious classification scheme, based on, yes, quantitative geochemical analyses, flourished not yesterday, but a century ago. It produced hundreds (if not thousands) of new rock names, most now mercifully forgotten, and led to a magnificent compilation of 8602 geochemical analyses in a huge (1201 pages, 4 kg) and timeless publication: Chemical Analyses of Igneous Rocks by Henry S. Washington (U.S. Geol. Surv., Prof. Pap. 99, 1917).

Publications 1920e1934 No publications, except one, Washington and Merwin (1921), directly related to the Naples volcanoes were published during the later part of Washington’s research career, but there were

Chapter 2 The contributions and influence of two Americans

many concerned with other Italian volcanic regions and related rocks: Etna (Washington et al., 1926), Lipari (Washington, 1920a), Vulcano (Washington, 1924), Alban Hills (Washington and Merwin, 1923), and Roccamonfina (Washington, 1920b, 1927). During this period, Washington undertook, some with Mary G. Keyes, a detailed study of the major Hawaiian Island volcanoes (e.g., Washington, 1923a,b,c,d; Washington and Keyes, 1926, 1928). He also collaborated with Frank W. Clarke (USGS) and published a major work on the composition of the earth’s crust (Clarke and Washington, 1924) and completed the fourth Edition of his Manual of the Chemical Analysis of Rocks (Washington, 1930).

Significance to Italian geology and petrology Perhaps the most enduring contribution to the knowledge of Italian volcanism is his 1906 publication The Roman Comagmatic Region. Here, he documented the extreme potassium enrichment of the volcanic rocks, described in great detail their constituent mineralogy and rock chemistry, and suggested that the volcanoes comprising this petrographical province were genetically related. To petrology in general, his most lasting contribution is the collaboration with Cross, Iddings, and Pirsson developing the CIPW norm. The Italian scientific establishment appropriately recognized Washington’s contributions to Italian geology. He was Cavalier, Order of the Crown, Italy, and a foreign member of Accademia Nazionale dei Lincei (Roma), Societa Geologica Italiana, R. Accademia di Scienze, Lettere ed Arti degli Zelanti (Acireale, Sicilia), R., and Accademia delle Scienze (Torino, Modena).

Stories and anecdotes After a long illness, Henry S. Washington died at his home in Washington, D.C. on January 7, 1934, a few days short of his 67th birthday. Many obituaries, remembrances, and stories use many accolades “ . one of the most eminent and picturesque personalities in American science . ” (Fenner, 1934), and “Dr. Henry Stephens Washington was one of the most remarkable men I ever met, a polished gentleman, a well-read scholar, full of curiosity, a tireless researcher, and an unabashable linguist” (Gibson, 1983). One story told by Ralph E. Gibson (1983) deserves mentioning.

19

20

Chapter 2 The contributions and influence of two Americans

When I knew him, he lived in rooms over a restaurant on M Street (it may have been N) near Logan Circle [located in northwest Washington, D.C.] kept by an Italian named Tarino and his wife. According to Dr. Washington, they served the best Italian food in Washington and, judging from the few times I dined with him there, I can well believe him. Prohibition was not well received by Harry Washington [known to his friends as Harry (cf. Milton,1991)], who genuinely regarded it as an insult to civilization in depriving mankind, or at least the American genus homo of the highest products of art - vintage wine. However, he dared and drank.

Frank Alvord Perret In December 1903, Frank Alvord Perret arrived in Naples, Italy. Perret was a native of Brooklyn, New York, an inventor, electrical engineer, and successful industrialist who manufactured products of his own design. But the year before, at age 35, Perret had suffered a nervous breakdown. He had come to Naples to recuperate, and Vesuvius, then in eruption, gave him the opportunity to start his life anew. Perret had come to one of the most accessible, active, and complex volcanic landscapes in the world, and Italian volcanologists welcomed him with open arms. Subsisting on a trickle of royalties from his inventions (Douglas, 1937), private support from a group of United States businessmen, and, from 1917, on a small stipend from the Carnegie Institution of Washington (Yoder, 1998), he lived in Naples almost continuously for the next 20 years. He monitored Vesuvius through the explosive 1906 eruption, the 1906e1913 repose period, and from 1913 to 1921 after eruptive activity resumed. During his years in Italy, Perret teamed with Italian volcanologists, introduced new technologies, collected data, and worked with the government to calm and instruct the public during volcanic crises. He observed eruptions at Stromboli (years 1907, 1909, 1912, 1915) and Etna (years 1908, 1910, 1923) and studied the Campi Flegrei. Perret flourished in Italy, and his research there brought him international renown. He traveled to eruptions at Tenerife (year 1909) and Sakurajima (year 1914), and he was the first volcanologist on station at the Hawaii Volcano Observatory on Kilauea (1910e11). For his service in the 1906 eruption, Perret was knighted by Italy’s King Victor Emmanuel III. In the 1890s, Perret had stood at the forefront of the Electric Age. He had dropped out of the Brooklyn Polytechnic Institute

Chapter 2 The contributions and influence of two Americans

to work as an assistant to Thomas Edison (Douglas, 1937), and, by 1902, companies in Brooklyn and Springfield, Massachusetts, had produced his electric cars, street car motors, arc lamps, dynamos, elevators, and lightweight batteries (Gidwitz, 2005). But the pressures of business took their toll. That spring, he collapsed, and he took refuge in his parents’ Brooklyn home to heal. On
e, Martinique, erupted May 8, while he was convalescing, Mt. Pele and killed 29,000 people. The eruption baffled scientists (Jaggar, 1956), but the challenge of its mystery and inconceivable loss of life invigorated Perret. It convinced him, along with medical advice that he find a new occupation and place to live, that volcanology was the career “for which he was destined,” he later wrote. “For this task a certain grounding in physics and special work in electrical engineering, with some chemistry and astronomy, seemed a not inadequate preparation” (Perret, 1937: p. 17). Perret must also have seen newspaper stories in 1903 that reported Vesuvius was erupting and that lava flows and explosions and panic had engulfed Naples (Anon, 1903a,b,c,d). By New Year’s Day, 1904, Perret was ensconced in Torre del Greco, in an apartment with a view of Vesuvius’s summit. On January 4, he stood for the first time on the crater rim, taking pictures as lava fountained and explosions launched ash high above his head (Perret, 1924). Perret had never seen a volcano before, but he had an exacting eye and an uncanny ability to discern and describe the components of unfolding physical processes. In his first encounter with erupting lava in early 1904, he braved the risk of explosions and landslides in the Valle dell’Inferno on Vesuvius’ eastern side to record the lava’s rate of flow, the height of the small cone from which it poured, the contrast with the older lava beneath it, and to deduce how its rapid outflow had caused the main crater to collapse months before (Perret, 1924). Perret roamed the volcano and soon made friends with the director of the Royal Vesuvius Observatory, Raffaele Vittorio Matteucci. The Observatory had been built in the 1840s with funds from King Ferdinand II (Civetta et al., 2004), but government support had been scarce ever since. When Matteucci took over in 1903, the building had stood empty for years (Civetta et al., 2004), and he recognized Perret as a kindred soul and an asset for his resource-starved institution. In September 1905, he appointed Perret his unpaid “Honorary Assistant” (Perret, 1924). Through 1904 to 1905, lava stood high in Vesuvius’s conduit. Perret and Matteucci watched it pond in the crater and then build a small scoria cone, which grew to fill the crater, and rise

21

22

Chapter 2 The contributions and influence of two Americans

above its rim. In May 1905, Vesuvius stood 1335 m tall, and lava still spilled over the lip of the cone, sailed hundreds of meters into the air, and burst from vents lower down the mountain (Perret, 1924). On April 4, 1906, “the usual white vapor was seen issuing from the crater with a subtly but decidedly unusual aspect impossible to describe,” he wrote. “As the skilled physician sees in the patient a significant change which to other eyes is not revealed, so the volcanologist, observing the crater on this day, saw there the signature of a new power” (Perret, 1924: p. 33). That afternoon, Vesuvius began to fracture, and by April 7, lava was spilling from vents on its southeast side. The plume grew higher, wider, and darker. The volcano launched two-ton blocks as far as the base of the main cone and rained ash on Naples. As it thundered with staccato explosions two or three times per second, Perret saw something never reported before. In the instant before the sound reached him, “a thin luminous arc would flash upward and outward from the crater and disappear into space” (Perret, 1924: p. 40). These flashing arcs were the explosions’ shock waves, speeding outward in all directions, reflecting and refracting sunlight in an inflating, glistening ball. Perret and Matteucci followed the lava streams, warning the last tourists on the slopes to return to the city. The eruption continued to intensify. As a “pillar of liquid fire” shot kilometers above the crater, they returned to the Observatory, although they feared, at any moment, to be buried in lava or ash (Anon, 1906). After midnight on April 8, after hours of constant and ever-stronger seismic shocks, the men fled the building as its walls began to crack. At 3:30 a.m., they watched the mountain’s upper cone peel outward “like the falling of the petals of a flower” (Perret, 1924: p. 40). The last lava had been ejected from the conduit, and a jet of gas roared skyward. At sunrise, it was soaring 13 km into the sky, forming pure white steam “‘cauliflower heads’ with a sharpness of contour and a wealth of detail impossible to describe” (Perret, 1924: p. 45). Perret and Matteucci were the only volcanologists with a clear view of the summit’s destruction, a spectacle essential to Perret’s recognition that this “paroxysmal emission of gas” formed a separate phase of the eruption and “that gas is the principal eruptive element and that all else is accessory.failure to realize this basic truth has been the cause of many errors in the conception of volcanic phenomena” (Perret, 1924: p. 80). On April 9, the gas ejection waned, and the plume grew dense and dark. For more than a week, ash fell over the region in a blanket as much as 90 cm deep (Matteucci et al., 1906).

Chapter 2 The contributions and influence of two Americans

Figure 2.4 Heroes of Duty, an Italian postcard, April 1906. Left to right: Brigadier of the Carabinieri Migliardi; Professor Raffaele Vittorio Matteucci, Director of the Royal Vesuvius Volcano Observatory; Frank Alvord Perret; and railroad station chief Mormile (Gidwitz, 2005).

One hundred thousand people fled Naples; in San Giuseppe, 105 people died when a church roof collapsed (Perret, 1924). Perret, Matteucci, a railroad station telegrapher, and six members of the national police remained in the Observatory. Their daily dispatches, relayed by telegram and courier, were printed and posted throughout the region, inspiring frightened residents that “if men could live upon the mountain itself, life was surely possible elsewhere” (Perret, 1924: p. 49; Fig. 2.4). On April 18, an easterly gale pushed the plume down toward the Observatory. The air was opaque with ash, but Perret, Matteucci, and the Carabinieri managed to lead 50 people, who had sought shelter in a nearby building, through the gloom and into the Observatory for safety. For hours, they struggled to breathe in the dust and carbon dioxide that seeped into the building; at midnight, when the plume lifted, a young man in the group lay dead (Perret, 1907a). By April 22, the eruption was over. Vesuvius had killed 216 people, left 34,000 homeless (Chester et al., 2015), disgorged some 13 million cubic meters of lava (Perret, 1950), and blew off the top 115 m of its cone (Perret, 1924). The world’s leading volcanologists had flocked to Naples to observe the eruption. In the sunny days after it waned,

23

24

Chapter 2 The contributions and influence of two Americans

Figure 2.5 Frank A. Perret, age 48. In his lapel is the Knight of the Italian Crown rosette, awarded for his brave work during the 1906 Vesuvius eruption. From Frank A. Perret, Volcanologist The Worlds Work, v. 29, #6, April 1915; public domain.

Alfred Lacroix, Henry Johnston-Lavis, Thomas Jaggar, Albert Brun, Tempest Anderson, and Lajos Lóczy, along with the King and Queen of England, the ex-Empress of France, and many other notables, climbed up through the ash to honor the Observatory team (Perret, 1924). The men in the Observatory were cheered as heroes, and King Victor Emmanuel III awarded Matteucci and Perret (Fig. 2.5) each the Cross of Cavaliere Ufficiale of the Order of the Crown of Italy (Anon, 1907a). But in May 1907, when Perret was to receive his medal from Queen Dowager Margherita in Rome, he was instead on Stromboli (Anon, 1907b), where summit explosions and heavy showers of scoriae had shattered windows, destroyed the island’s crops, and panicked residents. Perret believed that active volcanoes responded to tidal forces; after studying the sun and moon’s trajectory and two trips to the crater, he correctly predicted the eruption would slacken and convinced authorities to cancel a planned evacuation (Perret, 1907b). Vesuvius lay quiet for the next 7 years, in what Perret called a “repose period” (Perret, 1924: p. 97). He saw this as an opportunity to monitor the volcano with traditional instruments, new technologies, and devices of his own invention. Perret believed that only photographs could serve as accurate, permanent records of volcanic eruptions (Perret, 1914), and he

Chapter 2 The contributions and influence of two Americans

had arrived in Italy with a state-of-the-art camera, the Kodak 3A. Introduced in 1903 (Bilotta, 2002), the pocket-sized 3A used massproduced roll film instead of fragile and easily scratched glass plates. There is much, however, that a camera cannot capture. To describe an eruption’s character and its many, fleeting facets, Perret devised a circular diagram on which an observer can quickly plot the changing details of volcanic activity, such as the condition of the cone, the character of lava flows, and the intensity and nature of earthquakes, ejecta, and electrical phenomena (Perret, 1914). Perret was convinced that audible sound could lend insights into a volcano’s state. Ten days before the 1906 eruption, as he spent the night at the Eremo Hotel next to the Observatory, he heard a faint, continuous sound rising from beneath the floor. Borrowing a technique that the deaf Thomas Edison used to test early phonographs, he pressed his upper teeth against his iron bedstead, and the vibrations buzzed in his skull. The experience inspired him to build portable microphones to monitor and record subterranean volcanic sounds (Perret, 1950). He developed a field microphone that weighed less than a pound (Fig. 2.6). Secured in a metal case, placed directly on the ground or at the mouth of an upturned gramophone horn, it allowed its operator to listen through headphones and record its signal on custom-made gramophone cylinders coated with soft wax (Perret, 1918). Another unit, powered by a flashlight battery, used an amplifier made of watch parts, silk thread, and a thin celluloid pointer to trace the sound waves on smoked paper (Perret, 1924). Perret monitored seismic shocks with shimmering saucers of mercury (Perret, 1924) and with devices made of twisted rope, lava rock, levers, and a ball of iron (Perret, 1924). He collected fumarolic gases with vacuum tubes and aspirating pumps, and, to preserve volcanic gases for laboratory study, he sealed glowing blobs of lava in metal cans and coated fresh bombs in rubber and wax (Perret, 1924). He dangled cans of snow over steaming lava to collect condensed vapor (Perret, 1950), and he was the first volcanologist in Italy to use a thermoelectric pyrometer (Perret, 1924). His chemical test kit was designed for the challenging volcanic environment, where winds can be strong and visibility poor: a glass rod, coated with acidified silver nitrate, to detect hydrogen chloride; lead acetate for hydrogen sulfide; limewater for carbon dioxide; and filter papers, coated with zinc chloride, potassium ferrocyanide, and ammonia, to register sulfur dioxide (Perret, 1924).

25

26

Chapter 2 The contributions and influence of two Americans

Figure 2.6 Perret built his own microphones and amplifiers in hopes of detecting magmas subterranean movements. Here, he listens at the Campi Flegrei, in Pozzuoli, Italy. From The Days Work of a Volcanologist, The Worlds Work, V. 25, November 1907; public domain.

In 1909, Matteucci died of bronchopneumonia, his lungs ravaged by ash, and the damp drafts in the still-derelict Observatory (Gasparini, 2009). Giuseppe Mercalli became director in 1911, but in 1914, after Vesuvius began to reawaken, he died in a fire in his Observatory apartment. His assistant, Alessandro Malladra, was appointed acting director and ultimately permanent director in 1927 (Langella, 2018). Perret and Malladra were close in age, and they were frequent collaborators. Malladra even adopted Perret’s method for monitoring the mountain’s subterranean throbbing, which, he wrote, “could be better heard by resting one’s head on the floor or on the headboard of the bed” (Malladra, 1918: p. 157). In 1914, the crater vent was ejecting lava, and a small cone began to rise. By August 1916, the cone was 60 m high; it spat and sprayed lava and resounded with a metallic clang (Perret, 1924). Malladra and Perret made a series of 24-hour visits to the crater in August of 1916, 1917, and 1919, on dates when

Chapter 2 The contributions and influence of two Americans

Perret calculated that the moon and sun would render the volcano relatively quiet (Perret, 1924). In 1916, they measured fumarolic and lava temperatures, gathered rock and mineral samples, and collected 300 mL of condensed vapor, amassed over 12 h, from a fumarole that directly vented the volcanic chimney (Perret, 1924). Conditions were harshdhydrogen fluoride gas etched Perret’s camera lens (Perret, 1924)dand newspapers as far away as New Zealand reported their feat (Anon, 1916). During World War I, it was almost impossible to travel with instruments and a camera (Perret, 1918), but Perret volunteered with the American Red Cross (Fig. 2.7) and in “the uniform of an American Officer, I could go anywhere.” He held a captain’s rank, and “it alone made possible the continuing of the work” (Perret, 1923b). Perret had always been deeply sympathetic to poor and orphaned children, and he was in charge of the Red Cross’s child welfare programs and milk distribution in Naples (Bakewell, 1920). He also worked with military authorities to test his microphones’ ability to detect countermines and tunneling (Perret, 1950). In 1917, Perret examined the Solfatara di Pozzuoli, on behalf of investors in a proposed geothermal electric plant. He sank borings up to 6 m deep; 1 m below the surface, he found a layer of hot, wet clay that extended over the entire crater, the remnant, he said, of a lake of boiling mud (Perret, 1918). His ground-contact microphone revealed three subterranean fractures extending from the Bocca Grande (Perret, 1924).

Figure 2.7 Perret in his US Army uniform, when he was serving in the Red Cross in Italy. Courtesy of the Geophysical Laboratory, Carnegie Institution for Science; public domain.

27

28

Chapter 2 The contributions and influence of two Americans

Perret observed more eruptions at Stromboli in 1909, 1912, and 1915 and at Mt. Etna in 1910 and 1923. During the latter visit, he felt the effects of his years in harsh environments. “I am glad to say that I got through the physical investigation better than I feared, though heart and lungs were not exactly in shape for ten hours of mule riding and hard climbing, and heat and gas exposure which were really extreme” (Perret, 1923a). By July 1923, depressed and crippled by illness, he was selling his belongings to pay for his return to New York (Perret, 1923a). Most of his colleagues, he lamented, lacked the vision to see what was important to the field. “How I mourn the loss of the old giantsdthe Mercalli’s, Matteucci’s and Johnston-Lavis’s. You can have no idea how bad things are in that respect” (Perret, 1923b). In 1924, the Carnegie Institution published Perret’s The Vesuvius Eruption of 1906: Study of a Volcanic Cycle. It describes the eruptive periods from 1903 to 18 and offers the most comprehensive description of the 1906 eruption. (Matteucci waited in vain for the government to fund a full report; he published a fraction of his data as a series of bullet points (Matteucci et al., 1906). Mercalli died before completing his final account.) Italian volcanoes are also prominent in Perret’s Volcanological Observations (Perret, 1950). Perret’s health was precarious for the rest of his life, although
e Volcahe was strong enough to create and to man the Mt. Pele nological Observatory, Martinique, during the volcanic crisis of 1929e32. “All I can think of doing for the lease of life which may remain to me, is to do my best to contribute as much as possible to volcanological science” (Perret, 1931). He was at his post virtually around the clock, in all weather, often in clouds of caustic gas and abrading ash. In 1941, sickened and weak, he returned to New York City. He died on January 12, 1943.

Acknowledgments We thank John E. Repetski and John R. Keith (both US Geological Survey Emeritus) for their helpful reviews. We also thank Shaun Hardy (DTM/Geophysical Laboratory Library of the Carnegie Institution for Science) for his expert help with the Perret documentation.

References Anon, January 1, 1903a. Vesuvius in eruption. N. Y. Times 29. Anon, August 7, 1903b. State of Panic in Naples. N. Y. Times 15. Anon, August 7, 1903c. Weird scene on Vesuvius. N. Y. Times 29. Anon, August 6, 1903d. Eruption of Vesuvius continues. N. Y. Times 31. Anon, July 6, 1906. American scientist, back from Vesuvius. N. Y. Times 31.

Chapter 2 The contributions and influence of two Americans

Anon, 1907a. Professor F. A. Perret Is Decorated by King (The Brooklyn Daily Eagle 4 January. 5). Anon, May 2, 1907b. Americans’ Doings in the Eternal City, vol. 19. The New York Times. Anon, 1916. Vesuvius filling up (Omaru Mail, 2 December. 9). https://paperspast. natlib.govt.nz/newspapers/oamaru-mail/1916/12/02/9. Bakewell, C.M., 1920. Story of the American Red Cross in Italy. Macmillan, New York. Barth, T.F.W., 1936. Henry Stephens Washington. Mineralogische und Petrographische Mietteilungen 47, 371e372. Bilotta, S., 2002. Scott’s photographica collection, Eastman Kodak company 3A folding pocket Kodak camera. http://www.vintagephoto.tv/3afpk.shtml. Chester, D., Duncan, A., Kilburn, C., Sangster, H., Solana, C., 2015. Human responses to the 1906 eruption of Vesuvius, southern Italy. J. Volcanol. Geotherm. Res. 296, 1e18. Civetta, L., Cuna, L., De Lucia, M., Orsi, G., 2004. Il Vesuvio negli occhi: Storie di osservatori. Unità Funzionale di Vulcanologia e Petrologia, Istituto Nazionale di Geofisica e Vulcanologia -Sezione di Napoli j Osservatorio Vesuviano. http://www.ov.ingv.it/ov/doc/vesuvio_negli_occhi.pdf. Clarke, F.W., Washington, H.S., 1924. The Composition of the Earth’s Crust. U.S. Geological Survey Professional Paper 127, Washington. Cross, W., Iddings, J.P., Pirsson, L.V., Washington, H.S., 1902. A quantitative chemico-mineralogical classification and nomenclature of igneous rocks. J. Geol. 10 (6), 555e690. Cross, W., Iddings, J.P., Pirsson, L.V., Washington, H.S., 1906. The texture of igneous rocks. J. Geol. 14 (8), 692e707. Cross, W., Iddings, J.P., Pirsson, L.V., Washington, H.S., 1912. Modifications of the “quantitative system of classification of igneous rocks”. J. Geol. 20 (6), 550e561. Douglas, M.S., 1937. He talks with volcanoes. Saturday Evening Post. 210 (26), 6e7 (32-33). Feininger, T., 2002. Book review of igneous rocks: a classification and glossary of Terms (recommendations of the IUGS subcommission on the systematics of igneous rocks). In: LeMaitre, R.W. (Ed.), vol. 40. Cambridge University Press, New York, NY, pp. 1737e1738 (The Canadian Mineralogist). Fenner, C.N., 1934. Obituary Henry Stephens Washington. Science 79 (2038), 47e48. Gasparini, P., 2009. Giuseppe Mercalli. http://www.paologasparini.unina.it/wpcontent/uploads/2016/10/Giuseppe_Mercalli.pdf. Gibson, R.E., 1983. Henry Stephens Washington in places and persons [excerpts from an as yet unpublished autobiography by R.E. Gibson]. Johns Hopkins APL Tech. Dig. 4 (4), 237. Gidwitz, T., 2005. The Hero of Vesuvius. http://www.vesuvius.tomgidwitz.com/ html/2_the_engineer.html. Hillebrand, W.F., Washington, H.S., 1888. Notes on certain rare copper minerals from Utah. American Journal of Science 35 (208), 298e307 (third series). Jaggar, T.A., 1956. My Experiments with Volcanoes. Hawaiian Volcano Research Association, Honolulu. €r Keyes, M.G., 1934. Henry Stephens Washington, vol. 16. Zeitschrift fu Vulkanologie, Bd, pp. 1e6. H. 1. Kozu, S., Washington, H.S., 1918. Augite from Stromboli. American Journal of Science 45 (270), 463e469 (fourth series).

29

30

Chapter 2 The contributions and influence of two Americans

Langella, A., 2018. L’Osservatorio Vesuviano da Macedonio Melloni ad Alessandro Malladra. http://www.vesuvioweb.com/it/wp-content/uploads/ Aniello-Langella-LOsservatorio-Vesuviano-da-Macedonio-Melloni-adAlessandro-Malladra-vesuvioweb-2018c.pdf. Lewes, J.V., 1935. Memorial of Henry Stephens Washington. Am. Mineral. 20, 179e184. Malladra, A., 1918. Riassunto sull’ attività del Vesuvio per l’anno 1917. Bollettino della Soc. dei Nat. Napoli 31 (2), 132e163. Matteucci, R.V., Nasini, R., Casoria, E., Fiechter, A., 1906. Appunti sull’eruzione Vesuviana 1905e1906. Boll. Soc. Geol. Ital. 25, 846e856. Merwin, H.E., 1952. Memorial to Henry Stephens Washington. Proceedings Volume of the Geological Society of America Annual Report of 1951, pp. 165e172. Milton, C., 1991. Henry Stephens Washington, vol. 60. National Academy of Sciences Biographical Memoirs, pp. 367e392. Perret, F.A., 1907a. The day’s work of a volcanologist. The World’s Work 15 (1), 9544e9554. Perret, F.A., 1907b. Notes on the eruption of Stromboli, April, May, June, 1907. Brooklyn Inst. Mus. Sci. Bull 1 (11), 313e323. Perret, F.A., 1914. The diagrammatic representation of volcanic phenomena. Am. J. Sci. 37 (217), 48e56. Perret, F.A., 1918. Report on Volcano Studies at Naples, vol. 16. Carnegie Institution of Washington Year Book 1917, pp. 137e140. Perret, F.A., 1923a. Letter to Arthur L. Day, 9 July. Perret, F.A., 1923b. Letter to Arthur L. Day, 24 July. Perret, F.A., 1924. The Vesuvius Eruption of 1906: Study of a Volcanic Cycle. No. 339. The Carnegie Institution of Washington, Washington. Perret, F.A., 1931. Letter to Arthur L. Day, 8 October.
e, 1929-1932. No. 458, Second Perret, F.A., 1937. The Eruption of Mt. Pele Printing. Carnegie Institute of Washington, Washington. Perret, F.A., 1950. Volcanological Observations, vol. 549. The Carnegie Institution of Washington, Washington. Spencer, L.J., 1936. Henry Stephens Washington. Biographical notices of mineralogists recently deceased. (Sixth series). Mineral. Mag. 24 (153), 304e305. Waldstein, C., Washington, H.S., 1891. Excavations by the American School at plataia in 1891. Discovery of a temple of Archaic plan. Am. J. Archaeol. Hist. Fino Arts 7 (4), 390e405. Washington, H.S., 1894a. On the basalts of Kula. Am. J. Sci. 47 (278), 114e123 (third series). Washington, H.S., 1894b. On the possibility of assigning a date to the Santorini vases. Am. J. Archaeol. Hist. Fino Arts 9 (4), 504e520. Washington, H.S., 1896a. On some Ischian trachytes. Am. J. Sci. 1 (5), 375e385 (fourth series). Washington, H.S., 1896b. Italian petrological Sketches. J. Geol. 4 (5), 541e566. Washington, H.S., 1896c. Italian petrological Sketches. II. The Viterbo region. J. Geol. 4 (7), 826e849. Washington, H.S., 1897a. Italian petrological Sketches. III. The Bracciano, Cerveteri and Tolfa regions. J. Geol. 5 (1), 34e49. Washington, H.S., 1897b. Italian petrological studies. IV. The Rocca Monfina region. J. Geol. 5 (3), 241e256. Washington, H.S., 1897c. Italian petrological Sketches. V. Summary and conclusion. J. Geol. 5 (4), 349e377.

Chapter 2 The contributions and influence of two Americans

Washington, H.S., 1898. The identification of the marbles used in Greek sculpture. Am. J. Archaeol. 2 (1e2), 1e18 (second series). Washington, H.S., 1899. Some analyses of Italian volcanic rocks I. Am. J. Sci. 8 (46), 286e294 (fourth series). Washington, H.S., 1900. Some analyses of Italian volcanic rocks II. Am. J. Sci. 9 (49), 44e54 (fourth series). Washington, H.S., 1906. The Roman Comagmatic Region. Carnegie Institution of Washington, Washington, p. 57. Washington, H.S., 1907a. The Catalan volcanoes and their rocks. Am. J. Sci 24 (141), 217e242 (fourth series). Washington, H.S., 1907b. The titaniferous basalts of the western Mediterranean: a preliminary notice. Q. J. Geol. Soc. 63 (1e4), 69e79. Washington, H.S., 1907c. The formation of leucite in igneous rocks. J. Geol. 15 (3), 257e279. Washington, H.S., 1907d. The formation of leucite in igneous rocks (continued). J. Geol. 15 (4), 357e395. Washington, H.S., 1908. Linosa and its rocks. J. Geol. 16 (1), 1e35. Washington, H.S., 1909. The submarine eruptions of 1831 and 1891 near Pantelleria. Am. J. Sci. 27 (158), 131e150 (fourth series). Washington, H.S., 1913a. Some lavas of Monte arci, Sardinia. Am. J. Sci. 36 (216), 577e590 (fourth series). Washington, H.S., 1913b. The volcanic cycles in Sardinia. Comptes Rendus du
ologique international, 12th IGC [Toronto], pp. 229e239. 12e Congrès ge Washington, H.S., 1913c. The volcanoes and rocks of Pantelleria Part II. J. Geol. 21 (8), 683e713. Washington, H.S., 1914a. The analcite basalts of Sardinia. J. Geol. 22 (8), 742e753. Washington, H.S., 1914b. The volcanoes and rocks of Pantelleria Part III. J. Geol. 22 (1), 16e27. Washington, H.S., 1915. Contributions to Sardinian petrography; I, the rocks of Monte ferru. Am. J. Sci. 39 (233), 513e529 (fourth series). Washington, H.S., 1917a. Persistence of vents at Stromboli and its bearing on volcanic mechanism. Bull. Geol. Soc. Am. 28 (1), 249e278. Washington, H.S., 1917b. Chemical Analyses of Igneous Rocks Published from 1884 to 1913, Inclusive, with a Critical Discussion of the Character and Use of Analyses. U.S. Geological Survey Professional Paper, Washington, D.C, p. 99. Washington, H.S., 1918. Italian leucite lavas as a source of potash. Metall. Chem. Eng. 18, 65e71. Washington, H.S., 1920a. The rhyolites of Lipari. Am. J. Sci. 50 (300), 446e462 (fourth series). Washington, H.S., 1920b. Italite: a new leucite rock. J. Wash. Acad. Sci. 10 (9), 270e272. Washington, H.S., 1921. Obsidian from copan and Chichen Itza. J. Wash. Acad. Sci. 11 (20), 481e487. Washington, H.S., 1922. The Jades of Middle America. Proc. Natl. Acad. Sci. U.S.A 8 (11), 319e326. Washington, H.S., 1923a. Petrology of the Hawaiian Islands; I, Kohala and Mauna Kea, Hawaii. Am. J. Sci. 5 (30), 465e502 (fifth series). Washington, H.S., 1923b. Petrology of the Hawaiian Islands; II, Hualalai and Mauna Loa. Am. J. Sci 6 (32), 100e126 (fifth series). Washington, H.S., 1923c. Petrology of the Hawaiian Islands; III, Kilauea and general petrology of Hawaii. Am. J.Sci. 6 (34), 338e367 (fifth series).

31

32

Chapter 2 The contributions and influence of two Americans

Washington, H.S., 1923d. Petrology of the Hawaiian Islands; IV, the formation of aa and pahoehoe. Am. J.Sci. 6 (35), 409e423 (fifth series). Washington, H.S., 1924. Notes on the Solfatara of Sousaki (Greece), a recent eruption at Methana (Greece), and recent Maccalube at Vulcano. J. Geol. 32 (6), 460e462. Washington, H.S., 1927. The italite locality of Villa Senni. Am. J. Sci. 14 (81), 173e198 (fifth series). Washington, H.S., 1930. Manual of the Chemical Analysis of Rocks, fourth ed. John Wiley & Sons, New York, NY. Washington, H.S., Day, A.L., 1915. Present condition of the volcanoes of southern Italy. Bull. Geol. Soc. Am. 26 (1), 375e388. Washington, H.S., Keyes, M.G., 1926. Petrology of the Hawaiian Islands, V; the Leeward Islands. American Journal of Science, 12 (70), 336e352 (fifth series). Washington, H.S., Keyes, M.G., 1928. Petrology of the Hawaiian Islands, VI; Maui. Am. J. Sci. 15 (87), 199e220 (fifth series). Washington, H.S., Merwin, H.E., 1915. Nephelite crystals from Monte Ferru, Sardinia. J. Wash. Acad. Sci. 5, 389e391. Washington, H.S., Merwin, H.E., 1921. Note on augite from Vesuvius and Etna. Am. J. Sci. 1 (1), 20e30 (fifth series). Washington, H.S., Merwin, H.E., 1923. Augite of the alban Hills, Italy. Am. Mineral. 8, 104e110. Washington, H.S., Wright, F.E., 1908. On Kaersutite from Linosa and Greenland. Am. J. Sci. 26 (153), 187e211 (fourth series). Washington, H.S., Wright, F.E., 1910. A feldspar from Linosa and the existence of soda anorthite (carnegieite). Am. J. Sci. 29 (169), 52e70 (fourth series). Washington, H.S., Aurousseau, M., Keyes, M.G., 1926. The lavas of Etna. Am. J. Sci. 12 (71), 371e408 (fifth series). Yoder Jr., H.S., 1998. Italian volcanology: geophysical laboratory contributions, 1905-1965. In: Morello, N. (Ed.), Proceedings of the 20th INHIGEO Symposium, Napoli-Eolie-Catania (Italy), 19e25 September 1995. Brigati, Genoa, Italy, pp. 707e726.

3 Kinematics of the TyrrhenianApennine system and implications for the origin of the Campanian magmatism Pietro Paolo Pierantoni,1 Giulia Penza,1 Chiara Macchiavelli,2 Antonio Schettino,1 Eugenio Turco1 1

University of Camerino, School of Science and TechnologydGeology Division, Camerino, MC, Italy; 2Group of Dynamics of the Lithosphere, Institute of Earth Sciences Jaume Almera, Structure and Dynamics of the Earth, Barcelona, Spain

Introduction Large-scale extensional tectonics coupled with orogenic processes characterize the Miocene to recent peri-Tyrrhenian orogenic belt of Italy and Sicily. In central-southern Italy, while the thrust belt, foredeep system of the Apennines Chain, continued migrating toward the present-day Adriatic-Ionian foreland (Patacca et al., 1990; Patacca and Scandone, 2001), the Tyrrhenian margin of the Apennine Chain experienced widespread extensional tectonics characterized by formation of volcanism and several marine and intermontane troughs and basins in Pleistocene times. The Campania Plain, an E-W elongated basin infilled by up to 3000 m of Pleistocene volcaniclastic and alluvial sediments (Milia and Torrente, 1999), is part of this extensional system, which encompasses an area extending from southern Tuscany to the northern margin of Calabria. The Tyrrhenian Sea, which developed since Middle Tortonian times, is the youngest basin of the western Mediterranean (Sartori et al., 2004), and, since the 1960s, it has been subject to several geological and geophysical explorations and surveys. In spite of the huge amount of available data, the geodynamic

Vesuvius, Campi Flegrei, and Campanian Volcanism. https://doi.org/10.1016/B978-0-12-816454-9.00003-1 Copyright © 2020 Elsevier Inc. All rights reserved.

33

34

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

evolution of the Tyrrhenian basin and surrounding regions are not yet well understood, and this has been subject to controversial interpretations (Biju-Duval et al., 1977; Dercourt et al., 1986; Malinverno and Ryan, 1986; Dewey et al., 1989; Boccaletti et al., 1990; Doglioni, 1991; Carmignani et al., 1995; Lavecchia et al., 1995; Faccenna et al., 1996, 2001; Ferranti et al., 1996; Turco and Zuppetta, 1998; Doglioni et al., 1999; Jolivet and Faccenna, 2000; Rosenbaum et al., 2002; Mantovani et al., 2002; Peccerillo and Turco, 2004). In particular, the kinematic relationships between extension in the Tyrrhenian Sea, basin formation in the Tyrrhenian margin of the Apennine Chain, migration of the Apenninic Arcs, and geotectonic setting of volcanism still remain to be determined. The main reasons for the controversial interpretations are due to the complexity of the geodynamic processes that generate the Tyrrhenian-Apennine system. It belongs to the AfricaeEurope collision zone along which, starting from the Upper Oligocene, extrusions of continental blocks and slab-retreat processes occur and have formed back-arc basins and the Apennine Chain. In addition, most of the proposed evolutionary models lack kinematic constraints that can be provided by the main tectonic structures. Instead, models that are well constrained by kinematic data can be incorporated in the global rotation model of the lithospheric plates, are quantitative, and allow to predict geological and geodynamic implications. For the Mediterranean area, tectonic reconstruction models that incorporate these requirements are few: Dewey et al. (1989), Schettino and Turco (2006, 2009; 2011), Argnani (2012), Turco et al. (2012), and Turco et al. (2013). They illustrate the tectonic evolution of the upper plate, through the reconstruction of structural maps. Such maps do not display the evolution of the subducting lithosphere, although the tectonic reconstruction allows determination of the polarity of the subduction and its convergence direction. Therefore, the geometry and the evolution of the subducted lower plate, which in the context of slab-retreat guide the upper plate evolution and the origin of magma, have to be integrated with the help of other methods. Usually, actual slab geometries are investigated through seismic methods (earthquakes foci and seismic tomography). Unfortunately, in the Tyrrhenian area, the available data have insufficient resolution to reconstruct a reliable slab geometry that would allow the correlation with the complex structuring of the upper plate (Faccenna et al., 2014; Brandmayr et al., 2010). To overcome the limits of seismic data, we investigate the slab geometry starting from the kinematic parameters of the

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

structures in the upper plate to determine the evolution of the slab that generated them. For this purpose, we used quantitative tectonic reconstructions of the upper plate and of the lower plate continental margins. For the reconstruction of the Tyrrhenian area, among the few quantitative reconstructions available, we selected two kinematic models that show the best kinematic constraints: Turco et al. (2013) as regard the reconstruction of the upper plate and the one proposed by Schettino and Turco (2011) as regard the reconstruction of the lower plate continental margin.

Geological setting The Apennine Chain The ApennineeMaghreb Chain, represented in the geological sketch map in Fig. 3.1, is considered a Neogene thrust belt that comprises Mesozoic to Palaeogene sedimentary rocks, derived from different basins and shelf paleogeographic domains, located in the Adria continental margin of the African plate (Patacca et al., 1990; Patacca and Scandone, 2007; Scrocca et al., 2003). During the Oligocene, the central-western Mediterranean was characterized by a trench from Alpine Corsica to Kabylies in North Africa, with a slab of Tethys Liguride lithosphere with NW polarity (Turco et al., 2012). The Apennine Chain begins to form as a result of rotation of the Sardinia-Corsica block, along the transform fault that joined trenches of the Alpine and of the Calabrian-Kabylies Arcs. This transform fault, with a sinistral movement, separated trenches, with opposite vergence (Fig. 3.2). The transform maximum length was reached at the end of the rotation of the Sardinia-Corsica block (Fig. 3.3). At the same time, the Ligurian slab, attached to Adria and subduced beneath Calabria, migrated northwestward while sinking into upper mantle. As a consequence, it was juxtaposed to the Corsica block at the end of the rotation phase. The Proto-Apennine Chain is constituted by a me lange of the two accretionary wedges (Western Alpine Arc and Calabrian Arc) and is characterized by complex associations of transcurrent structures along which wedge-top basins were originated. The prominent structuring of the Apennine Chain starts with the extension in the Tyrrhenian area. In the current literature, the Apennine Chain extends from the Sestri-Voltaggio line (Liguria) to the Sangineto Line (North Calabria), which separates it from the Calabrian Arc. This last segment is separated from the Sicilian-Maghrebian Chain by the Taormina line (Fig. 3.1).

35

36

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Figure 3.1 Location map of the main paleogeographic and structural units.

The Apennine Chain can be divided in sectors characterized by homogeneous extensional parameters on the corresponding Tyrrhenian margin (Turco et al., 2013). From North to South, they have identified the following segments (Fig. 3.4): (1) Ligurian-Tuscan-Emilian; (2) Northern Arc; (3) Lazio-Abruzzi Platform; (4) Southern Apennine; (5) Calabrian Arc; and (6) Western-Center Sicilian Chain. The Ligurian-Tuscan-Emilian segment (1) represents the northern side of the Northern Arc and consists of chaotic deposits resulting from oceanic sedimentary recover and boudens of Ligurian ophiolites, covered by thick terrigenous top wedge successions (External Liguride, Macigno,.).

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

37

Figure 3.2 Plate reconstruction of the western Mediterranean region at 33 Ma. The distribution of the continental lithosphere is shown in gray. Present-day coastlines are shown for reference. Areas affected by thinning are shown in light blue. Black arrows represent direction and magnitude of relative motion. Strike-slip faults are shown in yellow. Red lines are convergent boundaries. Blue lines are spreading centers. White lines represent extinct spreading centers. From Turco, E., Macchiavelli, C., Mazzoli, S., Schettino, A., Pierantoni, P.P., 2012. Kinematic evolution of the Alpine Corsica in the framework of Mediterranean mountain belts. Tectonophysics 579, 193e206.

Figure 3.3 Plate reconstruction of the western Mediterranean region at 19 Ma (late Aquitanian). Ap: ProtoApennine Chain. Other symbols are the same from Fig. 3.2. Double arrows represent extensional directions. Dotted areas indicate wedge-top basins. From Turco, E., Macchiavelli, C., Mazzoli, S., Schettino, A., Pierantoni, P.P., 2012. Kinematic evolution of the Alpine Corsica in the framework of Mediterranean mountain belts. Tectonophysics 579, 193e206.

38

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Figure 3.4 Morphotectonic map of the Tyrrhenian-Apennine system, showing normal fault trends (yellow lines) and extension directions in the Tyrrhenian Basin. CA, Calabrian Arc; L-A, Lazio-Abruzzi; SA, Southern Apennine; SCB, Sardinia-Corsica block; T-E, Tuscan-Emilian; U-M, Umbria-Marche; WCS, Western-Center Sicily. Modified from Turco, E., Schettino, A., Macchiavelli, C., Pierantoni, P.P., 2013. A plate kinematics approach to the tectonic analysis of the Tyrrhenian-Apennines System. Rend. Online Soc. Geol. Ital. 29, 187e190.

The Northern Arc (2) is composed of deposits derived from the Adriatic margin, formed by the well-known Umbria-Marche Succession, composed of Middle Jurassic-Miocene basin sediments. The eastern side is identified, in the first phase of its evolution, with the front of the Sibillini Mountains marked by the AnconaAnzio line and in the following phase with the Maiella front identified with the Ortona-Roccamonfina line. Between the two fronts, a thick Mesozoic carbonatic platform succession named Lazio-Abruzzi Platform (3) is incorporated. The segment of the chain, known as Southern Apennine (4), extends from the Ortona-Roccamonfina lineament up to the Sangineto Line (northern Calabria). From the bottom to the top, it is formed by Middle Trias-Lower Cretaceous Lagonegro tectonic units and by Upper Trias-Eocene Panormidi carbonate units.

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

In some areas, the Panormidi carbonate units are overthrusted by oceanic sediments belonging to the Liguride basin, covered by Lower Miocene top wedge sediments (Zuppetta et al., 1984; Zuppetta and Mazzoli, 1995, 1997; Cesarano et al., 2002). On the outer front of the chain, between the sectors 3 and 4, there is a minor arc known as Molisan Arc, which develops from the Maiella front to the Vulture volcano. It is constituted by Jurassic-Cretaceous basin facies successions and small carbonate platforms covered by Mio-Pliocene chaotic and top wedge successions (Patacca and Scandone, 2007). South of the Sangineto Line, the chain continues with the Calabrian Arc (5), up to the Taormina line. It is constituted by an accretionary wedge made of (from bottom to top) Apennine carbonate units, ophiolites (Liguride units), low-grade metamorphic units overthrusted by high-grade metamorphic rocks of continental crust, and locally covered by Triassic-Late Cretaceous sedimentary covers. To the West of the Taormina line extends the SicilianMaghrebian Chain (6) made up of Meso-Cenozoic deposits of basin and carbonate platform, belonging to the African margin. Finally, it is important to underline some special characteristics of the Apennine Chain: (a) the basement is never involved in the construction of the Apennine Chain; (b) although the Apennine Chain is made up exclusively of carbonate rock successions deriving from the Adriatic domain, it is often covered by top wedge sediments whose composition suggests a predominant origin from continental basement rocks; and (c) the whole chain is pervaded by extensional processes during its formation.

The Tyrrhenian Sea The Tyrrhenian Sea is an extensional basin formed between Middle Tortonian times and the Present (e.g., Kastens et al., 1987; Sartori, 1990; Milia and Torrente, 2014). According to Dewey et al. (1989) and Schettino and Turco (2006), the rifting phase of the Tyrrhenian Sea starts at 19 Ma, after the cessation of the seafloor spreading in the Ligurian-Provencal basin. Its formation is due to the rollback and migration of the subducting Ionian plate toward the Southeast (Malinverno and Ryan, 1986; Faccenna et al., 1996). An E-W lineament extending from northern Sardinia to the Campania margin, known as the 41st parallel line and suggested as a lithospheric left-lateral fault by Selli (1981), separates the Tyrrhenian Sea in two sectors. To the North and to the South of the line, values and direction of extension are different, such as crustal and lithospheric thicknesses.

39

40

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

In the northern sector, the continental crust is 20e25 km thick and the lithosphere is around 50e60 km (Panza and Calcagnile, 1979/1980; Nicolich, 1981; Panza, 1984). ODP (Ocean Drilling Program) sites from Kastens et al. (1987) (well 654, Fig. 3.1) find conglomerates covered by Tortonian, Messinian, and PlioPleistocene deposits. The southern sector instead has both a thinned crust (25e10 km or less) and lithosphere (30e50 km) (Panza and Calcagnile, 1979/1980; Nicolich, 1981; Panza, 1984). According to some authors (e.g., Sartori, 1990, 2003; Spadini et al., 1995; Rosenbaum and Lister, 2004), the rifting process in this sector started on the Sardinia margin (10 Ma) and then migrated eastward to the Vavilov basin (5.5 Ma) and to the Marsili basin (2.0e1.8 Ma). Because of the remarkable extension, the presence of oceanic crust is likely to be restricted in these two basins (Sartori et al., 2004; Marani, 2004), as witnessed by the site 651 and 650 (Fig. 3.1). The first shows, from the top, a 388 m-thick PlioceneePleistocene succession (biozone MPL6/ NN18, 2 Ma) above 39 m-thick dolostones, and at the base, the 29 m of highly serpentinized peridotites are covered by a 134 m thick succession of basalts (lava flows and breccias). The second displays, from the top, 32 m of vesicular basalts followed by dolostones and a 602 m-thick succession of Plio-Pleistocene deposits (biozone MPL6/NN18, 2.0 Ma). The multibeam bathymetry from the ISMAR-CNR (Bologna, Italy) for the Tyrrhenian Sea (Marani and Gamberi, 2004) is shown in Fig. 3.4.

Evolution of the upper plate The Tyrrhenian basin formation and the mountain building of the Apennine Chain represent the result of the complex Ligurian-Ionian slab-retreat process produced on the SardiniaCorsica upper plate. To describe the kinematic evolution of the upper plate, we followed the model proposed by Turco et al. (2013), which at the moment seems to be the best constrained by kinematic data. It is inserted in the global rotation model of lithospheric plates, and it is made according to the kinematic constraints provided by the main tectonic structures. The reconstruction is quantitative and allows to predict geological and geodynamic implications. For its realization, the authors have divided the Tyrrhenian-Apennine area into homogeneous sectors, distinguished on the base of their extension kinematic. For each sector, the rotation parameters (Euler poles)

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Table 3.1 Finite reconstruction parameters from Turco et al. (2013). Sector

Time

Latitude

Longitude

Angle

Reference

Tuscany-Emilia Umbria-Marche Lazio-Abruzzo Lazio-Abruzzo Lazio-Abruzzo Lazio-Abruzzo S.Apennine Calabrian Arc Magh-Sicily Magh-Sicily

19 19 3 3 7 7 7 19 2 12

45.45 48.90 0.00 40.44 40.78 42.24 41.23 21.85 0.00 60.81

8.40 10.40 0.00 13.83 13.37 13.83 13.01 6.28 0.00 136.10


20.00
13.00 þ0.00 þ13.57 þ13.88
30.55
45.00 þ12.00 þ0.00 þ0.77

Europe Europe Umbria-Marche Southern Apennine Southern Apennine Africa Europe Europe Europe Calabrian Arc

have been determined on the base of the kinematic of extensional structures (Table 3.1). The software PCME (Schettino, 1998) was used to build the model. According to Turco et al. (2013), the Tyrrhenian extension represents the continuation toward East of the slab-retreat process of Liguride lithosphere, which produced the Balearic basin (Dewey et al., 1989; Turco et al., 2013). From the model, it is possible to highlight four phases of extension of the Tyrrhenian basin. During phase I (19e12 Ma), the accretionary wedge of the Calabrian Arc and the Proto-Apennine Chain separate from the Sardinia-Corsica block (Fig. 3.5). The trench migration to the East increases the length of the entire Apennine Chain, producing extension along it (Fig. 3.6). Phase II starts around 12 Ma ago, during which, due to the transversal extension, the chain is structured in four arcs identifiable with the sectors: Ligurian-Emilian (1), Northern Arc (2 and 3), Calabrian Arc (5), and Western Sicilian (6). The most representative transversal extension areas from North to South are the basin of the Marnoso-Arenacea succession between the sectors 1 and 2; the Molisan basin between the 3 and 5; and the Caltanissetta basin between the sectors 5 and 6 (Figs. 3.6 and 3.7). Phase III starts with the formation of the Vavilov basin (around 7 Ma ago), which marks an important change in the evolution of the Tyrrhenian extension. The Panormide platform,

41

42

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Figure 3.5 Plate reconstruction of the western Mediterranean region at 19 Ma. Lower Miocene Chains are shown in dark gray, the Africa-Adria continental lithosphere is in light gray, Europe is in light brown, the oceanic crust is in blue. Dotted lines are incipient boundaries. Red lines are active boundaries. Black lines are inactive boundaries. Yellow lines are transform faults. Light blue lines are the Jurassic COB (Continent Ocean Boundary) and transfer faults on the continental lithosphere. Dark blue lines are the Middle-Triassic COB and transfer faults on the continental lithosphere. PA, Proto-Apennine; WA, Western Alps. Modified from Turco, E., Schettino, A., Macchiavelli, C., Pierantoni, P.P., 2013. A plate kinematics approach to the tectonic analysis of the Tyrrhenian-Apennines System. Rend. Online Soc. Geol. Ital. 29, 187e190.

which separated the two oceanic areas (Liguride and Ionic) (Fig. 3.3), in this stage of evolution is definitively incorporated into the accretionary wedge (Fig. 3.7). This episode marks the beginning of the differentiation of the Tyrrhenian basin in two areas, roughly separated by the “Selli lineament” of the 41st parallel. To the North, the extension continues with the previous kinematic; to the South, the beginning of the Ionic lithosphere sinking accelerates the slab-retreat process in the Southern Tyrrhenian area and causes significant changes in the kinematic evolution of the upper plate. The Lazio-Abruzzi segment (3), included in the Northern Arc polygon during the previous phase, outlines a new polygon, together with the Molisan area and a small part of the accretionary wedge of the Calabrian Arc (5). The new polygon interposed between the Northern Arc and the Calabrian Arc will constitute the Southern Apennine (4). At the same time in the Tyrrhenian area starts the formation of

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Figure 3.6 Plate reconstruction of the western Mediterranean region at 12 Ma. The Tuscan-Emilian sector (1) is shown in dark gray; the Northern Arc (2) is in dark green; the Calabrian Arc (5) is in pink, the Sicilian Chain is in light green. Dotted areas are in extension (see Fig. 3.9 for the legend). M-A, Marnoso-Arenacea; M-S, Molise-Sannio. Other symbols are the same from Fig. 3.5.

the Vavilov basin (Fig. 3.7). Its triangular shape and the fanshaped slopes of its margin toward the Apennine constitute important kinematic indicators to determine the rotation of the Southern Apennine polygon (4). The anticlockwise rotation of this polygon forms the Vavilov basin. The Southern Apennine Chain (4) is constituted of exhumed units from the Calabrian accretionary wedge, which derive from the Panormide platform and from the Ionic oceanic cover (Lagonegro units). The enormous extension that generated the exhumation process is the result of the relative motion between the upper portion (5) and the basal portion (4) of the accretionary wedge. The exhumed units converge toward the Apulian domain forming the Southern Apennine Chain. At the northern boundary of the Southern Apennines polygon, the new kinematic of the Lazio-Abruzzi Apennine forms the Ancona-Anzio line (3). It is characterized by a dextral transpression that, breaking the Adriatic trench, gives rise to a TTT triple junction, in whose vertex, on the Adriatic lower plate, the Laga Basin (LB) is formed (Fig. 3.8).

43

44

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Figure 3.7 Plate reconstruction of the western Mediterranean region at 7 Ma. The Southern Apennine sector (4) is shown in light blue. Black arrows are the velocity vectors. Black lines are the meridian of the Euler poles and numbers are the coordinates. Black circle is the Euler pole of the Southern Apennine. Dotted areas are in extension (see Fig. 3.9 for the legend). CB, Caltanissetta Basin. Other symbols are the same from Fig. 3.5.

At 3 Ma, the end of the Vavilov basin extension sets the beginning of the Phase IV (Fig. 3.8). The RRR (Ridge-Ridge-Ridge) triple junction of the Southern Tyrrhenian jumps eastward, along the Apennine margin, in an area extremely extended during the two previous phases (Fig. 3.8). The southern branch of the triple junction forms the Marsili basin (Fig. 3.9), while along the eastern branch the Lagonegro Units exhumation continues. During this phase, the Ancona-Anzio line stops its activity, while the Adriatic trench jumps East of the Montagna dei Fiori and Maiella Massif, up to the Ortona-Roccamonfina line (Fig. 3.9). In the central area of the chain, the northern portion of the Lazio-Abruzzi segment (3) is again incorporated into the Northern Arc (2) polygon. The Ortona-Roccamonfina line, from this moment, forms the new boundary between the Northern Arc (2) and the Southern Apennine (4). The line ends North of the Roccamonfina volcano (Fig. 3.9) from where it transfers a convergent movement to the southern tip of the Ancona-Anzio line, through an articulated dextral transtensive structure. The structure, oriented toward

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

45

Figure 3.8 Plate reconstruction of the western Mediterranean region at 3 Ma. Dotted areas are in extension (see Fig. 3.9 for the legend).

E-W, runs along the Latina Valley where the eruptive centers of the Ernici Mounts are located. During the upper Pleistocene, the triple junction of the Southern Tyrrhenian abandons the area of the Marsili and jumps near the Aeolian Arc (Fig. 3.9). The slab-retreat process from this moment is exclusively guided by the Ionian slab.

Reconstruction of the subducted lower plate For the subducted lower plate, one of the more reliable data is reported in Schettino and Turco (2011). In this work is represented the Continent Ocean Boundary (COB) that has been traced doing the Pangea fit in the global rotation model. The trend of the various steps that made up the COB was assumed to be orthogonal to the fracture zones determined by the rotation model. The fracture zones are E-W trending in actual coordinates. The same trend can be extrapolated to the transfer faults that linked the rift basins during the Jurassic. During the AdriaEurasia collision (Late Cretaceous), the Jurassic transfer faults have been reactivated, and they cut the entire post-rift succession on the Apulian platform.

46

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Figure 3.9 Plate reconstruction of the western Mediterranean region at 0 Ma. Triangles are volcanoes: the Tuscan province is in filled in yellow, the Roman province is in orange, the Campanian province is in blue, the Aeolian Arc with Marsili and Palinuro is in black. Dotted areas are in extension (see this figure for the legend). A-A, Ancona-Anzio; AB, St. Arcangelo Basin; KB, Crotone Basin; MF, Montagna dei Fiori; PB, Paola Basin; SB, Sibari Basin; TL, Taormina Line. Other symbols are the same from Fig. 3.5.

The trend of the Apulian-Ionian COB is instead represented by the WNW-ESE trending Apulian slope that, in the rotation model, was the fracture zone during the Middle-Triassic rifting. Fig. 3.10 shows the reconstruction at 33.1 Ma of the western Tethys, where the Adriatic and Ionian COBs, with the relative synthetic isochrones and fracture zones, are represented. All this allows to determine the quantity of continental lithosphere that has been involved in the Adriatic-Ionian slab.

Geometric evolution of the Ligurian-Ionian slab Methods Considering that the tectonic setting of the upper plate, in a context of slab retreat, is governed by the slab, it should reflect the geometry of the lower plate. For instance, the oceanic trench, the accretionary wedge, the back-arc extension, and the volcanic

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

47

Figure 3.10 Plate reconstruction of the western Mediterranean region at 33.1 Ma. The Jurassic extension of the continental lithosphere is shown in light blue; dark blue is the Middle-Triassic extension. Modified from Schettino, A., Turco, E., 2011. Tectonic history of the western Tethys since the late Triassic. GSA Bull. 123 (1e2), 89e105. https://doi.org/ 10.1130/B30064.1.

arc provide clear elements to determine, with good approximation, the geometry of the lower plate, even in the absence of deep earthquake data. However, when the structures of the upper plate are complex, as in the Tyrrhenian-Apennine system, where the typical associations of the slab-retreat process are not attributable to a single continuous slab, it becomes difficult to identify the parameters that are necessary to determine the geometry of the lower plate. To determine the geometry and the evolution of the slab, in this chapter, we propose a method based on the research of the causes that determined the kinematic parameters of the tectonic setting of the upper plate. The method involves integration of the upper plate kinematic reconstruction with the structural and compositional features of the subducted lower plate (COB, fracture zone trends). The usedeupper plate kinematic reconstruction is the one described above, proposed by Turco et al. (2013). The features of subducted lithosphere are those of Schettino and Turco (2011). Finally, the features of the Adriatic-Ionian plate have been traced on the lower plate paleo maps, in the cartoon sequence of the upper plate evolution model (Figs. 3.5e3.9). This type of representation allows visualization, in the various steps of evolution, of the quantity of continental lithosphere subducted, which determines the sinking velocity into the upper mantle.

48

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Figure 3.11 Ligurian-Ionian slab geometric reconstruction. The slabs are numbered from 1 to 6. Black dotted lines are tear faults, listed from a to h. The entire slabs length is not represented.

From a careful analysis of the cartoon of the TyrrhenianApennine system evolution, it is possible to observe that, due to the articulation of the Adriatic COB line, the continental lithosphere begins to subduct starting from the North and proceeds to the South with time intervals determined by the length of the COB steps (Fig. 3.5). The slab segment that begins to include continental lithosphere progressively decreases its sinking rate until the buoyancy equilibrium is reached, while the slab portion to the South, without or with less continental lithosphere, keeps sinking into the upper mantle. The slab tear fault is produced where the sinking velocity is changing between two neighboring sectors. The tear fault propagates along the trend of fracture zones and transforms faults generated during the breakup of Pangea. This type of process spreads toward the South, following the steps of the Adriatic COB. The segmented geometry of the Ligurian-Ionian slab, generated by the described process, is represented in Fig. 3.11.

Ligurian-Ionian slab evolution In the initial phase of opening of the Tyrrhenian basin (19e12 Ma), the separation of the Proto-Apennine Arc from the Western Alps Arc originates an E-W trending sinistral transcurrent fault (Emilian fault of Bosellini, 1981) along which, during its growth, the Ligurian Alps and the Tuscan-Emilian sector of the Apennine Chain (1) develop. To the South, the Tyrrhenian

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

extension ends with a dextral transform fault, through the channel of Sardinia. Between the two transform faults (in yellow in Fig. 3.6), the Adriatic-Ionian trench develops, which outlines a slab bounded to the North and South by tear faults. The tear fault to the North (a, in Fig. 3.11) propagates along the transfer structure of the Jurassic rifting that separated the lithosphere of the Ligurian basin from the Adriatic continental one. On the upper plate, the Adriatic slab tear fault detachment is reflected on the Ligurian-Tuscan-Emilian (1) segment of the chain. In this phase, the curvature radius of the Apennine trench, still sufficiently large, suggests a continuous Adriatic-Ionian slab from North to South, mainly constituted by oceanic lithosphere. During phase II (7e12 Ma), sinking velocity of the northern portion of the Adriatic slab slows, due to the subducted continental lithosphere, which increases its buoyancy (slab 1 of Fig. 3.11). With this event, the tear fault (b) is activated and, propagating along a Jurassic discontinuity, separates two slab portions with different sinking rates. The separation between the TuscanEmilian sector (1) and the Northern Arc (2) begins, clearly distinct from their kinematic of extension. The boundary along the two sectors runs along the Apuan Alps-Gabicce alignment, E-W trending, and represents the reflection of the tear fault (b) on the upper plate. At the end of this phase, the Adriatic-Ionian slab is still continuous South of the tear fault (b) up to the channel of Sicily. During phase III (7e3 Ma), the Vavilov basin formation and the activation of the Ancona-Anzio line, both caused by the Southern Apennine rotation around its Euler pole, located inside the same polygon, and mark a deep change in the kinematics of the Apennine Chain. The cause is the slab geometry that evolves with the variation in buoyancy in function of the quantity of subducted continental lithosphere. Along the lines of sinking rate variation, new tear faults are activated, separating the slab in segments with different buoyancy. The slab fragmentation is propagated toward South up to the tear fault (e). The sectors 5e6 of the slab, still joined during this phase, is essentially composed by oceanic Ionian lithosphere, which gives this sector a remarkable sinking velocity. The substantial difference in velocity, increasing toward the southern sectors of the slab, causes the anticlockwise rotation of the Southern Apennine polygon while the Calabrian Arc migrates toward SE, essentially driven by the Ionian portion of the slab sector 5e6. The direct evidences of these tear faults on the upper plate are not very clear, while on the lower plate (Apulia), the Jurassic structures, along which the tear faults propagated, can be identified with the Mattinata line (d) and with the 41st parallel that

49

50

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

passes through the Canal of Pyrrhus line and the Vulture Volcano (e) (Fig. 3.9). The indirect evidences are instead substantial and are represented by the implications on the kinematic of the upper plate evolution. The anticlockwise rotation of the Southern Apennine consistently reflects the evolution of the slab. This process forms the Vavilov basin, activates the transpressive Ancona-Anzio line, and forms the LB (Fig. 3.9). The phase IV (3e0 Ma) is characterized by the tear fault (f) activation. It propagates along the Middle-Triassic ApulianIonian COB and produces effects in all the TyrrhenianApennine and Calabrian Arc areas. The main effects are the rejump of the Vavilov basin extension toward East, the formation of the Marsili basin, the inclusion of the Lazio-Abruzzi sector in the Northern polygon, the activation of the OrtonaRoccamonfina line and the right transtensive movement along the Latina valley. Finally, the detachment produced by the tear fault (f) causes a consistent uplift of the axis of the Southern Apennine Chain (Cinque et al., 1993), due to the elastic rebound of segment 5 of the Apulian slab. In the last million years, the oceanic lithosphere of the Apennine slab segments begins to detach from the continental lithosphere. Probably, the slab 3 is completely detached, as witnessed by the general uplift of the Lazio-Abruzzi Chain (Galadini et al., 2003). Southward the tear fault (g) starts to propagate along the tear fault (h) (Malta Escarpment, ME in Fig. 3.9). The direct evidences on the upper plate of the latter tear fault are not always clear. They are probably hidden by the great extension between the Calabrian Arc and the Southern Apennine that exhumes the Lagonegro deposits. However, the Ionian slab is the only well-defined Benioff zone throughout the Tyrrhenian area.

Conclusions and implication on the Campanian magmatism The evolution of the Tyrrhenian-Apennine system (upper plate) is generated by the slab-retreat process and driven by the fragmentation of the Adriatic-Ionian slab. In the first phase of its evolution, the extension produced by the sinking of the Apennine slab with western polarity separates the Proto-Apennine Chain and the Calabrian Arc from the Sardinia-Corsica block. The Eastward migration of the chain produces extension along the trench and fragments the chain into four sectors. The boundary between the sectors is marked by top wedge basins.

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

The different amount of subducted continental lithosphere along the slab causes different sinking rates that generate tear faults. The slab begins to fragment in segments starting from the North. The fragmentation of the Adriatic slab generates a mosaic of microplates on the upper plate, distinguished by their kinematics of extension. The formation of the Vavilov basin sets the beginning of the Ionian lithosphere subduction, which rearranges the mosaic of the microplates. The Southern Apennine, exhumed from the Calabrian accretionary wedge, is added to this configuration. Later, the tear faults along the COB between the Ionian and the Apulian lithosphere activates. At the same time, the extension of the Vavilov basin ceases and activates in the Marsili basin. The reconstruction of the slab geometry in the context of its temporal evolution provides us with useful elements to understand the geodynamic context in which the magmatic sources of the Tyrrhenian-Apennine Area are located. This area, based on magma compositions, has historically been divided into Magmatic Provinces from which the geodynamic contexts responsible for the contamination of the magmatic sources have been extrapolated (Peccerillo, 2019, this volume). From the geodynamic point of view, magmatism can be divided according to the position of the sources in the tectonic context, but there is not always a clear correlation with magma composition. However, as described by Peccerillo (2019, this volume), all of the magmatism in Central Italy (from Tuscany to the Aeolian Islands) shows geochemical indications of source regions metasomatized by subduction processes (fluids and subducted terrigenous to marly sediments), superimposed on original mantle components that vary from Mid-Ocean Ridge Basalts (MORB)elike to Ocean Island Basalt (OIB)elike. From the slab geometry represented in Fig. 3.12, deduced from the kinematics that produced the evolution of the upper plate, it is possible to distinguish classic volcanic arc sources as the Aeolian Arc, located above the Ionian slab; sources located above the Apennine slab, which includes Tethys oceanic lithosphere, with its transition to Adriatic continental lithosphere (Roman Province); and oceanic type (MORB) sources as the Vavilov and Marsili. In addition, there are centers of volcanic activity located near the vertical projection of the tear faults whose sources, probably located in the asthenosphere of the lower plate, are contaminated by the adjacent slab segment, in a rearward position. The best example is represented by the magmatism of the Campanian

51

52

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Figure 3.12 Ligurian-Ionian slab geometric reconstruction with upper plate structures. See Fig. 3.11 for other symbols.

plane, placed on the vertical projection of a particular asthenospheric window (Fig. 3.12). On the same vertical, the segment 5 of the slab, made of only Apulian continental lithosphere, undergoes a significant elastic rebound due to the tear fault detachment of the Ionian lithosphere. This event generates an asthenospheric upwelling, with slab retreat perhaps pulling in mantle from farther West, and creates the ideal conditions for the production of magma that characterizes the Campania Plain. Isotopic data summarized by Peccerillo (2019, this volume and references therein) suggest that the mantle underlying the Campi FlegreieVesuvius, while clearly influenced by subduction metasomatism, is most similar to mantle source regions for the eastern Aeolian Islands (e.g., Stromboli) and Vulture but quite different from the mantle source regions for Roman and Tuscan magmatism to the North and also distinct from mantle beneath the Western Aeolian Islands and Etna. Finally, to simplify the comprehension of the magmatism linked to the Apennine subduction, it is important to clarify the geodynamic significance of the Tuscan magmatic province. The magmatism of this province is much older than that associated with the Apennine subduction. From a compositional point of view, it is part of a collisional context with substantial involvement of continental basement in the subduction. The magmatism associated with the Apennine subduction forms instead in a context of slab retreat in which the continental collision is

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

not contemplated. The magmatism of the Tuscan province is located only in the area in front of the Alpine Corsica. From the available data, we believe that the Apennine slab only created the conditions for the melting of the asthenosphere, already contaminated by the Alpine Corsica continental collision, which had a subduction with an eastward polarity during the Upper Oligocene (Turco et al., 2012).

Acknowledgments Many thanks to Crescentini L. and Ripepe M. for their careful reviews and to Peccerillo A. and Carroll M.R. for useful discussions.

References Argnani, A., 2012. Plate motion and the evolution of Alpine Corsica and Northern Apennines. Tectonophysics 579, 207e219. Biju-Duval, B., Dercourt, J., Le Pichon, X., 1977. From the Tethys Ocean to the Mediterranean Seas: a plate tectonic model of the evolution of the Western Alpine system. In: Biju-Duval, B., Montadert, L. (Eds.), International Symposium on the Structural History of the Mediterranean Basins (Split, 1976). Editions Technip, Paris, pp. 143e164. Boccaletti, M., Ciaranfi, N., Cosentino, D., Deiana, G., Gelati, R., Lentini, F., Massari, F., Moratti, G., Pescatore, T., Lucchi, F.R., Tortorici, L., 1990. Palinspastic restoration and paleogeographic reconstrution of the perithyrrenian area during the Neogene. Palaeogeogr. Palaeoclimatol. Palaeoecol. 77, 41e50. Bosellini, A., 1981. The Emilia fault: a Jurassic fracture zone that evolved into a Cretaceous-Paleogene sinistral wrench fault. Boll. Soc. Geol. Ital. 100, 161e169. Brandmayr, E., Raykova, R.B., Zuri, M., Romanelli, F., Doglioni, C., Panza, G.F., 2010. The lithosphere in Italy: structure and seismicity. In: Beltrando, M., Peccerillo, A., Mattei, M., Conticelli, S., Doglioni, C. (Eds.), Journal of the Virtual Explorer, vol. 36. Paper 1. Carmignani, L., Decandia, F.A., Disperati, L., Fantozzi, P.L., Lazzarotto, A., Liotta, D., Oggiano, G., 1995. Relationships between the tertiary structural evolution of the Sardinia-Corsica-Provencal domain and the Northern Apennines. Terra Nova 7 (2), 128e137. Cesarano, M., Pierantoni, P.P., Turco, E., 2002. Structural analysis of the Albidona Formation in the Alessandria del Carretto-Plataci area (CalabroLucanian Apennines, southern Italy). Boll. Soc. Geol. Ital. 1, 669e676. Cinque, A., Patacca, E., Scandone, P., Tozzi, M., 1993. Quaternary kinematic evolution of the Southern Apennine. Relationships between surface geological features and deep lithospheric structures. Sec. Issue on the Workshop: “Modes of crustal deformation: from the brittle upper crust through detachments to the ductile lower crust” (Erice, 18e24 November 1991). Ann. Geofisc. 36, 249e260. Dercourt, J., Zonenshain, L.P., Ricou, L.E., Kazmin, V.G., Le Pichon, X., Knipper, A.L., Grandjacquet, C., Sbortshikov, I.M., Geyssant, J., Lepvrier, C., Pechersky, D.H., Boulin, J., Sibuet, J.-C., Savostin, L.A., Sorokhtin, O., Westphal, M., Bazhenov, M.L., Lauer, J.P., Biju-Duval, B., 1986. Geological

53

54

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

evolution of the Tethys belt from the Atlantic to the Pamirs since the Lias. Tectonophysics 123, 241e315. Dewey, J.F., Helman, M.L., Turco, E., Hutton, D.H.W., Knott, S.D., 1989. Kinematics of the Western Mediterranean. In: Coward, M.P., Dietrich, D., Park, R.G. (Eds.), Alpine Tectonics, vol. 45. Geol. Soc. Spec. Publ., pp. 265e283 Doglioni, C., Gueguen, E., Harabaglia, P., Mongelli, F., 1999. On the origin of west-directed subduction zones and application to the western th, S. (Eds.), The Mediterranean Basins: Mediterranean. In: Durand, J., Horva Tertiary Extension within the Alpine Orogen, vol. 156. Geological Society of London, pp. 541e561. Doglioni, C., 1991. A proposal of kinematic modelling for W- dipping subductions- Possible applications to the Tyrrhenian-Apennines system. Terra Nova 3, 423e434. Faccenna, C., Davy, P., Brun, J.-P., Funiciello, R., Giardini, D., Mattei, M., Nalpas, T., 1996. The dynamics of backarc extensions: an experimental approach to the opening of the Tyrrhenian Sea. Geophys. J. Int. 126, 781e795. Faccenna, C., Becker, T.W., Lucente, F.P., Jolivet, L., Rossetti, F., 2001. History of subduction and back-arc extension in the Central Mediterranean. Geophys. J. Int. 145, 809e820. Faccenna, C., Becker, T.W., Auer, L., Billi, A., Boschi, L., Brun, J.P., Capitanio, F.A., Funiciello, F., Horvàth, F., Jolivet, L., Piromallo, C., Royden, L., Rossetti, F., Serpelloni, E., 2014. Mantle dynamics in the Mediterranean. Rev. Geophys. 52 (3), 283e332. Ferranti, L., Oldow, J.S., Sacchi, M., 1996. Pre-quaternary orogen-parallel extension in the Southern Apennine Belt, Italy. Tectonophysics 260, 325e347. Galadini, F., Messina, P., Sposato, A., 2003. Early uplift of the Abruzzi Apennines (central Italy): avaliable geomorphological constraints. Quaternary International 101e102, 125e135. Jolivet, L., Faccenna, C., 2000. Mediterranean extension and the Africa-Eurasia collision. Tectonics 19, 1095e1107. Kastens, K.A., Mascle, J., et al., 1987. Proc Ocean Drilling Program Init Reports 107, p. 772. Lavecchia, G., Federico, C., Stoppa, F., Karner, G., 1995. La distensione toscotirrenica come possibile motore della compressione appenninica. Studi Geol. Camerti 489e497 vol. spec. Malinverno, A., Ryan, W.B.F., 1986. Extension in the Tyrrhenian Sea and shortening in the Apennines as result of arc migration driven by sinking of the lithosphere. Tectonics 5, 227e245. Mantovani, E., Viti, M., Albarello, D., Babbucci, D., Tamburelli, C., Cenni, N., 2002. Generation of backarc basins in the Mediterranean region: driving mechanisms and quantitative modelling. Boll. Soc. Geol. Ital. 1, 99e111. Marani, M.P., Gamberi, F., 2004. Structural framework of the Tyrrhenian Sea unveiled by seafloor morphology. Mem. Descr. Carta Geol. D’Ital. 64, 97e108. Marani, M.P., 2004. Super-inflation of a spreading ridge through vertical accretion. Mem. Descr. Carta Geol. D’Ital. XLIV, 185e194. Milia, A., Torrente, M.M., 1999. Tectonics and stratigraphic architecture of a periTyrrhenian half-graben (Bay of Naples, Italy). Tectonophysics 315, 301e318. Milia, A., Torrente, M.M., 2014. Early-stage rifting of the Southern Tyrrhenian region: the CalabriaeSardinia breakup. J. Geodyn. 81, 17e29. Nicolich, R., 1981. Crustal structures in the Italian Peninsula and surrounding seas: a review of DDS data. In: Wezel, F.C. (Ed.), Sedimentary Basins of the

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Mediterranean Margins. C.N.R. Italian Project of Oceanography. Tectoprint, Bologna, pp. 489e501. Panza, G.F., Calcagnile, G., 1979/1980. The upper mantle structure in Balearic and Tyrrhenian bathyal plains and the Messinian salinity crisis. Palaeogeogr. Palaeoclimatol. Palaeoecol. 29, 3e14. Panza, G.F., 1984. Structure of the lithosphereeasthenosphere system in the Mediterranean region. Ann. Geophys. 2, 137e138. Patacca, E., Scandone, P., 2001. Late thrust propagation and sedimentary response in the thrust-belt-foredeep system of the Southern Apennines (Pliocene-Pleistocene). In: Vai, G.B., Martini, I.P. (Eds.), Anatomy of an Orogen: The Apennines and Adjacent Mediterranean Basins. Kluwar Academic Publishers, Dordrecht, The Netherlands, pp. 401e440. Patacca, E., Scandone, P., 2007. Geology of the Southern Apennines. Boll. Soc. Geol. Ital. (Ital. J. Geosci.) (7), 75e119, 14 figs., CROP-04 (ed. by A. Mazzotti, E. Patacca and P. Scandone). Patacca, E., Sartori, R., Scandone, P., 1990. Tyrrhenian basin and Apenninic arcs: kinematic relations since late Tortonian times. Mem. Soc. Geol. Ital. 45, 425e451. Peccerillo, A., Turco, E., 2004. Petrological and geochemical variations of PlioQuaternary volcanism in the Tyrhhenian Sea area: regional distribution of magma types, petrogenesis and geodynamic implications. Per. Mineral. 73, 231e251. Peccerillo, A., 2019. Campanian volcanoes: petrology, geochemistry and geodynamic significance. In: De Vivo, B., Belkin, H.E., Rolandi, G., Vesuvius (Eds.), Campi Flegrei, and Campanian Volcanism (This volume). Rosenbaum, G., Lister, G.S., 2004. Neogene and quaternary rollback evolution of the Tyrrhenian Sea, the Apennines, and the Sicilian Maghrebides. Tectonics 23, TC1013. https://doi.org/10.1029/2003TC001518. Rosenbaum, G., Lister, G.S., Duboz, C., 2002. Reconstruction of the tectonic evolution of the western Mediterranean since the Oligocene. J. Virtual Explor. 8, 107e126. Sartori, R., Torelli, L., Zitellini, N., Carrara, G., Magaldi, M., Mussoni, P., 2004. Crustal features along a WeE Tyrrhenian transect from Sardinia to Campania margins (Central Mediterranean). Tectonophysics 383, 171e192. Sartori, R., 1990. The main results of ODP leg 107 in the frame of neogene to recent geology of perityrrhenian areas. In: Kastens, K., Mascle, J., et al. (Eds.), Proc Ocean Drilling Program Sci Results, vol. 107, pp. 715e730. Sartori, R., 2003. The Tyrrhenian back-arc basin and subduction of the Ionian lithosphere. Episodes 26 (3), 217e221. Schettino, A., Turco, E., 2006. Plate kinematics of the Western Mediterranean region during the Oligocene and Early Miocene. Geophys. J. Int. 166 (3), 1398e1423. Schettino, A., Turco, E., 2009. Breakup of Pangaea and plate kinematics of the central Atlantic and Atlas regions. Geophys. J. Int. 178 (2), 1078e1097. https://doi.org/10.1111/j.1365-246X.2009.04186.x. Schettino, A., Turco, E., 2011. Tectonic history of the western Tethys since the Late Triassic. GSA Bull. 123 (1e2), 89e105. https://doi.org/10.1130/B30064.1. Schettino, A., 1998. Computer-aided paleogeographic reconstructions. Comput. Geosci. 24, 259e267. Scrocca, D., Doglioni, C., Innocenti, F., 2003. Constraints for an interpretation of the Italian geodynamics: a review. Mem. Descr. Carta Geol. D’Ital. LXII, 15e46.

55

56

Chapter 3 Kinematics of the Tyrrhenian-Apennine system and implications

Selli, R., 1981. Thoughts on the geology of the Mediterranean region, Sedimentary Basins of Mediterranean Margins. C.N.R. Italian Project of Oceanography, pp. 489e501. Spadini, G., Cloething, S., Bertotti, G., 1995. Thermo-mechanical modelling of the Tyrrhenian Sea: lithosphere necking and kinematics of rifting. Tectonics 14, 629e644. Turco, E., Zuppetta, A., 1998. A kinematic model for the Plio-Quaternary evolution of the TyrrhenianeApenninic system; implications for rifting processes and volcanism. J. Volcanol. Geotherm. Res. 82, 1e18. Turco, E., Macchiavelli, C., Mazzoli, S., Schettino, A., Pierantoni, P.P., 2012. Kinematic evolution of the Alpine Corsica in the framework of Mediterranean mountain belts. Tectonophysics 579, 193e206. Turco, E., Schettino, A., Macchiavelli, C., Pierantoni, P.P., 2013. A plate kinematics approach to the tectonic analysis of the Tyrrhenian-Apennines System. Rend. Online Soc. Geol. Ital. 29, 187e190. Zuppetta, A., Mazzoli, S., 1995. Analisi strutturale ed evoluzione paleotettonica dell’Unità del Cilento nell’Appennino Campano. Studi Geol. Camerti 13, 103e114. Zuppetta, A., Mazzoli, S., 1997. Deformation history of a synorogenic sedimentary wedge, northern Cilento area, southern Apennines thrust and fold belt, Italy. GSA Bull. 109, 698e708. Zuppetta, A., Russo, M., Turco, E., Gallo, L., 1984. Età e significato della Formazione di Albidona in Appennino Meridionale. Boll. Soc. Geol. Ital. 103, 159e170.

4 Lithosphere structural model of the Campania Plain Concettina Nunziata,1 Maria Rosaria Costanzo,1 Giuliano Francesco Panza2, 3, 4 1

Department of Earth Sciences, Environment and Resources, University of Naples Federico II, Italy; 2Emeritus Honorary professor China Earthquake Administration (CEA), Beijing, China; 3Honorary professor Beijing University of Civil Engineering and Architecture (BUCEA), Beijing, China; 4Accademia Nazionale dei Lincei & Accademia Nazionale dei XL, Rome, Italy

Introduction The Campania Plain is bordered in the north and south by volcanic edifices, by the Tyrrhenian Sea in the west and by Southern Apennines in the east (Fig. 4.1). The quiescent Roccamonfina volcano is in the north, the active Mt. Vesuvius volcano is in the south-east, the active Campi Flegrei and Ischia Island and the quiescent Procida Island are in the south-west. It formed during Pleistocene, like several other basins, when extensional tectonics affected the Campania margin and the western flank of the Southern Apennines, mainly controlled by NW-SE and NE-SW normal faults (Vitale and Ciarcia, 2018 and references therein). It has been the site of past volcanic activity as testified by lava bodies (about 2 Ma) with calcalkaline affinity found in deep drillings (Fig. 4.2). The Campania Magmatic Province (about 0.2 Ma to 1944 AD) consists of stratovolcanoes and multicentre volcanic complexes (Mt. Vesuvius, Campi Flegrei, ProcidaVivara, Ischia) that are built up by mafic to felsic alkaline potassic magmas (Peccerillo, 2017 and references therein). Leucitebearing ultrapotassic rocks are restricted to Somma-Vesuvius, also deriving from trachybasalt, but with extensive carbonate assimilation. The rocks of the Campania Province define various suites that have been generated by polybaric fractional crystallization, mixing, and assimilation of different types of wall rocks, starting from trachybasalt parents. Vesuvius, Campi Flegrei, and Campanian Volcanism. https://doi.org/10.1016/B978-0-12-816454-9.00004-3 Copyright © 2020 Elsevier Inc. All rights reserved.

57

58

Chapter 4 Lithosphere structural model of the Campania Plain

Figure 4.1 Simplified geological map of the Campania region with location of deep drillings (http://unmig.mise.gov. it/videpi/videpi.asp; Ippolito et al., 1973). Modified after Costanzo, M.R. and Nunziata, C., 2014. Lithospheric VS models in the Campanian Plain (Italy) by integrating Rayleigh wave dispersion data from noise cross-correlation functions and earthquake recordings. Phys. Earth Planet. Inter 234 46e59. https://doi.org/10.1016/j.pepi.2014.05.002.

The buried volcanism beneath the Campania Plain is a remnant of a temporal transition from calcalkaline to potassicultrapotassic magmatism in the Campania area. A similar evolution has been observed at Stromboli, where early calcalkaline activity has been followed by shoshonitic and potassic alkaline magmatism. In the last years, some authors (e.g., De Vivo et al., 2001; Rolandi et al., 2003) have reached the conclusion that a significant volcanic source should be located in the Campania Plain. This conviction is based on the recognition of numerous trachytic ignimbrite deposits, which are older and younger than the Campanian Ignimbrite (CI) eruption (39 ka after De Vivo et al., 2001). The CI eruption was a huge explosive event that deposited

Chapter 4 Lithosphere structural model of the Campania Plain

Figure 4.2 Stratigraphies of the deep wells (numbers 1-7 in Fig. 4.1).

a large volume (w150e200 km3) of trachytic-phonolitic material, distributed over w 30,000 km2 (for a review, see De Vivo et al., 2010). In addition, the widespread distribution of proximal lithic breccia deposits associated with the ignimbrite over the entire Campania Plain has suggested that CI originated from a fracture’s system linked with the subsidence of the Campania Plain. Information about the lithospheric (crust and uppermost mantle) properties is of paramount importance to locate the main sources of magmas erupted at the surface. It can be obtained by geophysical investigations, petrological and geochemical studies of magmas and of high-pressure xenoliths entrained in volcanic rocks. Most of the models of the Earth interior are based on single sets of either geophysical or petrological data, whereas integrated petrological, geochemical and geophysical studies can give the maximum information (e.g., Peccerillo and Panza, 1999). In this chapter, the state of the art on the lithospheric models of the Campania Plain is reviewed. The starting point is the cellular (1
 1
model of the lithosphereeasthenosphere system (LAS) of the Italian area and surrounding regions combined with petrological and geochemical studies, which significantly contributed to shed some light in the debate on the geodynamic

59

60

Chapter 4 Lithosphere structural model of the Campania Plain

evolution of the area (e.g., Panza et al., 2007a,b; Brandmayr et al., 2010). The integration of the regional surface wave dispersion data with the local ones (e.g., Costanzo and Nunziata, 2014, 2017) has given an important contribution to the definition of crust and upper mantle structural models.

Regional lithospheric models Lithospheric structure information for Italy and surroundings is available from models obtained for 1
 1
cells by the nonlinear inversion with Hedgehog method of fundamental-mode Rayleigh wave dispersion data (Panza et al., 2007a and references therein) (Fig. 4.3). The available dispersion data, both phase velocities, determined by the two-station method (Panza, 1976), and group velocities, measured by the frequencyetime analysis (Levshin et al., 1989), have been used to obtain two-dimensional tomography maps (Yanovskaya, 2001, and references therein). The cellular dispersion data, spanning in the ranges from 7 s to 150 s for group velocities and from 15 s to 150 s for phase velocities, have allowed to obtain reliable velocity structure in

Figure 4.3 Map of Italy and surroundings modeled by 1
 1
cells in which VS models have been defined (Brandmayr et al., 2010). The interpretative cross sections 1 (CS1) and 2 (CS2) are also located.

Chapter 4 Lithosphere structural model of the Campania Plain

the depth range from 3-13 km to about 350 km (Brandmayr et al., 2010). In each cell, in the inversion of dispersion values, the structure of Earth has been modeled down to the depth of about 600 km. In the uppermost layers, 3e13 km thick depending on the lower limit of the period range of the cellular dispersion curves, the mechanical properties are fixed a priori, using independent literature information specific for each cell. In the subjacent layers, P- and S-wave velocities (VP, VS), density, and thicknesses are variable, while in the last bottom parameterized layer, VP, VS, and density are fixed and the thickness varies in such a way that the whole stack of layers has a total thickness of 350 km. The structure below 350 km has been taken from the average model for the whole Mediterranean, EurID database, of Du et al. (1998). When the cell is located in a sea region, the thickness of the water layer and of the sediments is taken into account. For each cell, all the solutions have been processed with an optimized smoothing method (Boyadzhiev et al., 2008) with the aim to define a smooth 3D model of the LAS. The obtained representative cellular models have been appraised and constrained using independent studies (Brandmayr et al., 2010, 2011). Moreover, the Moho boundary based on shear wave velocities (Fig. 4.4) has been located by using the depth distribution of the seismic events collected by ISC (International Seismological Center, http://www.isc.ac.uk/) with magnitude M  3 (1904e2006) as an additional criterion when its identification was not straightforward (Panza and Raykova, 2008).

The lithosphereeasthenosphere system under the Campania Plain Several definitions are used in the description of the VS structures: (i) lithospheric mantle (LID); (ii) soft mantle lid; (iii) asthenospheric low-velocity zone (LVZ); and (iv) mantle wedge. The LID is the portion of the mantle with high seismic wave velocity (VP between 7.5 and 8.6 km/s; VS generally higher than 4.35 km/s and lower than 4.9 km/s) and high density (between 3.0 g/cm3 and 3.4 g/cm3). It still has brittle behavior. The soft mantle lid is a layer of lithospheric mantle material, right below the Moho discontinuity, partially molten, with low VS and relatively high-density values. The origin of this high-percentage melt layer is neither limited nor directly bound to subduction areas (VP between 6.9 km/s and 8.2 km/s; VS lower than 4.35 km/s; density between 3.0 g/cm3 and 3.3 g/cm3). The LVZ is an asthenospheric

61

62

Chapter 4 Lithosphere structural model of the Campania Plain

Figure 4.4 Moho depth determined by 1


 1
cellular VS models (Brandmayr, 2012).

layer with low seismic wave velocities; it is present right below the LID or deeper, under faster asthenospheric layers (VP between 7.9 and 8.6 km/s; VS between 4.0 km/s and 4.4 km/s; density between 3.1 g/cm3 and 3.5 g/cm3). The mantle wedge is the portion of mantle material found between a subducting slab and the overriding lithosphere where plastic deformation occurs. In this region, according to Van Keken (2003), hydrothermal uprising flow causes partial melting of subducting slab material due to dehydration. The cellular VS models (Brandmayr et al., 2010) and the 3D density models (Brandmayr et al., 2011), obtained by using as fixed (a priori) information the layering of the cellular VS models, show a clear picture of the main geological and tectonic features of Italy territory and surroundings. Assuming the density value of 3.0 g/cm3 as the conventional threshold between crust and mantle material, a general agreement is found between the Moho depths inferred from the density model and the VS model.

Chapter 4 Lithosphere structural model of the Campania Plain

Asymmetric features in the velocity and density models have been observed between northern and Southern Tyrrhenian basin, with a longitudinal axis roughly corresponding to the 41
N parallel. The southern (active) part of the basin is generally characterized by mantle velocities that are lower and mantle densities that are higher than those in its northern part. Asymmetry is evidenced between E-verging Dinaric and W-verging Apenninic subduction zones, which supports the hypothesis of an eastward mantle flow, especially in the LVZ. The flow is very shallow in the active Tyrrhenian basin where an anomalous LVZ is detected just below the Moho, with VS generally less than 4.20 km/s (Brandmayr et al., 2010). Furthermore, slabs are not denser than the ambient mantle, but they appear to be slightly lighter below all subductions zones, which conflicts with the concept of slab pull and thus calls for different actors in subduction dynamics such as upper-mantle convection, Earth’s rotation, and lateral heterogeneities in the viscosity contrast at the lithosphereeasthenosphere boundary (Brandmayr et al., 2011; Doglioni and Panza, 2015). Campania Plain is mainly contained by cells a4 and A4 and bordered by cells a3 and A3 (Figs. 4.3 and 4.5). Cell a3, containing Roccamonfina volcano, is characterized by a crust about 25 km thick lying on a soft mantle layer (VS about 4.20 km/s), which extends down to about 50 km depth, where asthenospheric material is likely to be present (VS about 4.35 km/s). In cell a4, centered in the Molise Apennines, the crust is about 40 km thick and lies on a lid layer (VS about 4.45 km/s), which reaches a depth of about 90 km, where the top of asthenosphere is likely to be located (VS about 4.40 km/s). Cell A4, containing Neapolitan volcanoes, is characterized by about 23 km thick crust lying on a soft mantle layer (VS about 4.2 km/s), which extends down to about 73 km depth. Below the soft mantle layer two faster layers (VS about 4.40 km/s) extend down to about 300 km depth. To the west, in the nearby cell A3 (Ischia), the crustemantle transition is rather complex and seems to be consistent or with a lithospheric doubling where the deeper Moho is at about 20 km and sits on soft mantle or with the presence of a shallow layer of consolidated magma reservoir.

The geodynamical interpretation of the lithosphereeasthenosphere system model Petrological and geochemical studies evidence the regional distribution of magma types, strong lateral variations in the

63

64

Chapter 4 Lithosphere structural model of the Campania Plain

Figure 4.5 Cellular structural model extended to 350 km depth for the Southern Tyrrhenian area, including the Campania Plain (cells a4eA4 located in Fig. 4.3). Colors represent VS in crustal layers (yellow to brown) and mantle layers (blue to violet). Red dots denote all seismic events collected by International Seismological Center with magnitude M  3 (1904e2006). For each layer, VS variability range and uncertainty on thickness (texture) are reported. Modified after Brandmayr, E., Raykova, R.B., Zuri, M., Romanelli, F., Doglioni, C., Panza, G.F., 2010. The lithosphere in Italy: structure and seismicity. In: Beltrando M., Peccerillo A., Mattei M., Conticelli S., Doglioni C. (Eds.), The Geology of Italy, Journal of the Virtual Explorer, Electronic edn, 36, paper 1 ISSN 1441e8142. http://virtual-explorer.com.au/ article/2009/224/lithosphere-structure-seismicity.

modal mineralogy of the upper mantle, and different depths of the partially melted material (Peccerillo, 2003). Major element, trace element, and isotopic data on mafic rocks suggest that the Italian volcanism can be subdivided into different magmatic provinces, which were generated by petrologically and geochemically distinct mantle sources (Peccerillo, 2017). In several cases, tectonic lines that are not limited to the crust, but involve the lithosphere as well, separate the different magmatic provinces from each other. The 41
parallel line divides the Southern Tyrrhenian Sea and the Campania Province from Ernicie Roccamonfina zone. Campania province consists of dominant potassic and ultrapotassic rocks, with calcalkaline rocks buried beneath the Campania Plain. Such evolution has been observed at Stromboli, which suggests a common type of source for the eastern Aeolian arc and the Campanian area. According to Peccerillo (this book), the hypothesis that best explains these features is that volcanoes of Campania, the eastern Aeolian arc, and Vulture are related to the contamination of a FOZO (Focus Zone)-type OIB (Ocean Island Basalt) (see, e.g., Stracke et al., 2005) mantle source by fluids released during the subduction

Chapter 4 Lithosphere structural model of the Campania Plain

process of the oceanic-type portion of the Ionian plate beneath Southern Italy, from Calabria to Campania (e.g., Orecchio et al., 2014 and references therein), with small amounts of sediments. A detailed geodynamical interpretation has been performed in the Italic region combining VS structural models with geological interpretation and correlating them with heat flow and gravimetric data (Brandmayr et al., 2010). The main geodynamical features of the Apennines and Tyrrhenian basin are well delineated by the VS cellular models: the presence of relatively high-velocity bodies along the Apennines indicates the subduction of the Adria lithosphere (Panza et al., 2007b), and the shallow crustemantle transition beneath the Tyrrhenian Sea, with extended soft mantle layers (VS< 4 km/s) just below the Moho, indicate a high percentage of melts and magmas (Panza et al., 2007a). In general, the shallow asthenosphere beneath the Tyrrhenian Sea supports the ongoing extension process associated with the eastward migration of the Apenninic subduction (Gueguen et al., 1997; Doglioni et al., 1999). Along a SW-NE trending profile (CS1 in Fig. 4.3), from Southern Sardinia to Sava Basin, that crosses the northern part of the Campania Plain (cell a4), the westward subducting Apenninic lithosphere is almost vertically bent by the mantle easterly directed flow, while the Dinaric eastward subduction has a dip angle of about 20e30
(Fig. 4.6b), as discussed in detail by Doglioni et al. (1999) and Carminati et al. (2004). A mantle wedge is evidenced in both upper plates of the Dinaric and Apenninic subductions by low velocities layers (VS w4.00 km/s and w4.20 km/s). To the west, the LVZ uprises beneath the Tyrrhenian Sea and directly feeds Tyrrhenian volcanoes as Magnaghi. A density higher than the surroundings is found in the LVZ, and the 3.3 g/cm3 density reaches depths of about 70 km in the active part of the Tyrrhenian basin where the top of the asthenosphere is very shallow (Fig. 4.6b). Therefore, higher densities in the mantle seem to be strictly related to the eastward flow itself and to its ascent beneath the back-arc basin. Relatively lowdensity mantle is seen in particular beneath the Apenninic and Dinaric subductions, which evidences that subduction is related to mantle flow and not to negative buoyancy - slab pull (Brandmayr et al., 2011; Doglioni and Panza, 2015). The considerable thickness of the LVZ may be justified by the presence of low fractions of volatile-rich melts or by fluids (Frezzotti et al., 2009). This hypothesis would support CO2 nonvolcanic emissions extended from the Tyrrhenian coast to the Apennines and leads to the interpretation of the central

65

Figure 4.6 Lithospheric model along the SW-NE profile from Southern Sardinia to Sava Basin (CS1 in Fig. 4.3). Red dots denote all seismic events collected by International Seismological Center with magnitude greater than 3 (1904e2006). (a) Top: Cellular modelsdYellow to brown colors represent VS in crustal layers, blue to violet colors indicate VS in mantle layers. For each layer, VS variability range is reported. For the sake of clarity, in the uppermost crustal layers, the values of VS are omitted. The uncertainties in the thickness are represented by texture. Bottom: Interpretation of the model. (b) VS and density model. VS distribution is given by the color scale, continuous contour lines refer to density (in g/cm3), while broken white lines delineate the lid low-velocity zone margin. The minor differences in the schematic models based on VS and density values may originate from the different smoothing optimization algorithms used by Brandmayr et al. (2010) and Brandmayr et al. (2011); the robust feature is that the slab is not denser than the ambient mantle, but it appears to be slightly lighter, which conflicts with the concept of slab pull. (a) Modified after Brandmayr, E., Raykova, R.B., Zuri, M., Romanelli, F., Doglioni, C., Panza, G.F., 2010. The lithosphere in Italy: structure and seismicity. In: Beltrando M., Peccerillo A., Mattei M., Conticelli S., Doglioni C. (Eds.), The Geology of Italy, Journal of the Virtual Explorer, Electronic edn, 36, paper 1 ISSN 1441e8142. http://virtual-explorer.com.au/ article/2009/224/lithosphere-structure-seismicity. (b) Modified after Brandmayr, E., Marson, I., Romanelli, F., Panza, G. F., 2011. Lithosphere density model in Italy: No hint for slab pull. Terra. Nova 23 292e299.

Chapter 4 Lithosphere structural model of the Campania Plain

Tyrrhenian LVZ as induced by the presence of carbonate-rich melts. Absolute VS tomography correlated with geological and geophysical data of the TRANSMED Project (Carminati et al., 2004) indicates a shallow upper-mantle source for the Apennines-Tyrrhenian igneous system and the absence of a plume beneath Italy and the back-arc basin (Panza et al., 2007b). The conversion of the absolute VS cellular models (Panza et al., 2007a; Panza and Raykova, 2008) into temperature profile (geotherm) for each cell has been performed by Tumanian et al. (2012), considering the effect of compositional variations and of anelasticity for the melt and water presence in the mantle rocks. The thermal model of the upper mantle along a geotraverse crossing Campania (CS2 in Fig. 4.3) shows the following features (Fig. 4.7). A flat cool zone, approximately 100 km thick, is observed at about 50 km of depth beneath the eastern Campania area until the western border of Apulia (cell A7). Based on the density model of Brandmayr et al. (2011), the flat cold lithosphere beneath cells A5eA6 could be interpreted like the remnant of the subducted Adriatic plate, a promontory of the African continent, which did not sink into the upper mantle because of its relatively low density. The downward deflection of the 1400
C isotherm beneath cell A4 could be considered the persisting thermal effect of the Adria plate subduction or as an effect of the subducted Ionian plate. The melt distribution is only roughly related to temperatures: about 2% melt is present beneath Ischia (cell A3), whereas the 1% melt isoline is present at about 100 km of depth and rises to about 50 km going eastward.

Figure 4.7 Temperature and melt fraction (isolines) distribution along a W-E section (CS2 in Fig. 4.3) from Northern Sardinia to Southern Apulia. Modified after Tumanian, M., Luce Frezzotti, M., Peccerillo, A., Brandmayr E., Panza, G. F., 2012. Thermal structure of the shallow upper mantle beneath Italy and neighbouring areas: correlation with magmatic activity and geodynamic significance. Earth Sci. Rev. 114 369e385.

67

68

Chapter 4 Lithosphere structural model of the Campania Plain

Temperatures above 1600
C are obtained at the bottom of the section (300 km). These relatively high values are in agreement with Anderson (2011), who suggests that the upper mantle may be above its solidus and that the surface manifestations (such as heat flow, volcanism, degassing) of the mantle features are the effect of lithospheric structures and stress regimes rather than the mantle peculiarities.

Crustal structure of the Campania Plain The shallower crust of the Campania Plain is the result of the geodynamic context responsible for the dislocation of the Meso-Cenozoic units piled up during the Apenninic orogenesis. Such sedimentary units, outcropping at the massifs bordering the Plain, mainly consist of basins and carbonate platforms deposited from Triassic to Upper Cretaceous age and later covered by terrigenous Miocene sediments. The subsidence, very active in the Quaternary age and driven by NW-SE and NE-SW subvertical faults, has been compensated by a high sedimentation rate (at least 800 m/MA) (Ippolito et al., 1973). Therefore, the Campania Plain has been filled in by marine, transition, and continental deposits interbedded by volcanic deposits deriving from the volcanic districts set on the structural lineaments (Roccamonfina, Campi Flegrei, and Mt. Vesuvius), which controlled the magma rise from deep to shallow reservoirs (Milia and Torrente, 2011). The top of the carbonate sequence was not reached by deep drillings (Fig. 4.2). On the other hand, ambiguity in identification pertains to trachytic lavas and carbonates given their density and seismic velocities likeness (Nunziata and Rapolla, 1981). A seismic reflecting horizon with VP velocity of 4e6 km/s (VS of 2.2e3.3 km/s by assuming a VP/VS ratio of 1.8) was detected in the Gulfs of Naples and Pozzuoli and interpreted as the carbonate horizon (Finetti and Morelli, 1974). On land, such horizon was detected by local gravimetric and seismic surveys at depths of 2e4 km (e.g., Carrara et al., 1973; Berrino et al., 1998; Nunziata and Costanzo, 2010; and references therein). At Ischia, the trachytic basement, retrieved at about 1 km of depth in the center of the island, is characterized by VS in the range 2.2e2.4 km/s (Strollo et al., 2015). The thickness of the Meso-Cenozoic sedimentary sequence is a still open question. Two models have been hypothesized, so far, for the Southern Apennine thrust-belt evolution: 1. a thinskinned model, that is, the sedimentary thrust sheets were

Chapter 4 Lithosphere structural model of the Campania Plain

detached from the lower plate basement, marked by the presence of a magnetic contrast, which remained essentially undeformed and 2. a thick-skinned model, which considers the involvement of the basement, strongly deformed, and forming a large wedge in the accretionary prism (e.g., Menardi Noguera and Rea, 2000 and references therein). Mostardini and Merlini (1986), based on a semiquantitative interpretation of aeromagnetic surveys, estimated a total thickness of 11e12 km and favored model 1. Improta and Corciulo (2006), through the nonlinear inversion of refraction and wide-angle reflection seismic data in the SannioIrpinia region, in the east of the Campania Plain area, estimated a thickness of 8e9 km and favored model 2. The crystalline basement, with VP> 7 km/s, was detected at the bottom of the sedimentary sequence.

VS models of the Campania Plain VS models in the crust and upper mantle of the Campania Plain and surroundings have been defined through the nonlinear inversion of the average group velocity dispersion curves of Rayleigh wave fundamental mode extracted from ambient noise cross-correlations (NC) and earthquake recordings (Fig. 4.8) (Nunziata, 2010; Nunziata and Costanzo, 2010; Nunziata and Gerecitano, 2012; Costanzo and Nunziata, 2014, 2017). Group velocities have been sampled up to a period of 7 s and have been combined, in the inversion, with the dispersion data (phase and group velocity) of the relevant cells A4 and a4 (Panza et al., 2007a) (Fig. 4.9). The nonlinear inversion has been performed with the Hedgehog method (for details, see Panza et al., 2007a and references therein), consisting of an optimized Monte Carlo search of velocityedepth distributions. For paths crossing two cells, the inversion has been performed using the pertinent regional data separately. The thickness of the inverted structural model is 73 km for cell A4 and 41 km for cell a4. A thick-skinned structural model for the Southern Apennine thrust-belt evolution in the central part of the Campania Plain is consistent with the VS models (Costanzo and Nunziata, 2014). A good correspondence exists with the geological sequences along the SW-NE Sections (8 and 9) after Mostardini and Merlini (1986), up to 8e9 km of depth (Fig. 4.10). The thickness of the Apennine carbonate sequence along Section 9 is well in agreement with the total thickness of the layers with VS increasing from 2.3e2.4 km/s to 2.85e3.15 km/s. Moreover, along Section 8, the ambiguity between volcanic and sedimentary rocks is evident as the VS of 2.3e2.4 km/s can be attributed both to volcanic products (site

69

70

Chapter 4 Lithosphere structural model of the Campania Plain

Figure 4.8 Map of the Campania region and surroundings with location of seismic stations (triangles) and noise cross-correlation (NC) and earthquake (star) paths (dashed lines) below which VS models have been computed. The pertinent portions of the 1
 1
cells of the Italic lithosphereeasthenosphere system to the study area are also shown (Panza et al., 2007a; Brandmayr et al., 2010). CF, Campi Flegrei.

2) and to continental and marine sediments (site 3). Instead, the VS value of w3.85 km/s, detected at 8e9 km of depth, cannot be attributed to the Lower Lagonegro basin sequence where, considering the VP velocities by Improta et al. (2003) and assuming a VP/VS ratio of 1.8, the VS values should be in the range 2.4e3.4 km/s. The VS value of 3.85 km/s can be attributed to the metamorphic rocks of the magnetic basement lying at w12 km in the geological sections. A N-S cross section (A-G) from Roccamonfina to the Gulf of Naples has been composed using pertinent models (Fig. 4.11). The VS models obtained below Roccamonfina (Nunziata and Gerecitano, 2012) have been assigned to A. The models in B and C are from the Campania Plain (Costanzo and Nunziata, 2014), while the others are representative of the Campi Flegrei district (Costanzo and Nunziata, 2017). Moreover, the VS model in B is representative both of the Sessa-Naples path, sampled

Chapter 4 Lithosphere structural model of the Campania Plain

71

Figure 4.9 Top: Average Rayleigh wave dispersion data with error bars of the paths sampling maximum periods Tmax  4 s. Bottom: Data used in the inversion are local group velocity data (Costanzo and Nunziata, 2014, 2017) combined with the relevant regional, group, and phase velocity data (Panza et al., 2007a).

with earthquake recordings, and the CV-CE path, sampled with NC measurements (Costanzo and Nunziata, 2014). The Campania structure is characterized by an alluvial and/or pyroclastic cover (VS w0.7 km/s), 0.2 km thick, overlying a thick sequence of tuffs and tuffites interbedded with trachytic lava layers (VS increasing from w1.2 to w1.7 km/s). In the gulf of Pozzuoli, incoherent soils are present up to w0.8 km of depth with VS lower than 1 km/s. South of Roccamonfina, VS increases to 2.2e2.5 km/s at about 2.0e2.5 km of depth and to 2.8e3.3 km/s at 3e4 km of depth, but at Roccamonfina, it is

72 Chapter 4 Lithosphere structural model of the Campania Plain

Figure 4.10 VS models obtained below noise cross-correlation (NC) paths (1, 2, 3 numbers) at the crossing points with the geological sections 8 and 9 after Mostardini and Merlini (1986). Modified after Costanzo, M.R., Nunziata, C., 2014. Lithospheric VS models in the Campanian Plain (Italy) by integrating Rayleigh wave dispersion data from noise cross-correlation functions and earthquake recordings. Phys. Earth Planet. Inter 234 46e9. https://doi. org/10.1016/j.pepi.2014.05.002.

Chapter 4 Lithosphere structural model of the Campania Plain

73

Figure 4.11 VS models and their interpretation along the AeG cross section (located in the top). The variability of the inverted VS and percentage of velocity reduction are also reported.

shallower than 2 km. If we assume a VP/VS ratio of 1.8, the VS values 2.2e3.3 km/s fall in the VP range 4.0e6.4 km/s measured in the Campanian carbonate sequence (Finetti and Morelli, 1974; Improta et al., 2003), with the lowest value representative of highly fractured rocks. Anyway, the presence of trachytic lava cannot be excluded due to the observed density and similarity of seismic

74

Chapter 4 Lithosphere structural model of the Campania Plain

velocities of the carbonate sequence and trachytic lava (Costanzo and Nunziata, 2014 and references therein). A sharp increment of VS (3.7e3.9 km/s) is detected about 5 km below Roccamonfina and at w7e8 km of depth from the Campania plain up to the Gulf of Naples. It can be realistically attributed to the presence of metamorphic rocks or, at Roccamonfina, following Nunziata and Gerecitano (2012), to a solidified magma body. A key feature is the VS decrement of 5%e10% detected above the Moho discontinuity lying at 22e26 km of depth. This low VS layer has been found, with different percentage of velocity reduction, in the Campania region by taking into account all investigated paths (Fig. 4.12). The top of such low-velocity layer rises from depths of 14e15 km, in the Campania Plain, to 11e12 km below the Campi Flegrei district, and to about 6 km of depth toward Mt. Vesuvius, with a higher percentage of velocity reduction (15%). This is in agreement with the wide and extended magma sills, about 1 km thick with VS w1 km/s, which have been inferred at about 8 km beneath Campi Flegrei (Zollo et al., 2008) and Mt. Vesuvius (e.g., Auger et al., 2001) from active seismic experiments.

Figure 4.12 Isobaths (km) of the top of the VS reduction and percentage of reduction.

Chapter 4 Lithosphere structural model of the Campania Plain

Conclusions The lithospheric structure of the Campania Plain has been defined by multiscale seismic surface wave absolute tomographic studies in Italy and neighboring areas. The joint interpretation of seismic studies and the independent geological, geophysical, and petrological information confirms the existence of the westward subducting Apenninic lithosphere, which is almost vertically bent by the mantle easterly directed flow. The subduction process seems to be driven by mantle flow rather than by slab pull (Brandmayr et al., 2011; Doglioni and Panza, 2015). A soft mantle with VS w4.20 km/s is found at about 25 km of depth and reaches about 73 km of depth. It overlies two faster layers (VS w4.4 km/s), which extend down to about 300 km of depth. The upper crust is about 9 km thick and overlies a lower crust of metamorphic rocks (VS w3.8 km/s). The average thickness of the carbonate horizon is about 6 km, even if the presence of lava bodies cannot be excluded as well, given the similarity of densities and seismic velocities of the two kinds of rocks. A key feature is the low VS layer, which rises from depths of 14e15 km, in the Campania Plain, to 11e12 km below the Campi Flegrei district, and to about 6 km of depth toward Mt. Vesuvius, where the percentage of velocity reduction is as large as about 15%. The widespread presence of a low-velocity crustal layer fairly agrees with independent geochemical evidences that are supportive of the presence of an extended magmatic source responsible of ignimbritic events (De Vivo et al., 2010). The presence of the high percentage of velocity reduction below the Campi Flegrei District and Mt. Vesuvius down to the Moho discontinuity seems to be consistent with the presence of a reservoir fed from a deep source in the upper mantle, from which the pockets of magma may rise to shallower depths for a residence time that is still a matter of debate.

References Anderson, D.L., 2011. Hawaii, boundary layers and ambient mantle e geophysical con-straints. J. Petrol. 52 (7e8), 1547e1577. Auger, M., Gasparini, P., Virieux, J., Zollo, A., 2001. Seismic evidence of an extended magmatic sill under Mt. Vesuvius. Science 294, 1510e1512. Berrino, G., Corrado, G., Riccardi, U., 1998. Sea gravity data in the Gulf of Naples: a contribution to delineating the structural pattern of the Vesuvian area. J. Volcanol. Geotherm. Res. 82, 139e150. Boyadzhiev, G., Brandmayr, E., Pinat, T., Panza, G.F., 2008. Optimization for non-linear inverse problems. Rend. Lincei 19, 17e43.

75

76

Chapter 4 Lithosphere structural model of the Campania Plain

Brandmayr, E., Raykova, R.B., Zuri, M., Romanelli, F., Doglioni, C., Panza, G.F., 2010. The lithosphere in Italy: structure and seismicity. In: Beltrando, M., Peccerillo, A., Mattei, M., Conticelli, S., Doglioni, C. (Eds.), The Geology of Italy, Journal of the Virtual Explorer, Electronic edn, p. 36 paper 1 ISSN 1441-8142. http://virtual-explorer.com.au/article/2009/224/lithospherestructure-seismicity. Brandmayr, E., Marson, I., Romanelli, F., Panza, G.F., 2011. Lithosphere density model in Italy: No hint for slab pull. Terra. Nova 23, 292e299. Brandmayr, E., 2012. The Geodynamics of the Mediterranean in the Framework of the Global Asymmetric Earth: Evidences from Seismological and Geophysical Methods. PhD thesis. University of Trieste. Carminati, E., Doglioni, C., Scrocca, D., 2004. Alps vs Apennines. Special Volume of the Italian Geological Society for IGC 32 Florence. Carrara, E., Iacobucci, F., Pinna, E., Rapolla, A., 1973. Gravity and magnetic survey of the Campanian volcanic area, southern Italy. Boll. Geofis. Teor. Appl. 15, 39e51. Costanzo, M.R., Nunziata, C., 2014. Lithospheric VS models in the Campanian Plain (Italy) by integrating Rayleigh wave dispersion data from noise crosscorrelation functions and earthquake recordings. Phys. Earth Planet. Inter 234, 46e59. https://doi.org/10.1016/j.pepi.2014.05.002. Costanzo, M.R., Nunziata, C., 2017. Inferences on the lithospheric structure of the Campi Flegrei District (southern Italy) from seismic noise crosscorrelation. Phys. Earth Planet. Inter 265, 92e95. De Vivo, B., Rolandi, G., Gans, P.B., Calvert, A., Bohrson, W.A., Spera, F.J., Belkin, H.E., 2001. New constraints on the pyroclastic eruptive history of the Campanian volcanic Plain (Italy). Miner. Petrol. 73, 47e65. De Vivo, B., Petrosino, P., Lima, A., Rolandi, G., Belkin, H.E., 2010. Research progress in volcanology in the Neapolitan area, southern Italy: a review and some alternative views. Miner. Petrol. 9, 1e28. Doglioni, C., Gueguen, E., Harabaglia, P., Mongelli, F., 1999. On the origin of west-directed subduction zones and application to the western th, S. (Eds.), The Mediterranean Basins: Mediterranean. In: Durand, J., Horva Tertiary Extension within the Alpine Orogen, vol. 156. Geological Society of London, pp. 541e561. Doglioni, C., Panza, G.F., 2015. Polarized plate tectonics. Adv. Geophys. 56, 1e167. Du, Z.J., Michelini, A., Panza, G.F., 1998. EurID: a regionalized 3D seismological model of Europe. Phys. Earth Planet. Inter 105, 31e62. Finetti, I., Morelli, C., 1974. Esplorazione sismica a riflessione nei golfi di Napoli e Pozzuoli. Boll. Geofis. Teor. Appl. 16, 175e222. Frezzotti, M.L., Peccerillo, A., Panza, G.F., 2009. Carbonate metasomatism and CO2 lithosphereeasthenosphere degassing beneath the Western Mediterranean: an integrated model arising from petrological and geophysical data. Chem. Geol. 262, 108e120. Gueguen, E., Doglioni, C., Fernandez, M., 1997. Lithospheric boudinage in the Western Mediterranean back-arc basin. Terra. Nova 9, 184e187. Improta, L., Bonagura, M., Capuano, P., Iannacone, G., 2003. An integrated geophysical investigation of the upper crust in the epicentral area of the 1980, MS¼6.9, Irpinia earthquake (southern Italy). Tectonophysics 361, 139e169. Improta, L., Corciulo, M., 2006. Controlled source non-linear tomography: a powerful tool to constrain tectonic models of the southern Apennines orogenic wedge, Italy. Geology 34, 41e944.

Chapter 4 Lithosphere structural model of the Campania Plain

Ippolito, F., Ortolani, F., Russo, M., 1973. Struttura marginale tirrenica dell’ Appennino Campano: reinterpretazioni dei dati di antiche ricerche di idrocarburi. Mem. Soc. Geol. Ital. 12, 227e250. Levshin, A.L., Yanovskaya, T.B., Lander, A.V., Bukchin, B.G., Barmin, M.P., Ratnikova, L.I., Its, E.N., 1989. In: Keilis-Borok, V.I. (Ed.), Seismic Surface Waves in a Laterally Inhomogeneous Earth. Kluwer, Norwell, Mass. Menardi Noguera, A., Rea, G., 2000. Deep structure of the campanianeLucanian arc (southern Apennine, Italy). Tectonophysics 324 (4), 239e265. Milia, A., Torrente, M.M., 2011. The possible role of extensional faults in localizing magmatic activity: a crustal model for the Campanian Volcanic Zone (eastern Tyrrhenian Sea, Italy). J. Geol. Soc. 168 (2), 471e484. Mostardini, F., Merlini, S., 1986. Appennino centro-meridionale. Sezioni geologiche e proposta di modello strutturale. Mem. Soc. Geol. Ital. 35, 177e202. Nunziata, C., Rapolla, A., 1981. Interpretation of gravity and magnetic data in the Phlegraean fields geothermal area, Naples, Italy. J. Volcanol. Geotherm. Res. 9, 209e225. Nunziata, C., 2010. Low shear-velocity zone in the Neapolitan-area crust between the Campi Flegrei and Vesuvio volcanic areas. Terra. Nova 22, 208e217. Nunziata, C., Costanzo, M.R., 2010. Low VS crustal zones in the campanian plain (southern Italy). Miner. Petrol. 100, 215e225. Nunziata, C., Gerecitano, F., 2012. VS crustal models of the Roccamonfina volcano and relationship with Neapolitan volcanoes (southern Italy). Int. J. Earth Sci. 101 (5), 1371e1383. Orecchio, B., Presti, D., Totaro, C., Neri, G., 2014. What earthquakes say concerning residual subduction and STEP dynamics in the Calabrian Arc region, south Italy. Geophys. J. Int. 199, 1929e1942. Panza, G.F., 1976. Phase velocity determination of fundamental Love and Rayleigh waves. Pure Appl. Geophys. 114, 753e764. Panza, G.F., Peccerillo, A., Aoudia, A., Farina, B., 2007a. Geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings: the Tyrrhenian Sea and surroundings. Earth Sci. Rev. 80, 1e46. Panza, G.F., Raykova, R.B., Carminati, E., Doglioni, C., 2007b. Upper mantle flow in the western Mediterranean. Earth Planet. Sci. Lett 257, 200e214. Panza, G.F., Raykova, R.B., 2008. Structure and rheology of lithosphere in Italy and surrounding. Terra. Nova 20, 194e199. Peccerillo, A., 2003. Plio-Quaternary magmatism in Italy. Episodes 26, 222e226. Peccerillo, A., 2017. Cenozoic Volcanism in the Tyrrhenian Sea Region, second ed. Springer International Publishing AG, p. 399. Peccerillo, A., 2019. Campania Volcanoes: Petrology, Geochemistry and Geodynamic Implications (this book). Peccerillo, A., Panza, G.F., 1999. Upper mantle domains beneath CentralSouthern Italy: petrological, geochemical and geophysical constraints. Pure Appl. Geophys. 156, 421e443. Rolandi, G., Bellucci, F., Heizler, M.T., Belkin, H.E., De Vivo, B., 2003. Tectonic controls on the genesis of ignimbrites from the campanian volcanic zone, southern Italy. Mineral. Petrol. 79, 3e31. Stracke, A., Hofmann, A.W., Hart, S.R., 2005. FOZO, HIMU, and the rest of the mantle zoo. Geochem. Geophys. Geosyst. 6, Q05007. https://doi.org/10.1029/ 2004GC000824.

77

78

Chapter 4 Lithosphere structural model of the Campania Plain

Strollo, R., Nunziata, C., Iannotta, A., Iannotta, D., 2015. The uppermost crust structure of Ischia (southern Italy) from ambient noise Rayleigh waves. J. Volcanol. Geotherm. Res. 297, 39e51. Tumanian, M., Luce Frezzotti, M., Peccerillo, A., Brandmayr, E., Panza, G.F., 2012. Thermal structure of the shallow upper mantle beneath Italy and neighbouring areas: correlation with magmatic activity and geodynamic significance. Earth Sci. Rev. 114, 369e385. Van Keken, P.E., 2003. The structure and dynamics of the mantle wedge. Earth Planet. Sci. Lett. 215, 323e338. Vitale, S., Ciarcia, S., 2018. Tectono-stratigraphic setting of the Campania region (southern Italy). J. Maps 14 (2), 9e21. Yanovskaya, T.B., 2001. In: Keilis-Borok, V.I., Molchan, G.M. (Eds.), Development of Methods for Surface-Wave Tomography Based on Backus-Gilbert Approach, vol. 32. Computational Seismology, pp. 11e26. Zollo, A., Maercklin, N., Vassallo, M., Dello Iacono, D., Virieux, J., Gasparini, P., 2008. Seismic reflections reveal a massive melt layer feeding Campi Flegrei caldera. Geophys. Res. Lett. 35, L12306.

5 Campania volcanoes: petrology, geochemistry, and geodynamic significance Angelo Peccerillo Retired from Department of Earth Sciences, University of Perugia, Perugia, Italy

Introduction The Campania Volcanic Province (Fig. 5.1) consists of the active centers of SommaeVesuvio, Campi Flegrei (Phlegraean Fields) and Ischia, in addition to the islands of Procida and Vivara. The volcanoes are sited between the Southern Apennines and the Tyrrhenian Sea basin, in a tectonically subsided area cut by NW-SE and E-W trending faults and filled with thick piles of sediments (e.g., Milia and Torrente, 2003, 2015; Fowler, 2019, this book and references therein). Measured ages of volcanism range from about 0.2 Ma to 1944 AD, when the last eruption of Vesuvio took place. Older PlioPleistocene volcanism is buried beneath the Campanian Plain, covered by the thick successions of the Campi Flegrei volcano. Because of their location in an intensely populated area and the violently explosive nature of eruptions, the Campania volcanoes have attracted the attention of scholars since ancient times. An enormous amount of data has been collected in the last decades. Yet, several volcanological, petrological, and geodynamic aspects of the volcanism remain controversial. In this chapter, the main petrological and geochemical characteristics of the Campania volcanic centers are summarized, and the hypotheses on magma genesis and evolution are discussed. The geodynamic significance, in the ambit of the Italian Quaternary volcanism, will be finally addressed.

Vesuvius, Campi Flegrei, and Campanian Volcanism. https://doi.org/10.1016/B978-0-12-816454-9.00005-5 Copyright © 2020 Elsevier Inc. All rights reserved.

79

80

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Figure 5.1 Location of the Campania volcanic centers with simplified distribution of volcanic products. Relief shaded map is from Tarquini et al. (2012).

Structural setting of volcanism in the Italian peninsula The Campania magmatism is a part of a long Plio-Quaternary volcanic belt running from Southern Tuscany to the Aeolian Islands. Rock compositions show all orogenic-type trace element signatures such as high ratios of large-ion lithophile elements (LILE) versus high field strength elements (HFSE) (i.e., La/Ta, Th/Ta, Rb/Nb, etc.) and moderately to strongly radiogenic Sr isotope ratios. However, there are many along-belt compositional variations that allow distinguishing several distinct magmatic provinces (e.g., Peccerillo, 2002, 2017). Such a subdivision is not a merely speculative petrological exercise but reveals distinct petrogenetic processes for magmatism along the Italian peninsula, with profound implications for geophysics and geodynamics (Peccerillo, 2017 and references therein). The distribution of magmatic provinces is reported on a structural model of the Apennines and back-arc regions (Fig. 5.2), simplified after Pierantoni et al. (2019, this book). It is obvious that each magmatic province, as defined by magmatological characteristics, occupies a distinct structural segment behind the Apennine chain. This is a clear evidence for the close relationships between magmatism and geodynamics along the Italian peninsula. The main orogenic volcanic provinces include 1. Tuscany Province, consisting of a Miocene to Pleistocene association of a very wide variety of rock types, including

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Figure 5.2 Structural framework of the Italian peninsula and position of magmatic provinces. Simplified after Pierantoni et al. (2019, this book).

2.

3.

4.

5.

6.

peraluminous crustal anatectic granites and rhyolites, calcalkaline and shoshonitic suites, and lamproites. Intra-Apennine Province, containing a few 0.8e0.4 Ma old lava and pyroclastic deposits showing ultrapotassic kamafugitic compositions. Some carbonate-rich pyroclastics have been interpreted as carbonatites. Roman Province, made up of huge amounts of potassic and ultrapotassic rocks erupted in the last 0.8 Ma by large stratovolcanoes and volcanic complexes with polygenetic calderas (Vulsini, Vico, Sabatini, Colli Albani). The Roman Province defined here is much more restricted than the original one recognized by Washington (1906), which also included Ernici, Roccamonfina, and Campania volcanoes. Ernici-Roccamonfina Province, made up by comparatively low volumes of about 0.6e0.1 Ma-old products that show a very wide range of compositions, from calcalkaline and shoshonitic to ultrapotassic. The calcalkaline to potassic volcanics show geochemical affinities with the Campania Province. Pontine Islands Province, consisting of several centers with trachybasaltic to rhyolitic compositions and ages ranging from 4.2e0.13 Ma. Campania Province, formed by the dormant volcanoes of SommaeVesuvio, Campi Flegrei, and Ischia and by the island of Procida and the nearby islet of Vivara. Rock compositions

81

82

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

range from trachybasalt to trachyte and phonolite. Leucite tephrite to leucite phonolite are restricted to SommaeVesuvio. 7. Apulian or Lucanian Province, formed by the isolated volcano of Monte Vulture (w0.8e0.1 Ma) that erupted various types of undersaturated rocks (melilitites, tephrites, foidites, etc.) rich in both Na2O and K2O, in addition to late carbonatite lavas and pyroclastics. Vulture magmas are petrologically distinct from Campania volcanics, although there is an overlap of radiogenic isotope compositions. 8. Aeolian arc Province, consisting of seven major islands, some islets, and a number of seamounts. Volcanological, geochemical, and petrological evidence highlights the occurrence of three distinct sectors: western, central, and eastern. Surprisingly, the easternmost island of Stromboli shows closer geochemical affinities with the Campania volcanoes than with other nearby Aeolian centers. There are other Quaternary volcanic provinces in Sicily, Sardinia, and in the Tyrrhenian Sea. These mostly have Ocean Island Basalts (OIB)e to Mid-Ocean Ridge Basalts (MORB)etype anorogenic geochemical characteristics whose role in the origin of Campania magmatism will be recalled during the following sections.

A volcanological overview of the Campania Province The Campanian volcanoes show variable volcanological characteristics. Activity has been prevailingly explosive, but lavas are abundant at SommaeVesuvio (e.g., Santacroce, 1987). The erupted mafic products show moderately potassic alkaline affinity and degree of silica undersaturation. However, strongly undersaturated ultrapotassic- and leucite-bearing rocks are abundant at SommaeVesuvio (Fig. 5.3). SommaeVesuvio is a stratovolcano consisting of an older cone (Somma) with a polygenetic caldera where the Vesuvio cone has been built up during the last 2000 years. Volcanic sequences overlay a suite of about 2 km thick sedimentary and volcanoclastic material, sitting over 6e8 km thick Mesozoic carbonates that are commonly found as lithic ejecta, often intensively affected by metamorphism and metasomatism (e.g., Fulignati et al., 2000 and references therein). Hercynian crystalline basement occurs at depth, over a Moho at about 30 km (e.g., Berrino et al., 1998; Tondi and De Franco, 2003; De Natale et al., 2006).

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

83

Figure 5.3 (A) Total alkali versus silica (TAS; Le Maitre, 2002) classification diagram of SommaeVesuvio rocks; the dashed line is the boundary between the alkaline and subalkaline fields of Irvine and Baragar (1971). Data normalized to 100% on an LOI-free basis; (B) DQ versus K2O/Na2O diagram. DQ is the algebraic sum of normative quartz minus undersaturated minerals leucite, nepheline, kalsilite, and olivine; rocks with DQ < 0 and DQ > 0 are undersaturated and oversaturated in silica, respectively (Peccerillo, 2017). The shaded area is the field of mafic rocks (MgO > 4.0 wt%). Samples with LOI higher than 4% have been excluded because of possible secondary modifications. Data from Joron et al. (1987), Ayuso et al. (1998), Rolandi et al. (1998), Somma et al. (2001), Paone (2006, 2008), Piochi et al. (2006), Di Renzo et al. (2007), Aulinas et al. (2008), Sulpizio et al. (2010).

The Somma activity started about 33 ka BP. with prevailing emission of lava flows and scoriae, presently cropping out along the caldera walls and at a few parasitic centers (Santacroce, 1987; Macdonald et al., 2015). Starting from around 18.3 ka (Pomici di Base eruption), volcanism become more explosive, with Plinian eruptions and several phases of caldera collapses separated by mildly explosive interplinian stages (e.g., Rolandi et al., 1998; Somma et al., 2001). Vesuvio started to grow after the 79 AD eruption and has been active until 1944, giving several explosive and lava eruptions interrupted by periods of dormancy. Borehole drilling on the southern flank of Vesuvio found lavas and pyroclastic that yielded 40Ar/39Ar ages of about 0.4 Ma, the oldest products in the Campania Province (Brocchini et al., 2001). Campi Flegrei is a large volcanic complex with two calderas and several intracaldera centers. Volcanism has been mostly explosive, from phreatomagmatic to Plinian. Oldest ages (40Ar/39Ar) of 205 and 157 ka have been measured at Taurano, east of Naples, in an area outside the calderas (De Vivo et al., 2001). Younger activity includes the Campanian Ignimbrite (w39e40 ka; e.g., Gebauer et al., 2014; Rolandi et al., 2019, this book and references therein) and the so-called Neapolitan Yellow Tuff (w15 ka; e.g., Deino et al., 2004). The following volcanism gave a number of hydrovolcanic explosions with formation of tuff rings, tuff cones, and a

84

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

few maar volcanoes. The last eruption in 1538 AD built up Monte Nuovo, a pyroclastic cone near the town of Pozzuoli (Piochi et al., 2005). Campi Flegrei is well known for its slow vertical ground movements (bradeysism) continuing from at least Roman times to present day (Cannatelli et al., 2019, this book). The volcano feeding system consists of a 3e4 km deep trachytic reservoir, periodically refilled by about 8 km deep mafic magma chamber (e.g., Zollo et al., 2008; De Siena et al., 2010; D’Antonio, 2011). The shallow reservoir is probably hosted in siltite, sandstone, and shale sediments; the deeper chamber is within the Hercynian crystalline basement (e.g., Pappalardo et al., 2002; Piochi et al., 2014). Carbonate series such as those of the SommaeVesuvio area seem to be absent beneath Campi Flegrei (D’Antonio, 2011). The exposed Phlegraean volcanism was preceded by about 2 Ma-old volcanism found by borehole drilling in the Campanian Plain. Rocks are typically mafic-intermediate calcalkaline in composition, indicating that subalkaline magmatism preceded alkaline activity in the Campanian Plain (Barbieri et al., 1979). Ischia is the remnant of a large volcano shaped by a prevailingly explosive activity, volcanotectonic collapses, gravitational sliding, and erosion. Its volcanic history and the stratigraphic succession are complex. The lowest exposed rocks are older than 150 ka; a main phase of activity occurred at about 55 ka with the emplacement of the Monte Epomeo Green Tuff ignimbrite and the formation of a caldera; younger activity took place between 16 ka to Middle Ages. The latest eruption emplaced maficintermediate lavas and scoriae in the Arso area, eastern Ischia, in 1302 AD (Gillot et al., 1982). The Islands of Procida and the nearby islet of Vivara are sited between Campi Flegrei and Ischia. They have been constructed by both phreatomagmatic and magmatic explosive activity, from about 70 to 15 ka (e.g., D’Antonio and Di Girolamo, 1994; De Astis et al., 2004; Fedele et al., 2006). The two islands are made of trachybasalt to trachyte pyroclastic rocks. However, calcalkaline basalts are found among lithic clasts, suggesting that subalkaline magmatism preceded the potassic alkaline activity that built up the two islands.

Petrology and geochemistry of the Campania volcanoes Petrological and geochemical characteristics of Campania volcanics show strong differences among the various volcanoes and

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

within single centers. A summary of compositions is reported in Table 5.1. Most of the variability is an effect of shallow level evolutionary processes, but it also records heterogeneities of the mantle sources. Discriminating between the two factors is difficult, but it is crucial for placing constraints on the compositions of parental melts and upper mantle, and for understanding geodynamic setting.

SommaeVesuvio The SommaeVesuvio rocks range from trachybasalt to phonotephrite, tephriphonolites, trachyte, and phonolite (Fig. 5.3A). Mafic rocks (here defined as those with MgO >4.0 wt%) range from slightly to strongly undersaturated in silica (Fig. 5.3B), the latter containing leucite as a main phenocryst and groundmass phase. Based on major and trace element variations, three main suites of rocks have been recognized at SommaeVesuvio by Joron et al. (1987). Such a partition is followed in this chapter, with a few modifications of time limits between the series, which have no effects on petrological discussion. One rock series consists of moderately silica-undersaturated trachybasalts, shoshonites, latites, trachytes, and trachyphonolites. These were prevailingly erupted before about 9 ka (Fig. 5.3) and will be here referred to as the Older Series. A second series consists of prevailing undersaturated tephriphonolites and phonolites, which were mainly emplaced between the Older Series and the early historical times; this will be referred to as Prehistorical Series. Finally, a third suite of rocks consists of strongly undersaturated phonotephrite to phonolite, erupted from 79 AD to the present (Younger Series). All the rocks have variably porphyritic textures; olivine phenocrysts occur in the mafic rocks of the Older and Younger Series. Clinopyroxene is ubiquitous; plagioclase is particularly abundant in the Older Series. Leucite is a common phase of the Younger Series, whereas it is present in the trachybasalts of the Older Series and the intermediate rocks of the Prehistorical Series. K-feldspar is restricted to evolved rocks; FeeTi oxides, apatite, garnet, and amphibole are common accessories in the felsic rocks. Nepheline appears in the most evolved rocks of the Prehistorical and Younger Series (Joron et al., 1987). Evolution processes of SommaeVesuvio and other Campania magmas are complex, as discussed by Fowler (2019, this book). However, first-order information can be provided by some key interelement variation diagrams (e.g., Ayuso et al., 1998;

85

Table 5.1 Major trace element and radiogenic isotope compositions of selected Campania volcanics. Sample

1

2

3

Volcano

Sommae Vesuvio Older series

Sommae Vesuvio Older series

Sommae Vesuvio Older series

Locality/ eruption SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Sc V Cr Co Ni Rb Sr Y Zr Nb Cs

K-trachybasalt scoria 48.10 1.08 16.10 8.10 0.12 4.20 9.18 3.96 2.34 0.74 2.82 18 55 26 34 390 750 40 265 43 14.2

4

Sommae Vesuvio Prehistorical series Phonotephrite Trachyphonolite Phonotephrite lava pumice pumice 49.50 57.70 50.90 1.01 0.39 0.70 18.09 17.80 18.40 8.20 3.77 6.42 0.14 0.15 0.14 3.95 0.55 2.79 7.67 3.30 7.66 2.48 3.46 3.39 6.61 7.78 6.57 0.79 0.13 0.39 0.32 3.97 1.49 3 11 231 47 51 28 3 17 34 3 11 247 315 350 1322 715 890 32 40 33 319 355 270 52 46 36 14.0 18.9 21.7

5

6

7

9

10

11

12

13

Sommae Vesuvio Younger series Phonotephrite scoria 47.50 0.96 16.10 8.17 0.15 5.16 9.88 2.37 6.90 0.83 0.35

Sommae Vesuvio Younger series Foidite pumice 49.10 0.50 20.80 4.59 0.14 1.10 5.90 5.28 9.05 0.21 1.74 3

Campi Campi Flegrei Flegrei

8

Ischia

Ischia

10

10

14

Trachybasalt scoria 48.25 1.27 16.20 8.55 0.14 8.58 12.04 2.84 1.78 0.34 0.10

Trachyte pumice 59.56 0.45 19.20 3.86 0.17 0.62 2.61 4.62 8.78 0.12 2.00

20 9 1500 25 290 92 15.2

Latute scoria 53.98 1.13 18.13 6.95 0.14 3.76 7.28 4.67 3.47 0.49 0.71 17 163 46 22 32 183 638 30 183 28 8.3

Trachyte lava 62.21 0.57 18.46 3.41 0.31 0.45 1.10 7.27 6.18 0.04 1.94 3 32

107 29 17 268 1050 28 233 32 14.0

Latite lava 53.35 0.84 17.87 1.90 0.13 2.56 6.18 5.22 3.34 0.58 1.53 11 206 8 15 5 315 919 31 240 30 12.7

202 338 40 125 57 532 22 114 13 2.2

34 e 1 292 341 35 371 61 18.2

Basaltic lithic 48.35 1.24 15.48 7.88 0.14 9.54 12.01 2.85 1.47 0.28 0.77 37 207 421 42 150 46 492 21 102 12

Trachyte pumice 59.88 0.45 18.21 4.38 0.12 0.62 2.73 4.13 9.27 0.21 3.96 3 65

361 409 38 318 38

2 542 20 68 1041 147 27.2

Ba La Ce Nd Sm Eu Gd Tb Yb Lu Hf Ta Pb Th U 87 Sr/86Sr 143 Nd/144Nd 206 Pb/204Pb 207 Pb/204Pb 208 Pb/204Pb Source of data

1220 52 90 45.7 10.8 2.20 1.10 2.20 0.30 5.90 2.80 22 20.9 4.7 0.70711 0.51250 19.049 15.652 39.149 Ayuso et al. (1998)

2522 84 167 71.9 13.3 3.30 9.70 1.34 2.50 0.36 6.90 3.30 38 25.2 6.8 0.70687 0.51255 19.095 15.741 39.356 Di Renzo et al. (2007)

1050 68 124 45.8 9.6 1.97

1450 68 119 44.9 9.1 2.01

2360 51 99 47.9 9.7 2.50 7.52 1.08 1.96 0.26

1950 101 162 48.7 7.6 1.70

1651 58 114 51.3 10.1 2.60 8.00 1.03 0.87 0.70 1.10 3.02 2.18 1.80 2.40 0.42 0.30 0.20 0.40 7.23 5.40 5.00 2.89 2.07 1.50 4.00 1.90 44 53 30 84 29.6 28.5 27.4 19.9 42.2 20.5 8.1 8.3 6.8 14.7 6.0 0.70765 0.70752 0.70685 0.70700 0.70772 0.51243 0.51247 0.51245 0.51249 0.51257 18.956 18.955 18.977 19.024 19.016 15.636 15.639 15.647 15.646 15.68 38.981 38.98 39.005 39.22 39.126 Piochi et al. Somma et al. Somma et al. Paone DAntonio (2006), (2001) (2001) (2006) et al. Paone (2006) (1999)

345 81 153 54.5 10.2 2.20 8.20

1135 53 95 48.4 9.1 2.20 7.90 1.02 2.80 2.56 0.40 0.38 4.31 1.50 60 12 30.0 14.7 3.9 0.70751 0.70636 0.51255 0.51254 18.926 18.993 15.682 15.69 38.953 39.134 Orsi et al. Casalini (1995), et al. DAntonio (2017, et al. 2018) (2007)

10 161 295 119.2 18.5 1.04 16.92 2.33 10.54 1.66 25.99 9.16 60 93.3 10.4 0.70775 0.51255 19.222 15.708 39.355

561 18 38 22.0 5.1 1.64 0.75 1.86 0.30 2.75 0.89 7.9 3.4 0.9 0.70524 0.51269 19.088 15.678 39.153 De Astis et al. (2004)

78 86 165 63.0 10.9 2.33

521 14 32 18.3 4.4 1.47 4.58 1.21 0.72 3.38 1.83 0.51 0.27 8.12 2.70 3.90 0.86 47.9 13.45 32.2 2.9 10.7 1.0 0.70678 0.70514 0.51254 0.51272 19.24 18.675 15.699 15.637 39.342 38.682 De Astis Mazzeo et al. et al. (2004) (2014)

88

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Mastrolorenzo et al., 2006; Paone, 2006; Piochi et al., 2006; Santacroce et al., 2008; Sulpizio et al., 2010). Na2O shows a moderate increase with decreasing MgO (Fig. 5.4A) in the mafic-intermediate composition to rise sharply in the trachytephonolite rocks; several samples, mostly from the Prehistorical Avellino eruption, plot along linear (mixing) trends, mostly extending form intermediate to felsic compositions (dashed lines). TiO2 (and FeOtotal, not shown) remains rather constant at high-intermediate values of MgO but decreases sharply in the evolved samples. Again linear trends between intermediate and felsic compositions are defined by the Avellino eruption and a few other samples (Fig. 5.4B). Al2O3 shows somewhat scattered negative trend with MgO for most samples, except for the intermediate-felsic rocks of the Older Series that plot along a flat trend (Fig. 5.4C).

Figure 5.4 Variation diagrams of selected major and trace elements for SommaeVesuvio rocks. Dashed lines indicate possible mixing trends. Solid lines with arrows are fractionation crystallization trends. Source of data as for Fig. 5.3.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

89

Trace elements furnish additional details. Sr increases with decreasing MgO for the Younger Series and for some samples of the Older Series, whereas it remains constant in the mafic range to decrease in the felsic compositions for the other rocks (Fig. 5.4D). The samples of the Prehistorical Series again plot along two distinct trends, both connecting intermediate and felsic composition, one being linear (mixing) and the other curvilinear (fractional crystallisation). Similar, through more scattered, distribution is shown by Ba (not shown). Sr versus Th diagram shows an overall positive trend for the Younger Series and for the mafic rocks of the Older Series (Fig. 5.5A). Negative trends with different slopes are observed in the Prehistorical Series and in the intermediate-felsic samples of the Older Series. Ba has a similar behavior, though with more scattering for the Younger Series (Fig. 5.5B). Distinct curvilinear and liner trends are particularly well observed on some compatible

Figure 5.5 Interelement variations diagrams for SommaeVesuvio. Dashed lines are mixing trends. Solid lines with arrows are fractionation crystallization trends of different mineral assemblages. Source of data as for Fig. 5.3.

90

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

versus compatible element diagrams, such as V versus Ni (Fig. 5.5C). Compatible versus incompatible element plots (e.g., Ni vs. Zr) show negative trends for all the three series with sharp increase in the incompatible elements for the most evolved samples of the Prehistorical Series (Fig. 5.5D). SreNd isotopic ratios are rather variable 143 (87Sr/86Sr ¼ 0.7062e0.7078; Nd/144Nd ¼ 0.51225e0.51257). There is no clear correlation with MgO, CaO, or SiO2, except for a very weak positive correlation between Nd isotope ratios and MgO in the Older Series (not shown). Pb isotope ratios are poorly 206 207 variable with Pb/204Pb w18.90e19.10, Pb/204Pb 208 207 w15.55e15.75, and Pb/ Pb w38.80e39.40. There are no systematic differences of radiogenic isotope compositions from one series to the other (Fig. 5.6). Overall, SreNdePb isotope ratios of SommaeVesuvio partially overlap the compositional field of Stromboli volcano (eastern Aeolian arc). Relationships with other magmatic provinces in Italy will be further addressed in the discussion section. Oxygen isotope ratios are rather high both in the whole rocks and separated phases. Ayuso et al. (1998) found whole rock d18O& ¼ 7.3e10.2 relative to SMOW, with a positive trend with CaO wt%. Dallai et al. (2011) find d18OSMOW ¼ 5.5e7.1& in olivine and 6.0e7.5& in clinopyroxenes. Distribution of major and trace elements suggests complex evolution processes for SommaeVesuvio with an interplay of fractional crystallization, wall rock assimilation, and mixing. However, the fractionating mineral assemblages changed from

Figure 5.6 SreNdePb isotope variations in the Campania Province. Fields of other volcanic provinces are from Peccerillo (2017) and references therein. Source of data as for Figs. 5.3, 5.8, 5.10.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

one series to the other and with the degree of evolution of single series (e.g., Joron et al., 1987; Ayuso et al., 1998; Piochi et al., 2006; Santacroce et al., 2008; Pappalardo and Mastrolorenzo, 2010; Fowler, 2019, this book; Stabile and Carroll, 2019, this book). Fractional crystallization of mafic phases, especially clinopyroxene, dominated magma evolution for all the series, joined by feldspars and accessory phases (Ti-magnetite, apatite, garnet) especially in the intermediate-felsic compositions (see solid lines in Figs. 5.4 and 5.5). Clinopyroxene-dominated fractionation generated positive trends of SreBa versus Th and other incompatible elements in the Younger Series and some samples of the Older Series; in contrast, heavy alkali feldspar and plagioclase fractionation are responsible for decrease in SreBa with evolution (increasing Th and decreasing MgO) in the other rocks. Some leucite could have fractionated in the magmas of the Prehistorical and Younger Series. However, this mineral has partition coefficients higher than one only for Rb and Cs (Francalanci et al., 1987) and cannot be responsible for BaeSr decrease in the felsic rocks. Assimilation involved different types of magmas and wall rocks. Assimilation of carbonate rocks in the Younger Series has been demonstrated by oxygen isotope variation in the phenocrysts from Vesuvio (Dallai et al., 2011). Note that carbonate assimilation favors clinopyroxene crystallization (e.g., Iacono Marziano et al., 2008), which favored the continuous increase in Sr and Ba through the Younger Series. Assimilation of silicic rocks may be responsible for SreNd isotope variation in the Older Series (e.g., Pappalardo et al., 2002). Finally, some linear trends observed in the interelement variation diagrams clearly point to magma mixing. Such a process operated in all the magma series, but it is particularly evident for the Prehistorical Avellino rocks (Ayuso et al., 1998; Paone, 2006; Sulpizio et al., 2010). Complexities of magma evolution reveal modification of the magma plumbing system through time. The feeding system of SommaeVesuvio volcano is believed to consist of several magma chambers sited at different depths beneath the surface (De Vivo et al., 2010; Pappalardo and Mastrolorenzo, 2010; Nunziata et al., 2019, this book). It is likely, therefore, that various reservoirs were active at different stages of volcano evolution, giving distinct suites of magmas. Limestones and dolostones host one of the shallow reservoirs, as demonstrated by the large amounts of skarn xenoliths found in the SommaeVesuvio products (e.g., Fulignati et al., 2000 and references therein). Evolution within such a reservoir

91

92

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

had paramount petrological consequences, in particular for the degrees of silica undersaturation, which are unique in the Campania Province. Pichavant et al. (2014) provided experimental evidence supporting an origin of all the SommaeVesuvio magmas from a single type of parent magma (see Stabile and Carroll, 2019, this book). Accordingly, the various suites would be related to different amounts and types of wall rock assimilation, in addition to separation of distinct mineral assemblages. In particular, heavy carbonate assimilation by the Younger Series along with heavy clinopyroxene fractionation generated strong silica undersaturated compositions. In contrast, the other magmas, especially those of the Older Series, evolved by fractional crystallization of clinopyroxene and feldspars and assimilation of wall rocks with siliceous compositions. As a consequence, they did not attain strongly undersaturated compositions, though starting from the same parental magma as the Younger Series. The hypothesis of a single parental magma and variable fractionation paths is strongly supported by geochemical data that basically overlap in the mafic range and define different trends only in the evolved compositions. The complex evolution history of SommaeVesuvio makes it difficult recognizing primary mantle equilibrated composition, which is crucial for understanding the nature of the sources. Incompatible element patterns normalized to primordial mantle (Sun and McDonough, 1989) for mafic rocks (MgO > 3.5 wt%) are very similar to each other, except for modest differences of absolute element abundances (Fig. 5.7A). Moreover, radiogenic isotope signatures do not change strongly with evolution. These data seem to suggest that incompatible element ratios and radiogenic isotope signatures of mafic rocks were not heavily affected by fractional crystallization and assimilation and might be considered as representative of their sources.

Campi Flegrei (Phlegraean Fields) The Campi Flegrei rocks range in composition from shoshonite and latite to dominant trachytes and phonolites, sometimes peralkaline (Fig. 5.8A). Latites and shoshonites are restricted to the younger activity, after the eruption of the Neapolitan Yellow Tuff at 15 ka (e.g., Armienti et al., 1983; Rosi and Sbrana, 1987; Melluso et al., 2012). Most rocks are slightly undersaturated in silica and have moderate potassic alkaline affinity (Fig. 5.8B). Shoshonites and latites contain clinopyroxene, plagioclase, rare olivine, and biotite phenocrysts, set in a groundmass made of abundant sanidine, FeeTi oxides, and glass. Trachytes and

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Figure 5.7 Mantle normalized incompatible element patterns for mafic rocks from the Campania Province. Symbols of SommaeVesuvio as in Figs. 5.3e5.6. Juvenile (asterisks) and lithic lasts (crosses) are distinguished for Procida volcano. Normalizing values and Ocean Island Basalt (OIB, stars) are from Sun and McDonough (1989). Depleted and Enriched Mid-Ocean Ridge Basalts (D-MORB and E-MORB, crosses in panel A and C) are from Gale et al. (2013). Source of data as in Figs. 5.3, 5.8, 5.10.

phonolites have phenocrysts of alkali feldspar, minor clinopyroxene, biotite, plagioclase, and rare amphibole, nepheline, and sodalite-group minerals. Accessory phases include FeeTi oxides, apatite, britholite, zircon, spinel, and titanite (Armienti et al., 1983; Rosi and Sbrana, 1987; Pappalardo et al., 2002; Melluso et al., 2012). Leucite has been rarely observed (Astroni products, Tonarini et al., 2009). Variations of major and trace elements show a decrease in CaO with decreasing MgO, whereas FeOtotal, TiO2, P2O5 V, Sr, and Ba remain constant in the shoshonite-latite field to decrease sharply in the most evolved rocks (Fig. 5.9). Alkalies, Rb, Th, Zr, Y, and rare-earth elements (REE) increase sharply from mafic to evolved

93

94

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Figure 5.8 (A) Total alkali versus silica (TAS) classification diagram of Campi Flegrei rocks; (B) DQ versus K2O/Na2O diagram. For explanation of the diagrams, see caption of Fig. 5.3. The shaded area is the field of mafic rocks (MgO > 3.5 wt%). CI, Campanian Ignimbrite; NYT, Neapolitan Yellow Tuff. Data from Orsi et al. (1995), Civetta et al. (1997), DAntonio et al. (1999), Pappalardo et al. (1999, 2002), Fedele et al. (2008); Pabst et al. (2008), Tonarini et al. (2009), Di Renzo et al. (2011), Piochi et al. (2014), and references therein.

rocks, reaching very high enrichments in the trachyte-phonolite field. The highest concentrations of incompatible element have been found in the Averno 2 and the Monte Nuovo phonolites (Pappalardo et al., 2002). Some samples of the younger activity plot along linear trends between mafic and felsic compositions. Incompatible element patterns normalized to mantle compositions (Sun and McDonough, 1989) of the most mafic samples (MgO > 3.5 wt%) have a shape and degree of element enrichment that resemble closely to SommaeVesuvio (Fig. 5.7B). Abundances of several elements overlap average OIB or E-MORB, but LILE, light rare-earth element (LREE), and Pb are enriched relative to these compositions, as typically observed in subduction-related magmas. SreNd isotope ratios (Fig. 5.6) range from 87Sr/86Sr ¼ 0.7067e0.7086 and 143Nd/144Nd ¼ 0.51239e0.51260 (Orsi et al.,1995; D’Antonio et al., 1999; Pappalardo et al., 1999; Pabst et al., 2008; Di Renzo et al., 2011 and references therein). There is a clear trend of 87Sr/86Sr ratios to increase with MgO, mirrored by an opposite tendency for NdePb isotope ratios (Fig. 5.9E and F). Such a trend is particularly evident if samples younger than 15 ka are considered separately. However, younger activity does not show significant time-related variations of isotopic signatures. Yet, Pappalardo et al. (2002) demonstrate that there is an overall increase of Sr isotope ratios from older to younger activity at Campi Flegrei. Such a time-related isotopic trend is better

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

95

Figure 5.9 Variation diagrams of selected major and trace elements and of SrePb isotope ratios against MgO for the Campi Flegrei rocks. Dashed lines indicate possible mixing trends. Source of data as in Fig. 5.8.

highlighted by the few available uranogenic Pb isotope ratios, which decrease significantly from rocks older than 35 ka and the Campanian Ignimbrite (39 ka) to the Neapolitan Yellow Tuff (15 ka) and the younger activity (Fig. 5.9F). Major and trace element variation diagrams suggest that fractional crystallization of clinopyroxene and feldspars was a

96

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

leading process during magma evolution at Campi Flegrei (e.g., Pappalardo et al., 1999, 2002; Fowler, 2019, this book and references therein). Study of melt inclusions indicates polybaric crystallization from 200 MPa (7.5 km) to 30 MPa (w1 km) (Esposito et al., 2018). Clinopyroxene was the dominant separating phase in the shoshoniteelatite compositions, whereas alkali feldspar fractionated in the trachyte-phonolite magmas. Scattering of element distribution, linear trends observed in some diagrams, and radiogenic isotope variability testify to a role for additional processes, such as magma mixing and assimilation of crustal rocks (e.g., Pappalardo et al., 2002; Di Renzo et al., 2011). Radiogenic isotope behavior, especially 87Sr/86Sr in the rocks younger than 15 ka, is intriguing. Positive trends of 87Sr/86Sr versus MgO are the opposite than normally observed for assimilation processes. They imply higher amounts of crustal contamination in mafic than in felsic magmas. Such a process has been recognized elsewhere (e.g., at Alicudi, Aeolian arc; Peccerillo et al., 2004) and has been explained as an effect of the capability of hot and fluid mafic melts to incorporate and dissolve higher amounts of crustal rocks than the cooler and more viscous felsic magmas. However, isotopic variation might also testify arrival of new type of magmas within the volcano plumbing system. Pappalardo et al. (2002) highlight time-related geochemical variations through the entire Campi Flegrei activity and suggest evolution within two magma reservoirs, respectively hosted by the Hercynian lower crust and by the shallow arenaceous sedimentary cover. Early erupted magmas were less contaminated by crustal material than the younger ones because of the shorter time spent inside the deep reservoir. However, the emplacement during latest activity stages of a compositionally distinct type of primary magma with higher Sr- and lower NdePb isotope signatures than older products cannot be excluded. Recognizing primary compositions at Campi Flegrei is even more difficult than at SommaeVesuvio. Rocks with high MgO are lacking and the most primitive samples probably suffered heavy crustal contamination, as it has been discussed above. Yet, incompatible element patterns of the most mafic rocks are strikingly similar to those from SommaeVesuvio (Fig. 5.7), suggesting similar compositions for primary melts. The derivation of Campi Flegrei and SommaeVesuvio from a single parental magma raises the question about the absence of highly undersaturated leucite-rich rocks in the former. However, if silica undersaturation is the effect of carbonate assimilation, the scarcity of highly undersaturated rocks at Campi Flegrei could

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

be simply explained by a limited or no role for such a process. This conclusion agrees with the model of Pappalardo et al. (2002) who suggest that magma chambers are sited within the Hercynian basement and the siliceous sedimentary substratum and not inside carbonate sequences as at SommaeVesuvio.

Ischia Ischia consists of dominant trachytes, minor phonolites, and latites and rare shoshonites (Fig. 5.10). Basaltic rocks are absent; felsic rocks are sometimes peralkaline (Poli et al., 1987; Crisci et al., 1989; Civetta et al., 1991; Brown et al., 2008, 2014; Melluso et al., 2014; Iovine et al., 2017; Casalini et al., 2018). Rock mineralogy is made up of variable relative amounts of alkali feldspar, plagioclase, clinopyroxene, biotite, and FeeTi oxides phenocrysts; olivine occurs in the shoshonites. Sodalite-group minerals are observed in some trachytes and phonolites. Apatite and titanite are common accessories; aenigmatite, amphibole, aegirine, and ZreCaeNaeREEeF silicates have been found in the groundmass of peralkaline trachyphonolites (Melluso et al., 2014). Variation of selected major and trace elements (Fig. 5.11) show considerable scattering in the felsic compositions and smooth trends in the shoshonite-latite field. Mantle normalized incompatible element patterns are fractionated with negative spikes of

Figure 5.10 (A) Total alkali versus silica (TAS) classification diagram of Ischia and ProcidaeVivara rocks; compositions of basaltic lithics from Procida are also plotted; (B) DQ versus K2O/Na2O diagram. The shaded area is the field of mafic rocks (MgO > 3.0 wt%). For additional explanation on the diagrams, see caption of Fig. 5.3. Ischia data are from Poli et al. (1987), Crisci et al. (1989), Civetta et al. (1991), Brown et al. (2008, 2014), Melluso et al. (2014), Iovine et al. (2017), Casalini et al. (2017, 2018). ProcidaeVivara data are from DAntonio and Di Girolamo (1994), De Astis et al. (2004), Mazzeo et al. (2014), and references therein.

97

98

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Figure 5.11 Variation diagrams of Ischia and ProcidaeVivara rocks. Juvenile and lithic lasts at Procida are indicated with asterisks and crosses, respectively. Source of data as in Fig. 5.10.

HFSE and positive anomalies of Pb and LILE (Fig. 5.7C). Overall, they resemble Campi Flegrei and SommaeVesuvio patterns, although abundances of some LILE are slightly lower, in spite of more evolved compositions at Ischia.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

99

Radiogenic isotope data are variable (Fig. 5.6; 87Sr/86Sr ¼ 0.70538e0.70703; 143Nd/144Nd ¼ 0.51264e0.51249; 176Hf/177Hf ¼ 0.28283e0.28293; 206Pb/204Pb ¼ 18.94e19.23; 207Pb/204Pb ¼ 15.65 e15.71; 208Pb/204Pb ¼ 39.05e39.37) suggesting interaction between magmas and wall rocks and/or occurrence of different types of primary melts (e.g., D’Antonio et al., 2013; Casalini et al., 2018). There is a variation of radiogenic isotopes with time, a relationship that is particularly significant for Pb isotopes (Fig. 5.12). Oxygen isotope compositions on olivine and clinopyroxene phenocrysts range from d18OSMOW ¼ 5.5e6.5&, indicating little interaction with crustal rocks (D’Antonio et al., 2013). Ischia rocks mostly represent evolved compositions. These were likely derived from mafic parents with moderately potassic alkaline affinity. Magma evolution was dominated by fractional crystallization, with separation of mafic minerals joined by plagioclase and alkali feldspars in the intermediate and felsic compositions. Fractional crystallization was accompanied by mixing among compositionally different but comagmatic melts (Melluso et al., 2014). Interaction with the crust was moderate as indicated by oxygen and radiogenic isotope ratios in most of the rocks (D’Antonio et al., 2013; Casalini et al., 2018). Moretti et al. (2013) envisage that major fractionation events occurred in a magma chamber sited at about 8e10 km depth. There is also geochemical and isotopic evidence for fluid enrichments in the

Figure 5.12 Variation diagram of 206Pb/204Pb versus age (in 1000 years, ka) for Ischia volcanics. Crosses are the Monte Epomeo pyroclastic rocks. The stars with arrows point to 206Pb/204Pb ratios (not the age) of the Tyrrhenian Mid-Ocean Ridge Basalt (MORB) (206Pb/204Pb w18.60) and Etna Ocean Island Basalts (OIB) (206Pb/204Pb w19.70e20.10). For data of Etna and Tyrrhenian MORB see Peccerillo (2017) and references therein. Ischia data are from Casalini et al. (2017, 2018) and references therein.

100

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

most evolved rocks and for repeated episodes of magma mixing (e.g., Poli et al., 1987; Civetta et al., 1991; D’Antonio et al., 2013 and many others). Recognizing the nature of primary melts at Ischia is even harder than at other centers. Rocks are more evolved than at any other Campania volcano, and primitive compositions are, in fact, absent. This is also true for melt inclusions in mafic phases that show maximum MgO contents around 4.0 wt% (Moretti et al., 2013). Casalini et al. (2018) show, however, that there is no significant relationship between SreNdeHfePb isotope signatures and the degree of evolution for most rocks, concluding that the observed isotopic variation reflect heterogeneities of mantle sources. These authors also seem to suggest that the parental magmas of Ischia might be represented by the most primitive rocks from Procida, which would imply crustal assimilation in the transition from Procida to Ischia magmas. Mantle-normalized incompatible element patterns of the least evolved rocks are strikingly similar to those of Vesuvio and Campi Flegrei, except for a slightly lower abundance of several incompatible elements (Fig. 5.7C). This is an indication that the Ischia magma sources may have similar trace element ratios as the other Campania volcanoes but lower incompatible element abundances.

Procida Procida and the nearby islet of Vivara consist of pyroclastic rocks (scoriae, hyaloclastites, pumices, and lithics) and a small lava dome. Juvenile materials are potassic alkaline and range from trachybasalt to trachyte (Fig. 5.10A). Mafic scoriae contain phenocrysts of diopside, plagioclase, and some olivine; sanidine phenocrysts occur in the trachytes, along with minor green clinopyroxene and andesine plagioclase (Di Girolamo and Stanzione, 1973; D’Antonio and Di Girolamo, 1994; De Astis et al., 2004, 2006; Fedele et al., 2006). Lithic clasts include silica undersaturated basalts with calcalkaline alkali abundances and ratios (Fig. 5.10B), which are not observed among the juvenile materials. These clasts and the samples from the buried volcanoes beneath Campi Flegrei are the only calcalkaline rocks in the Campania area. Calcalkaline basaltic clasts are porphyritic with phenocrysts of Mg-rich olivine and diopside, set in a matrix containing plagioclase, Ti-magnetite, rare alkali feldspar, and glass. Some olivine crystals contain inclusions of MgeCr-spinel.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

The ProcidaeVivara juvenile clasts show decreasing TiO2, MgO, FeO, ferromagnesian trace elements, and Sr and increase for alkalies and incompatible elements with increasing silica (Fig. 5.11). There is some scattering for several elements, especially among mafic rocks. Incompatible element patterns of the most primitive samples are fractionated and have a shape that resembles closely shoshonites from Ischia (Fig. 5.7C and D). However, absolute element enrichment is lower at ProcidaeVivara also because of more primitive compositions. SreNd isotope ratios show the most primitive compositions among Campania volcanics (87Sr/86Sr ¼ 0.7052e0.70733; 143 144 Nd/ Nd ¼ 0.5125e0.5127), whereas Pb isotopes overlap Ischia values (Fig. 5.6). He isotope ratios of olivine show R/RA ¼ 4.76e5.21, significantly higher than at other Campania volcanoes (R/RA ¼ 2.5e3.5) and partially overlapping rocks from Stromboli (R/RA ¼ 2.7e4.8) (Martelli et al., 2004, 2008). Basaltic lithics show high MgO, Ni, and Cr, which nearly fall in the compositional range of mantle-equilibrated melts. These samples also have the lowest incompatible element abundances and Sr isotope ratios in the Campania Province. 206Pb/204Pb ratios show relatively unradiogenic compositions and are shifted toward the Tyrrhenian MORB and the EM1-type (Enriched Mantle 1) basalts erupted by the Plio-Quaternary volcanoes in Sardinia (e.g., Gasperini et al., 2000, 2002; Lustrino et al., 2000). Geochemical variation suggests that fractional crystallization was a main evolutionary process at ProcidaeVivara. Radiogenic isotope variability also requires interaction with the crust (D’Antonio et al., 1999). There is an overlap of elemental variation trends of ProcidaeVivara and Ischia, which supports the Procida magmas as parental to Ischia (Casalini et al., 2018 and references therein). Procida hosts the only primitive rocks occurring in Campania. High MgO concentrations are also found among melt inclusions in olivine phenocrysts of juvenile clasts (Esposito et al., 2011, 2018 and references therein), suggesting a direct feeding from the upper mantle for these centers. Compared with other Campania volcanoes, ProcidaeVivara juvenile mafic rocks have similar patterns of incompatible elements but lower elemental abundances (Fig. 5.7). The lithic clasts have much less enriched compositions as well as lower LILE/HFSE ratios than juvenile equivalents. Therefore, two types of primary magmas can be recognized at ProcidaeVivara. The occurrence of two types of basaltic composition has also been

101

102

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

demonstrated among olivine-hosted melt inclusions from Procida juvenile clasts (Esposito et al., 2011, 2018).

Petrogenesis of Campania magmas The Campania volcanoes are built up by a wide variety of rock types, ranging from mafic to felsic and from slightly oversaturated to strongly undersaturated in silica. Petrological and geochemical evidence suggests the occurrence of a single type of parental magma with a broadly trachybasaltic composition for all the centers. However, complex evolution processes generated the wide ranges of compositions observed among the erupted products.

Large regional magma chambers beneath Campania The complexity of evolution processes of trachybasaltic parental magmas at regional scale is best summarized by variations of radiogenic isotopes against any evolution parameter. A plot of 87 Sr/86Sr versus MgO is reported in Fig. 5.13A. It is obvious that the data, although much scattered, roughly fall in a triangularshaped area whose base is occupied by mafic magmas. In other words, mafic rocks show a larger range of compositions than felsic

Figure 5.13 (A) Variation diagram of 87Sr/86Sr versus MgO for the Campania Province. Arrows indicate possible evolution (mixing) trends of mafic magmas. Samples with Sr lower than 10 ppm have not been plotted to avoid compositions that are too readily modifiable by negligible assimilation or alteration; (B) La versus 87Sr/86Sr variation of mafic rocks. Samples with MgO >3.0 wt% have been plotted with the aim of including a significant number of samples from all volcanoes. Source of data as in Figs. 5.3, 5.8, 5.10.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

ones, but all converge toward a common, though wide, field defined by trachyte-phonolites. Such an array highlights the occurrence of isotopically different types of both mafic and felsic magmas, with the former showing larger variation. Moreover, convergence toward the trachytic-phonolitic field suggests an interaction of mafic melts with felsic magmas at the regional scale, implying the occurrence of a large phonolitic-trachytic reservoir (or a system of reservoirs), with which mafic melts coming from the source or from deeper reservoirs interacted (mixed) before being erupted at the surface. Seismic tomography suggests that a partially melted sill occurs beneath the active volcanoes of Campania at a depth between 7 and 14 km (e.g., Zollo et al., 2008; Fowler, 2019, this book and references therein). Moreover, Nunziata et al. (2019, this book) find a level with low S-wave velocity that starts from a depth of about 14e15 km and reaches the Moho. Such a layer extends continuously from the Roccamonfina volcano in the north to Vesuvio and Gulf of Naples, occupying the intermediate lower crust beneath the entire Campania Province. These authors conclude that geophysical data are consistent with the occurrence of a large regional magma reservoir (or a system of adjoining reservoirs) fed by mantle-derive melts. Therefore, a two-layer regional magma ponding system is suggested by geophysical evidence. Such a conclusion fits particularly well geochemical data. It is beyond the objective of this chapter discussing the complex issue of the plumbing system of Campania volcanoes (see Fowler, 2019, this book; Stabile and Carroll, 2019, this book). However, the model that best explains isotopic data is that of an upper reservoir (or various adjoining reservoirs) filled with trachyte-phonolite magmas derived from trachybasalt parents by dominant fractional crystallization and showing a more restricted range of isotopic compositions than mafic magmas ponding in a deeper reservoir(s). Different batches of mafic magmas ascending from depth cross and mix with evolved magmas sitting in the upper reservoir(s), modifying their isotopic signatures toward the trachyte-phonolite compositions. Large range of isotopic ratios of mafic melts may reflect stronger crustal assimilation in the deep magma chambers. However, this does not explain low Sr isotopic ratios of mafic magmas at Procida, suggesting that source heterogeneity must be assumed for Campania magmas.

103

104

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Compositions of primary melts The effects of evolutionary processes on the compositions of mafic rocks cannot be considered as fully understood. Therefore, compositions of primary melts are still rather speculative. However, it has been amply demonstrated that much of the trace element and isotopic variation of mafic rocks cannot be simply accounted for by evolutionary processes and likely reflects mantle source heterogeneity (e.g., Iovine et al., 2018 and references therein). Incompatible element patterns of mafic rocks support this conclusion. In spite of the complex evolutionary history described above, they show remarkable similar shapes for the different centers (Fig. 5.7), suggesting these represent pristine features. There is only a variation of incompatible trace element abundances, which decrease from SommaeVesuvio and Campi Flegrei to Ischia and ProcidaeVivara, in parallel with variations of SreNd isotope ratios (Fig. 5.13B). Therefore, geochemical evidence suggests heterogeneous mantle sources showing variable degrees of enrichments but similar distribution patterns of incompatible elements. Such a compositional array can be obtained by variable degrees of metasomatism by a single type of fluid or melt, which modified, with more intensity, the mantle source at Campi Flegrei and SommaeVesuvio than at the western centers of Ischia and Procida. Alternatively, one may hypothesize that a homogeneously metasomatized source underwent late mixing with a depleted source such as the Tyrrhenian MORB-type mantle, a process that was more significant in the western sector of the magmatic province.

Nature of mantle sources and metasomatism Fractionated incompatible element patterns with positive spikes of LILE, especially Pb, and negative anomalies of HFSE for the Campania Province are obvious arc signatures and strongly support an origin in a mantle that had been modified by subduction-related processes (Di Girolamo, 1978; Serri, 1990; De Astis et al., 2000; Peccerillo, 1999, 2001 and many others). SreNdePb isotope ratios of mafic rocks show that Campania volcanoes plot on a continuous trend between mantle and upper crust compositions, along with all the other orogenic volcanics from CentraleSouthern Italy (Fig. 5.14). Such an array clearly demonstrates an interaction between mantle and crustal components (Hawkesworth and Vollmer, 1979; Peccerillo, 2017

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

105

Figure 5.14 (A) SreNd isotope diagram for mafic rocks (MgO > 3%) from Campania. Curved lines are mixing trends between Ocean Island Basalts (OIB)etype mantle and upper crustal rocks (marls and siliceous rocks). Note that the magmatic provinces plot along distinct mixing curves, suggesting variable roles of siliceous and marly sediments in source contamination; (B) 87Sr/86Sr versus 206Pb/204Pb diagram. Large arrows indicate trends of Procida mafic clasts and Pontine Islands (Ventotene) toward Sardinia EM1-type compositions. Compositions of mantle endmembers FOZO (Focus Zone), DMM (Depleted MORB Mantle) and Enriched Mantle 1 (EM1), and Tyrrhenian Mid-Ocean Ridge Basalt MORB (star) are also reported. Compositional fields of other magmatic province in the Tyrrhenian Sea area are reported for comparison (Peccerillo, 2017 and references therein). Source of data as in Figs. 5.3, 5.8, 5.10.

and references therein). Various amounts of siliceous and carbonate sediments are believed to be involved in the mantle metasomatism (e.g., Peccerillo, 1999; Mazzeo et al., 2014; Iovine et al., 2018). Premetasomatic mantle endmembers may have had FOZO-type (Focus Zone) OIB or MORB-type compositions (e.g., Serri, 1990; Morris et al., 1993; Ayuso et al., 1998; Casalini et al., 2018; Iovine et al., 2018). Both compositions are widespread in the Mediterranean area and are well represented by the Etna FOZOeOIB and by the Tyrrhenian Sea MORB (e.g., Lustrino and Wilson, 2007). The Campania Province plots in the middle of the trend between Etna and the upper crust, indicating moderate contamination of an FOZOeOIB source by sediments. Similar isotopic compositions as Campania are shown by the Stromboli volcano (Fig. 5.6) and to a much minor extent by Vulture, pointing to a common origin for all these magmas (De Astis et al., 2000; Peccerillo, 2001). Interaction between sediments and mantle components is also supported by low He isotope ratios, high B, and low d11B of Central Italy and Campania volcanics (e.g., Martelli et al., 2004, 2008; Tonarini et al., 2004, 2009). Geochemical modeling carried out by various authors (e.g., D’Antonio et al., 2007, 2013; Mazzeo et al., 2014; Iovine et al., 2018) suggests that subduction-related fluids released from an

106

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

oceanic-type slab and associated sediments are able to explain the geochemical and isotopic signatures of Campania volcanoes. Sediment contribution ranges from 2% to 10%. Regional variations of incompatible trace element and radiogenic isotope ratios suggest that the sediment signature is stronger at SommaeVesuvio and Campi Flegrei than at Procida and Ischia. Such a variation could be attributed to the arrival of variable amounts of metasomatic fluids from the slab. However, it cannot be excluded that heterogeneity is a postmetasomatic feature, related to mixing between metasomatized Campania mantle and Tyrrhenian MORB, as recalled earlier in this discussion. Note that Ischia and Procida are sited nearest to the Tyrrhenian back-arc basin and, therefore, are more readily affected by MORB-type mantle from the west. The decrease of Pb isotopic ratios with time at Ischia (Fig. 5.12) may record an increasing role of depleted MORB-type components from earlier to latest activity. Combined LILE and HFSE and radiogenic isotope evidence can shed some further light on these issues. HFSE (Ta, Nb, Zr, Hf, Ti) are known to be relatively immobile during arc metasomatism (e.g., Kessel et al., 2005). Therefore, their abundances and ratios in mafic rocks furnish information on pristine mantle compositions. By contrast, LILE (Cs, Rb, Ba, K, Pb, LREE) are easily transferred by subduction-related fluids. Therefore, they cannot tell much on premetasomatic mantle compositions but give indications on the nature and degree of enrichment processes. HFSE abundances of Campania volcanoes are close to average OIB of Sun and McDonough (1989), whereas other Central Italy volcanoes such as Colli Albani (Alban Hills) have compositions close to E-MORB (Fig. 5.15A). Moreover, HFSE/HFSE ratios (e.g., Nb/Zr) in Campania are midway between OIB-type rocks of Etna and the Tyrrhenian MORB; Stromboli and Vulture basically plot in the same field of Campania, although Vulture is closer to Etna. In contrast, Colli Albani volcano plots with the Tyrrhenian MORB (Fig. 5.15B). Ernici-Roccamonfina falls between Campania and Colli Albani. These data suggest a role for both MORB- and OIB-type mantle pre-metasomatic sources along the Italian peninsula. MORB-type components dominated beneath the Roman Province; instead, OIB-type component contributed significantly to Campania, Vulture, and Stromboli magmatism. Ernici and Roccamonfina represent somewhat mixed compositions between Campania and Roman Provinces (Peccerillo, 2002, 2017). Moreover, LILE abundances and ratios and radiogenic isotope ratios indicate that metasomatism had different nature and much higher intensity for Roman than for Campania volcanoes. In conclusion, the Roman and the Campania volcanoes differ for both pristine

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

107

Figure 5.15 (A) Mantle normalized incompatible element patterns of mafic rocks (MgO > 3.5%) from Campania (shaded area) compared with Colli Albani (Alban Hills) and Stromboli mafic potassic samples; (B) Nb/Zr versus 206 Pb/204Pb diagram for mafic rocks (MgO > 3.0%) from Campania. Ischia samples with MgO >2.0 wt% have been plotted because of the scarcity of mafic compositions. The fields of other volcanic areas are shown for comparison. Source of data as for Fig. 5.14.

mantle compositions and for compositions and degrees of metasomatism, strongly arguing against the commonly held view that Campania is a continuation of the Roman Province. PbeSr isotopic ratios furnish some additional information on a role of another mantle endmember, at least for the older activity (Fig 5.14B). While the Italian volcanics, including the Campania rocks, plot along a mixing trend between Etna (FOZOeOIB) and the upper crust, the basaltic lithics from Procida depart from the main trend pointing toward low 206Pb/204Pb compositions. A similar trend, but at higher Sr isotope values, is observed in the Pontine Island (Ventotene, 0-8e0.1 Ma old), offshore the coast of Campania. Pb isotope data, therefore, support a role for a third component in the origin of some older Campania magmas and for Ventotene. This endmember has lower 206Pb/204Pb than Tyrrhenian MORB, a feature that is only shown by EM1-type Plio-Quaternary volcanics from Sardinia (e.g., Gasperini et al., 2000, 2002; Lustrino et al., 2000). Such a component may have played a role in the older magmatism offshore the Campania Plain but seems absent or negligible in the more recent volcanism. In conclusion, the complex evolution of mantle source beneath Campania could be summarized as follows. An OIB-type premetasomatic mantle was affected by contamination by fluids coming from a subduction zone. Both sediments and a basaltic oceanic-type slab contributed to composition of

108

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

metasomatic fluids. These affected at variable degrees the Campania mantle sources and were stronger beneath SommaeVesuvio and Campi Flegrei than at Procida and Ischia. Alternatively, metasomatism was homogeneous, but geochemical variations at the regional scale were generated by a postmetasomatic interaction of Campania mantle with a depleted mantle source such as that of Tyrrhenian MORB. An EM1 component might have played a role in the older magmatism in Campania and Pontine Islands.

Geodynamic implications The geodynamic significance of the volcanism in Central Italy has been the subject of a longstanding and still active debate. Most authors suggest that the entire volcanism occurring from Southern Tuscany to the Aeolian arc is subduction-related and results from mixing at the regional scale between mantle and upper crust. Two main mantle components, essentially MORB- and OIB-types, and various amounts and types of terrigeneous to marly sediments are believed to participate in the mixing (e.g., Peccerillo, 1999, 2017 with references; Conticelli et al., 2010 and many others). Regional variation of trace element and radiogenic isotope signatures along the peninsula has brought to recognize a number of magmatic provinces (Fig. 5.2). These result from different intensity and composition of the sedimentary contaminant, as well as from distinct premetasomatic mantle sources (Peccerillo, 2017 and references therein). Petrologicalegeochemical variation of magmatism, in turn, speaks for a complex and variable geodynamic setting along the Apennine subduction zone. Although this general picture is widely, though not unanimously, accepted, several aspects remain controversial. The occurrence of strongly undersaturated leucite-rich rocks at SommaeVesuvio has led to consider the Campania volcanoes as a district of the Roman ultrapotassic alkaline magmatic province (e.g., Conticelli et al., 2010; Melluso et al., 2014). However, it has been argued in the previous discussion that the strong degree of silica undersaturation at SommaeVesuvio may not reflect the compositions of primary melts but rather the effect of assimilation of carbonate wall rocks (e.g., Pichavant et al., 2014 and references therein). This hypothesis implies that strongly undersaturated ultrapotassic primary melts as those occurring in the Roman Province are lacking in Campania. Trace element and radiogenic isotope signatures also militate against a close genetic relationship between the Roman and

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Campania provinces and rather demonstrate compositional affinities between Campania and Stromboli and, to a less extent, Mount Vulture (De Astis et al., 2000; Peccerillo, 2002). The close compositional similarity between Campania volcanoes and Stromboli requires a single type of contaminant superimposed over the same type of mantle material. Contamination could be provided by the Ionian plate that is actively subducting beneath the southern Tyrrhenian Sea (e.g., Orecchio et al., 2014 and references therein).

A possible geodynamic scenario The geodynamic scenario that best explains petrologicale geochemical variations of volcanism along the Tyrrhenian border of the Italian peninsula is that while Roman volcanoes are related to subduction of the Adriatic plate and contamination by marly sediments of a MORB-type premetasomatic mantle, a distinct subduction process of the Ionian plate affected an OIB-MORB type source beneath Campania, the eastern Aeolian arc, and Vulture. The Adriatic plate is of continental type, whereas the Ionian plate is believed to be oceanic or thinned continental in nature (Speranza et al., 2012 and references therein). It is obvious, therefore, that the type and amounts of upper crustal material brought into the mantle had strikingly different compositions for the two subduction systems. The limit between the two plates runs in an NW-SE direction south-west of Apulia (e.g., Sani et al., 2016; Pierantoni et al., 2019, this book). The evolution of the Adriatic-Ionian subduction system is discussed by Pierantoni et al. (2019, this book). A continuous plate was initially subducting beneath the Apennine chain. Eastward migration of the subduction system brought to fragmentation of the both the Apennine chain and of the Adriatic-Ionian foreland. The northern Adriatic sector collided earlier and possibly underwent slab break-off. Collision in the southern sector of the Adriatic plate (i.e., Apulia) occurred about 0.8 Ma (Patacca and Scandone, 2001), shortly before the onset of Vulture activity at about 0.75 Ma (Villa and Buettner, 2009). In contrast, the oceanic-type Ionian sector continued sinking into the mantle beneath the southern Tyrrhenian Sea. Collision in the Apulia sector generated an along-strike tearoff of the subducting slab, as suggested by Wortel and Spakman (2000), Spakman and Wortel (2004), and Panza et al. (2007). In other words, there was a slab breakoff in Apulia, whereas in the south, the slab remained attached to the Ionian foreland, continuing its sinking into the upper mantle while retreating

109

110

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

south-eastward (e.g., Gvirtzman and Nur, 1999; Rosenbaum and Lister, 2004; Panza et al., 2007; Peccerillo, 2017 with references). It is suggested that dehydration of the Ionian oceanic slab and associated sediments produced mantle contamination and melting both beneath the eastern Aeolian arc and Campania (Fig. 5.16). Pierantoni et al. (2019, this book) show a somewhat distinct model in which a slab coming from Apulia occurs beneath Campania, whereas the Ionian slab is subducting beneath the Aeolian arc. According to this model, two distinct slab sectors, respectively, coming from Apulia and the Ionian Sea, should be responsible for mantle contamination and magmatism in Campania and the Aeolian arc. Such a hypothesis, however, is at odds with geochemical data, which require the same type of source contamination for Campania and Stromboli, related to the same type of fluids. It is unlikely that compositionally homogeneous fluids were released from two distinct slabs; geochemical data are better explained by a common origin of fluids from a single Ionian-subducting zone, though fluids might originate at different depths along the slab. Slab tear-off along the subduction hinge and rollback can furnish an explanation for the origin of the OIB- and MORBtype mantle components beneath CampaniaeStromboli. OIB-type material could be provided by asthenospheric mantle

Figure 5.16 Schematic model for the evolution of the Ionian Sea subduction system. (A) Subduction of a continuous slab from AdriaeApulia to the Ionian Sea. (B) Apulia collision at about 0.8 Ma and onset of along-strike slab break-off, with opening of a window through which foreland asthenosphere is suctioned onto the subducting slab (red arrow). (C) Present situation with a narrow Benioff zone extending from the eastern Aeolian arc to Campania. Red arrows indicate asthenospheric mantle inflow from the foreland and possible input from the Tyrrhenian Sea area.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

inflow from the foreland onto the subducting Ionian slab. Southeastern slab rollback could have suctioned asthenospheric mantle from the Apulia-Ionian foreland thus involving OIB-type components in the subduction factory (Peccerillo and Frezzotti, 2015 and references therein). Asthenospheric material from the foreland had a similar characteristic as the Etna magma source, which has an almost pure FOZO-type composition. Access to the subduction zone for the asthenosphere from the foreland occurred through the window opened by the along strike slab tear-off of the Apulia-Ionian plate. Rollback may have attracted additional mantle material from the west, i.e., from the Tyrrhenian Sea, thus justifying the MORB-type component at Ischia and Procida. In conclusion, the geochemistry of Campania magmas may result from the contribution of OIB- and MORB-type materials. Both these components are allochthonous and, respectively, come from the foreland and from the Tyrrhenian Sea area. OIB-type asthenospheric mantle migrated from the foreland onto the Ionian subduction zone and was contaminated by fluids delivered by the Ionian slab. A distinct mantle inflow occurred form the west and only affected the westernmost centers of Ischia and Procida. The same type of contamination hypothesized for Campania and Stromboli may also have affected the Vulture source. In the latter case, however, the role of OIB was stronger because of Vulture position close to the Apulia foreland, i.e., to the source of OIB component (De Astis et al., 2000).

Conclusions The main conclusions on the origin, evolution, and geodynamic significance of the Campania Province can be summarized as follows: 1. The Campania volcanoes have a wide range of compositions that were generated by complex evolution processes. These involved fractional crystallization, mixing, and assimilation of different types of wall rocks. Magmas with broadly trachybasaltic compositions were parental to all the volcanic suites in Campania. Evolution followed distinct trends at various volcanoes or also at different stages of single centers because of modification of the chemicophysical conditions of magma chambers and the nature of wall rocks. Heavy carbonate assimilation occurred at SommaeVesuvio, generating strongly undersaturated compositions that are absent at other centers.

111

112

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

2. The Campania volcanoes are petrologically and geochemically distinct for other magmatic provinces in Central Italy. In particular, they differ from the Roman volcanoes by showing lower LILE abundances, lower LILE/HFSE ratios, lower Sr and higher Nd isotope ratios, and much more variable and overall higher Pb isotopic ratios. Moreover, primary ultrapotassic-undersaturated compositions that are common in the Roman Province are absent in the Campania volcanoes, as the leucite-bearing rocks at SommaeVesuvio are related to carbonate assimilation by a trachybasalt parent. By contrast, the Campania volcanoes show close geochemical similarities with Stromboli volcano, indicating similar source compositions and geodynamic setting. 3. The sources of Campania and Stromboli volcanoes consist of a mixture of premetasomatic FOZOeOIB-type mantle similar to Etna and MORB. MORB-type component is more evident beneath the western volcanoes of Ischia and Procida than at Campi Flegrei and SommaeVesuvio. 4. Mantle metasomatism beneath the eastern Aeolian arc and Campania was accomplished by fluids released by the subducting oceanic Ionian slab and associated sediments. The common nature of premetasomatic source and of the contaminating materials generated geochemically similar magmas in Campania and the eastern Aeolian arc, supporting a single slab as a source of metasomatic fluids. 5. The geodynamic model that best explains petrological and geochemical evidence suggests that the OIB-type component of the eastern Aeolian arc and Campania volcanoes was provided by inflow from the IonianeApulian foreland. Mantle probably inflow also occurred from the Tyrrhenian area and mainly affected Ischia and Procida. Inflow from the foreland onto the Ionian subduction zone took place through the along-strike tear-off of the Ionian slab and was favored by suctioning during rollback toward the southeast.

Acknowledgment The data used in this chapter come from many research articles, mostly carried out in the last two decades. Citing all the papers is impossible. A complete list of the data and their sources is reported by Peccerillo (2017) and supplementary material. Constructive comments by Gianfilippo de Astis (INGV) and Michael R. Carroll (University of Camerino) greatly contributed to improve the manuscript.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

References trich, N., Armienti, P., Barberi, F., Bizouard, H., Clocchiatti, R., Innocenti, F., Me Rosi, M., Sbrana, A., 1983. The Phlegraean fields: magma evolution within a shallow chamber. J. Volcanol. Geotherm. Res. 17, 289e311. Aulinas, M., Civetta, L., Di Vito, M.A., Orsi, G., Gimeno, D., FernandezTuriel, J.L., 2008. The Pomici di Mercato Plinian eruption of SommaVesuvius: magma chamber processes and eruption dynamics. Bull. Volcanol. 70, 825e840. Ayuso, R.A., De Vivo, B., Rolandi, G., Seal II, R.R., Paone, A., 1998. Geochemical and isotopic (Nd-Pb-Sr-O) variations bearing on the genesis of volcanic rocks from Vesuvius, Italy. J. Volcanol. Geotherm. Res. 82, 53e78. Barbieri, M., Di Girolamo, P., Locardi, E., Lombardi, G., Stanzione, D., 1979. Petrology of the calc-alkaline volcanics of the Parete-2 well (Campania, Italy). Per. Min. 48, 53e74. Berrino, G., Corrado, G., Riccardi, U., 1998. Sea gravity data in the Gulf of Naples: a contribution to delineating the structural pattern of the Vesuvian area. J. Volcanol. Geotherm. Res. 82, 139e150. Brocchini, D., Principe, C., Castradori, D., Laurenzi, M.A., Gorla, L., 2001. Quaternary evolution of the southern sector of the Campanian Plain and early Somma-Vesuvius activity: insights from the Trecase 1 well. Mineral. Petrol. 73, 67e91. Brown, R.J., Orsi, G., de Vita, S., 2008. New insights into Late Pleistocene explosive volcanic activity and caldera formation on Ischia (Southern Italy). Bull. Volcanol. 70, 583e603. Brown, R.J., Civetta, L., Arienzo, I., D’Antonio, M., Moretti, R., Orsi, G., Tomlinson, E.L., Albert, P.G., Menzies, M.A., 2014. Geochemical and isotopic insights into the assembly, evolution and disruption of a magmatic plumbing system before and after a cataclysmic caldera-collapse eruption at Ischia volcano (Italy). Contrib. Mineral. Petrol. 168, 1035. Cannatelli, C., Bodnar, R.J., De Vivo, B., Lima, A., 2019. Ground movement (bradyseism) in the Campi Flegrei volcanic area: a review. In: De Vivo, B., Belkin, H.E., Rolandi, G. (Eds.), Vesuvius, Campi Flegrei, and Campanian Volcanism. Geology, Petrology, and Related Risk. Elsevier (This book). Casalini, M., Heumann, A., Marchionni, S., Conticelli, S., Avanzinelli, R., Tommasini, S., 2017. Geochemical and radiogenic isotope probes of Ischia volcano, Southern Italy: constraints on magma chamber dynamics and residence time. Am. Mineral. 102, 262e274. Casalini, M., Heumann, A., Marchionni, S., Conticelli, S., Avanzinelli, R., Tommasini, S., 2018. Inverse modelling to unravel the radiogenic isotope signature of mantle sources from evolved magmas: the case study of Ischia volcano. Ital. J. Geosci. 137, 420e432. Civetta, L., Gallo, G., Orsi, G., 1991. Sr- and Nd-isotope and trace-element constraints on the chemical evolution of the magmatic system of Ischia (Italy) in the last 55 ka. J. Volcanol. Geotherm. Res. 46, 213e230. Civetta, L., Orsi, G., Pappalardo, L., Fisher, R.V., Heiken, G., Ort, M., 1997. Geochemical zoning, mingling, eruptive dynamics depositional processes: the Campanian Ignimbrite, Flegrei caldera, Italy. J. Volcanol. Geotherm. Res. 75, 183e219. Conticelli, S., Laurenzi, M.A., Giordano, G., Mattei, M., Avanzinelli, R., Melluso, L., Tommasini, S., Boari, E., Cifelli, F., Perini, G., 2010. Leucitebearing (kamafugitic/leucititic) and -free (lamproitic) ultrapotassic rocks and associated shoshonites from Italy: constraints on petrogenesis and

113

114

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

geodynamics. In: Beltrando, M., Peccerillo, A., Mattei, M., Conticelli, S., Doglioni, C. (Eds.), J. Virtual Explorer, vol. 36. https://doi.org/10.3809/ jvirtex.2010.00251. Paper 20. Crisci, G.M., De Francesco, A.M., Mazzuoli, R., Poli, G., Stanzione, D., 1989. Geochemistry of recent volcanics of Ischia Island, Italy: evidences for fractional crystallisation and magma mixing. Chem. Geol. 78, 15e33. D’Antonio, M., Di Girolamo, P., 1994. Petrological and geochemical study of mafic shoshonitic volcanics from Procida-Vivara and Ventotene islands (Campanian Region, South Italy). Acta Vulcanol. 5, 69e80. D’Antonio, M., Civetta, L., Di Girolamo, P., 1999. Mantle source eterogeneity in the Campanian region (south Italy) as inferred from geochemical and isotopic features of mafic volcanic rocks with shoshonitic affinity. Mineral. Petrol. 67, 163e192. D’Antonio, M., Tonarini, S., Arienzo, I., Civetta, L., Dallai, L., Moretti, R., Orsi, G., Andria, M., Trecalli, A., 2013. Mantle and crustal processes in the magmatism of the Campania region: inferences from mineralogy, geochemistry, and SrNd-O isotopes of young hybrid volcanics of the Ischia island (South Italy). Contrib. Mineral. Petrol. 165, 1173e1194. D’Antonio, M., 2011. Lithology of the basement underlying the Campi Flegrei caldera: volcanological and petrological constraints. J. Volcanol. Geotherm. Res. 200, 91e98. Dallai, L., Cioni, R., Boschi, C., D’Oriano, C., 2011. Carbonate-derived CO2 purging magma at depth: influence on the eruptive activity of SommaVesuvius, Italy. Earth Planet. Sci. Lett. 310, 84e95. D’Antonio, M., Tonarini, S., Arienzo, I., Civetta, L., Di Renzo, V., 2007. Components and processes in the magma genesis of the Phlegrean Volcanic District, southern Italy. In: Beccaluva, L., Bianchini, G., Wilson, M. (Eds.), Cenozoic Volcanism in the Mediterranean Area: Geol. Soc. Am. Spec. Paper, vol. 418, pp. 203e220. De Astis, G., Peccerillo, A., Kempton, P.D., La Volpe, L., Wu, T.W., 2000. Transition from calc-alkaline to potassium-rich magmatism in subduction environments: geochemical and Sr, Nd, Pb isotopic constraints from the island of Vulcano (Aeolian arc). Contrib. Mineral. Petrol. 139, 684e703. De Astis, G., Pappalardo, L., Piochi, M., 2004. Procida volcanic history: new insights into the evolution of the Phlegraean Volcanic District (Campania region, Italy). Bull. Volcanol. 66, 622e641. De Astis, G., Kempton, P.D., Peccerillo, A., Wu, T.W., 2006. Trace element and isotopic variations from Mt. Vulture to Campanian volcanoes: constraints for slab detachment and mantle infl ow beneath southern Italy. Contrib. Mineral. Petrol. 151, 331e351. De Natale, G., Troise, C., Pingue, F., Mastrolorenzo, G., Pappalardo, L., 2006. The Somma-Vesuvius volcano (Southern Italy): structure, dynamics and hazard evaluation. Earth Sci. Rev. 74, 73e111. De Siena, L., Del Pezzo, E., Bianco, F., 2010. Seismic attenuation imaging of Campi Flegrei: evidence of gas reservoirs, hydrothermal basins and feeding systems. J. Geophys. Res. 115, B09312. https://doi.org/10.1029/2009JB006938. De Vivo, B., Rolandi, G., Gans, P.B., Calvert, A., Bohrson, W.A., Spera, F.J., Belkin, H.E., 2001. New constraints on the pyroclastic eruptive history of the Campanian volcanic plain (Italy). Mineral. Petrol. 73, 47e65. De Vivo, B., Petrosino, P., Lima, A., Rolandi, G., Belkin, H.E., 2010. Research progress in volcanology in the Neapolitan area, Southern Italy: a review and some alternative views. Mineral. Petrol. 99, 1e28.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Deino, A.L., Orsi, G., de Vita, S., Piochi, M., 2004. The age of the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei caldera Italy) assessed by 40Ar/39Ar dating method. J. Volcanol. Geotherm. Res. 133, 157e170. Di Girolamo, P., Stanzione, D., 1973. Lineamenti geologici e petrologici dell’Isola di Procida. Rend. Soc. Ital. Min. Petr. 29, 81e125. Di Girolamo, P., 1978. Geotectonic settings of Miocene Quaternary volcanism in and around the eastern Tyrrhenian Sea border (Italy) as deduced from major element geochemistry. Bull. Volcanol. 41, 229e250. Di Renzo, V., Di Vito, M.A., Arienzo, I., Carandente, A., Civetta, L., D’Antonio, M., Giordano, F., Orsi, G., Tonarini, S., 2007. Magmatic history of SommaVesuvius on the basis of new geochemical and isotopic data from a deep borehole (Camaldoli della Torre). J. Petrol. 48, 753e784. Di Renzo, V., Arienzo, I., Civetta, L., D’Antonio, M., Tonarini, S., Di Vito, M.A., Orsi, G., 2011. The magmatic feeding system of the Campi Flegrei caldera: architecture and temporal evolution. Chem. Geol. 281, 227e241. Esposito, R., Bodnar, R.J., Danyushevsky, L., De Vivo, B., Fedele, L., Hunter, J., Lima, A., Shimizu, N., 2011. Volatile evolution of magma associated with the Solchiaro eruption in the Phlegrean Volcanic District (Italy). J. Petrol. 52, 2431e2460. Esposito, R., Badescu, K., Steele-MacInnis, M., Cannatelli, C., De Vivo, B., Lima, A., Bodnar, R.J., Manning, C.E., 2018. Magmatic evolution of the Campi Flegrei and Procida volcanic fields, Italy, based on interpretation of data from well-constrained melt inclusions. Earth Sci. Rev. 185, 325e356. Fedele, L., Morra, V., Perrrotta, A., Scarpati, C., 2006. Volcanological and geochemical features of the products of the Fiumicello eruption, Procida island, Campi Flegrei (Southern Italy). Per. Min. 75, 43e71. Fedele, L., Scarpati, C., Lanphere, M., Melluso, L., Morra, V., Perrotta, A., Ricci, G., 2008. The Breccia Museo formation, Campi Flegrei, southern Italy: geochronology, chemostratigraphy and relationship with the Campanian Ignimbrite eruption. Bull. Volcanol. 70, 1189e1219. Fowler, S.J., 2019. Petrogenesis of Campanian ignimbrites: a review. In: De Vivo, B., Belkin, H.E., Rolandi, G. (Eds.), Vesuvius, Campi Flegrei, and Campanian Volcanism. Geology, Petrology, and Related Risk. Elsevier (This book). Francalanci, L., Peccerillo, A., Poli, G., 1987. Partition coefficients of minerals in potassium-rich rocks: data from the Roman province. Geochem. J. 21, 1e10. Fulignati, P., Marianelli, P., Santacroce, R., Sbrana, A., 2000. The skarn shell of the 1944 Vesuvius magma chamber. Genesis and P-T-X conditions from melt and fluid inclusion data. Eur. J. Mineral. 12, 1025e1039. Gale, A., Dalton, C.A., Langmuir, C.H., Su, Y., Schilling, J.-G., 2013. The mean composition of ocean ridge basalts. Gechem. Geophys. Geosyst. 14 https:// doi.org/10.1029/2012GC004334. louk, P., Gasperini, D., Blichert-Toft, J., Bosch, D., Del Moro, A., Macera, P., Te de, F., 2000. Evidence from Sardinian basalt geochemistry for recycling Albare of plume heads into the Earth’s mantle. Nature 408, 701e704. de, F., Gasperini, D., Blichert Toft, J., Bosch, D., Del Moro, A., Macera, P., Albare 2002. Upwelling of deep mantle material through a plate window: evidence from the geochemistry of Italian basaltic volcanics. J. Geophys. Res. 107 (B12), 2367. https://doi.org/10.1029/2001JB000418.

115

116

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Gebauer, S.K., Schmitt, A.K., Pappalardo, L., Stockli, D.F., Lovera, O.M., 2014. Crystallization and eruption ages of Breccia Museo (Campi Flegrei caldera, Italy) plutonic clasts and their relation to the Campanian Ignimbrite. Contrib. Mineral. Petrol. 167, 953. Gillot, P.-Y., Chiesa, S., Pasquare, G., Vezzoli, L., 1982. 512 AD to 1139 AD 4 interplinian eruptions

303 AD No chronologic distribution

700 BC From 1758 BC to 832 BC 3 interplinian eruptions

Repose Time 6000 years

OLDER SOMMA ACTIVITY

Figure 6.2 Plinian and interplinian volcanic activity of Mt. SommaeVesuvius, subdivided in megacycles as defined by Ayuso et al. (1998). Blue, first megacycle; green, third megacycle; pink, second megacycle. Eruptive events show nomenclature by Rolandi et al. (1998, 2004) and that in parentheses by Santacroce (1987). Ages of eruptions and repose time are as reported in Rolandi et al. (1998) and Santacroce et al. (2008).

Chapter 6 Tracing magma evolution at Vesuvius volcano

The second megacycle (8e2.7 ka) includes plinian eruptions known as Ottaviano (8 ka, also labeled as Mercato by Santacroce, 1987) and Avellino (3.5 ka), as well as Protohistoric interplinian events (between 3.5 and 2.7 ka) (Fig. 6.2). The third megacycle (79e1944 AD) includes Pompeii (79 AD) and Pollena (472 AD) plinian eruptions, subplinian eruptions, such as the 1631 AD event, and small-scale effusive and explosive events belonging to the Ancient Historic (79e472 AD), Medieval interplinian (472e1631 AD), and Recent interplinian activity (1631e1944 AD) (Fig. 6.2). Each magmatic megacycle is followed by a long repose time (Fig. 6.2), and a new magmatic megacycle (composing of several smaller cycles) always starts with a plinian eruption. The third megacycle started with the 79 AD plinian eruption after w800 years of repose, and within this megacycle, plinian and subplinian eruptions occurred in 472 and 1631 AD, respectively. These events occurring at the beginning and within the third megacycle were followed by weakly to moderately explosive or explosive-effusive interplinian eruptions that ended with a repose period (De Vivo et al., 2010 and references therein). SV is now in a quiescent state, with activity expressed by only fumaroles and low-magnitude seismic activity. Some authors have associated this state of repose with progressive cooling of a residual magma body at shallow depths (Scandone et al., 2008) or within the volcanic conduit (De Natale et al., 2003). The nature of the magmatic plumbing system of SV is still a matter of intense debate. Some authors support the existence of a shallow magma body (w1.5e2.0 km depth) based on seismic tomography (Zollo et al., 1996, 1998; De Natale et al., 1998, 2003) and aeromagnetic data (Fedi et al., 1998). Other authors (Belkin et al., 1985; Belkin and De Vivo, 1993) have used fluid inclusions (FIs) data from xenoliths to constrain the depths of magma ponding at 3.5e10 km and >12 km depth (Fig. 6.3), with no evidence of shallower magma levels. Intermediate magma storage is confirmed by seismic (Auger et al., 2001; Zollo et al., 1996) and magnetotelluric evidence (Di Maio et al., 1998) that shows there is an active large magma chamber at depths of 8e10 km (Fig. 6.3). Scaillet et al. (2008) proved by phase equilibria calculations that the SV reservoir migrated from 9e11 km to 3e4 km in the last 18.5 ka. A magma chamber deeper than 12 km and perhaps extending to 30 km has been proposed by De Natale et al. (2001, 2006), who interpreted a high velocity body dipping westward from 65 km down to w 300 km as a subducted plate within the mantle. Data from deep (300 km) seismicity studies (Anderson and Jackson,

123

Chapter 6 Tracing magma evolution at Vesuvius volcano

Age < 79 AD 12 km. Modified from De Vivo, B., Petrosino, P., Lima, A., Rolandi, G., Belkin, H.E., 2010. Research progress in volcanology in Neapolitan area, Southern Italy: a review and alternative views. Mineral. Petrol. 99, 1e28.

1987; Milano et al., 1994; Faccenna et al., 2001; Billi et al., 2007) suggest there is an actively subducting slab in the central Tyrrhenian Sea. Danyushevsky and Lima (2001) postulate that the source of the Breccia Museo mafic xenoliths at Campi Flegrei could be genetically related to the pre-14 ka SV volcanic system, with the link most likely established before the emplacement of the Neapolitan Yellow Tuff (15 ka, Deino et al., 2004). Possible reactivity of SV might be triggered by the arrival of rapidly ascending magma batches forming a new shallow magma level (Aulinas et al., 2008; Principe and Marini, 2008; Scandone et al., 2008). The arrival of this new cooler magma would increase fumarole activity, produce hydrothermal explosions, and trigger earthquakes, which would provide forecasting information for the future reawakening of SV. The link between tectonic activity and volcanic eruptions at SV was suggested by Morgan et al. (2006), who modeled trace element concentration changes in sanidine from the Pompeii eruption (79 AD). These authors related Ba diffusion profiles measured in sanidine to episodic

Chapter 6 Tracing magma evolution at Vesuvius volcano

recharge events in the magmatic reservoir using a year-to-decade scale. Morgan et al. (2006) suggest that the Ba diffusion profiles can be coupled to two distinct recharge events, 22 and 15 years before the 79 AD eruption, and associate the events with the magnitude 5.7e5.9 earthquake that occurred in 62 AD.

Magma evolution at SommaeVesuvius volcano Several studies on magma evolution (Joron et al., 1987; Trigila and De Benedetti, 1993; Marianelli et al., 1995; Cioni et al., 1998; Lima et al., 1999; Raia et al., 2000; Webster et al., 2001; Aulinas et al., 2008; Pappalardo and Mastrolorenzo, 2010; Dallai et al., 2011; Redi et al., 2017 and references therein) have suggested that the crystallization and fractionation of clinopyroxene (Cpx) and olivine (Ol) are the controlling factors in the evolution of parental melts beneath SV. These studies focused on specific SV eruptions rather than the entire volcanic history of SV. Only Redi et al. (2017) have studied the full range of eruptive products, including Cpx and Ol mineral compositions linked to volcanic products younger than 40 ka. The selected time span is considered to be the most representative of the volcanic system as all SV products are younger than the Campanian Ignimbrite deposit (w40 ka, Giaccio et al., 2008) and Mt. Somma formed as a stratovolcano only after w40 ka (Brocchini et al., 2001; Santacroce and Sbrana, 2003). The SV volcanic complex has produced rocks that range from shoshonite to trachy-phonolite and from alkali-basalt to tephrite and phonolite (Fig. 6.4). The degree of silica undersaturation increases through time, and rocks with the lowest SiO2 content belong to the third megacycle (Fig. 6.4). Volcanic products of SV have been petrographically described by many authors (Rosi and Santacroce, 1983; Joron et al., 1987; Santacroce et al., 1993; Marianelli et al., 1999). Medium silica-undersaturated rocks older than 472 AD contain phenocrysts of Cpx as well as microlite, plagioclase (Pl), FeeTi oxides (Ox), biotite (Bio), and apatite (Ap), in order of abundance. In the least evolved rocks, Ol appears as phenocrysts. In the most evolved rocks, leucite (Leu) appears as microlite and microphenocrysts, while K-feldspar (K-fsp) is only present as phenocrysts. Leucite is absent in rocks ranging from shoshonites to trachytes of the first megacycle. Nepheline (Neph) is the only feldspathoid in the Avellino volcanic products. High-silica undersaturated rocks of the third megacycle are porphyritic with abundant Cpx and Leu, an average amount of Ox and Ap and a minor or rare amount of Pl, Bio, and K-fsp.

125

Chapter 6 Tracing magma evolution at Vesuvius volcano

16 st

1 mega-cycle

Phonolite

14

2

nd

mega-cycle

rd

3 mega-cycle

Tephriphonolite

12

Trachyte

Na2O+K2O

126

10

Nephelinite or Melilitite

PhonoTephrite

Trachyandesite

8 Tephrite or Basanite Trachybasalt

6

Trachydacite Rhyolite

Basaltic trachyandesite Dacite

4

Basalti anddesite

Basalt

2 0 35

Andesite

Picrobasalt

40

45

50

55 SiO2

60

65

70

75

Figure 6.4 Total alkali (Na2O þ K2O)esilica (SiO2) diagram (Le Bas et al., 1986) showing distribution of Mt. SommaeVesuvius bulk rock samples. Fields are obtained by using data from Piochi et al. (2006). Blue field, first megacycle; green field, third megacycle; pink field, second megacycle.

Bulk rock Sr and Nd isotope compositions from Sarno (18 ka), Avellino (3.55 ka), Pompeii (79 AD), and Pollena (472 AD) range from w0.7062 to w0.7078 and 0.51225 to 0.51257, respectively (Civetta et al., 1991; Civetta and Santacroce, 1992; Cioni et al., 1995; Ayuso et al., 1998; Bertagnini et al., 1998; Somma et al., 2001; Chapter 5), suggesting there was a chemically and isotopically zoned magma chamber located within the carbonate platform (Barberi and Leoni, 1980; Del Moro et al., 2001). According to Chapter 5, several processes have affected magmas during SV evolution, such as fractional crystallization, magma mixing and recharge, and wall rock assimilation. Piochi et al. (2006) suggest that some of these processes, particularly mixing and recharge, occurred repeatedly throughout the volcanic history of SV and were more prevalent during interplinian activity (250, 1000, 2500, and 15,000 years BP), as shown by the variation of 87 Sr/86Sr of erupted magmas with age (Fig. 6.5).

Melt inclusions Melt inclusions (MIs) are small portions of silicate melt that are trapped in surface irregularities or defects of host crystals during growth in a magma body (e.g., Cannatelli et al., 2016 and references therein). The MIs typically contain variable amounts of daughter crystals, glass, and/or vapor and are very common in volcanic rocks. MIs represent time capsules created during

Chapter 6 Tracing magma evolution at Vesuvius volcano

Figure 6.5 87Sr/86Sr versus age of eruption for Mt. SommaeVesuvius rocks. Circles, first megacycle; diamonds, second megacycle; squares, third megacycle; triangles, transitional period. Closed symbols represent data from plinian eruptions; open symbols represent compositions of interplinian rocks. Modified from Piochi, M., Ayuso, R.A., De Vivo, B., Somma, R., 2006. Crustal contamination and crystal entrapment during polybaric magma evolution at Mt. SommaVesuvius volcano, Italy: geochemical and Sr isotope evidence. Lithos 86, 303e329.

degassing or magma differentiation and allow researcher to trace the evolution of magma from its formation at mantle depths to its release at the surface (e.g., Cannatelli et al., 2016 and references therein). Several authors have studied MIs hosted in eruptive products of SV (Table 6.1), obtaining a wide range of chemical composition data (Fig. 6.6). The first studies of FIs and MIs of SV were undertaken by Roedder (1965), who investigated the 1858 and 1944 AD lavas for the presence of CO2 FIs in Cpx and Leu phenocrysts and observed very small shrinkage bubbles in small (1600 C) homogenization temperatures, suggesting that mass leakage occurred during the experiment (Bazarova and Krasnov, 1975). Sobolev et al. (1972) measured a gas content of 23.3 vol% CO2 þ 76.8 vol % N2 þ rare gases (vol%) for Leu-hosted Mis and 0.4 vol% CO2 þ 91.6 vol% N2 þ rare gases(vol%) for the Cpx-hosted MIs. One of the first studies of Vesuvius samples that used MIs to determine the geochemistry of the preeruptive magma was conducted by Barberi et al. (1981). In this work, the authors determined that the phonolitic pumice ejected during the two most recent and important plinian eruptions of Vesuvius (Avellino and Pompeii, Fig. 6.2) originated from the fractionation of a

127

Table 6.1 Studies on melt inclusions in volcanic rocks from Mt. SommaeVesuvius. Methods

Results

References

Year Host(s)

Raman/ P-T Melt Petrography Heating EMPA SIMS LAICPMS FTIR conditions evolution

Roedder Sobolev et al. Barberi et al. Belkin et al. Cortini et al.

1965 1972 1981 1985 1985

X X X X X

X X X X

Vaggelli et al. Vaggelli et al. Marianelli et al. Belkin et al. Cioni et al. Lima et al. Marianelli et al. Raia et al. Webster et al. Fulignati et al.

1992 1992 1995 1998 1998 1999 1999 2000 2001 2001

X X X X X X X X X X

X X X X X X X X X X

Fulignati et al. Schiano et al. Fulignati et al. Fulignati and Marianelli Lima et al. Balcone-Boissard et al. Balcone-Boissard et al. Klebesz et al.

2004 2004 2007 2007

X X X X

X

2007 Ol, Cpx 2008 Cpx, Fsp

X X

X

2012 Cpx, Fsp

X

2012 Cpx

X

Leu Cpx, Leu Leu, Cpx, Ol Cpx Cpx, Ol, Sp, Mica Cpx, Fsp Cpx, Fsp Ol, Cpx Cpx, Fsp Cpx, Fsp Cpx, Fsp Cpx, Ol, Leu Cpx Cpx Neph, Fsp, Leu, Cpx Ol, Fsp Ol Cpx, Fsp Cpx, Fsp

Volatiles

X X X

X X

X X X X X X X X X X X X X X X

X X

X X

X

X X X X X

X

X

X X

X X

X X

X

X X

X

X X X X X X X X X X X X

X X X X X X X

X X X

X

X X

X

X X

X

X

X

X X

Cpx, clinopyroxene; EMPA, Electron Microprobe Analysis; Fsp, feldspar; FTIR, Fourier Transform Infrared Spectroscopy; LAICPMS, Laser Ablation Inductively Coupled Plasma Mass Spectrometry; Leu, leucite; Neph, nepheline; Ol, olivine; Sal, salite; SIMS, Secondary Ion Mass Spectrometry; Sp, spinel.

Chapter 6 Tracing magma evolution at Vesuvius volcano

16 14

Na2O + K2O

12 10

Nephelinite Trachydacite

Rhyolite

8 Tephrite

6

Dacite

4 Basalt

Andesite

Picrobasalt

2 0

Basaltic Andesite

35

40

45

50

55

60

65

70

75

Si2O

Figure 6.6 Color coding as in Fig. 6.5. Circles, pre-Avellino; diamonds, Avellino; squares, 79 AD; stars, Medieval Age; tilted crosses, Modern Age; vertical crosses, 472 AD. Data from studies in Table 6.1.

parental (tephritic) magma in a shallow (w2e4 km) cylindrical chamber located within the Mesozoic limestone that represents the sedimentary basement of the volcano (Fig. 6.7). According to Barberi et al. (1981), the parental magma underwent w70% fractionation and interacted at 800 C (Avellino) and 850 C (Pompeii) with the calcareous country rock, producing skarns whose solids were partly incorporated into the magma. Belkin et al. (1985) and Cortini et al. (1985) suggest that nodules from the skarns underwent a multistage crystallization history based on FIs and MIs data. Belkin et al. (1985) concluded that the skarn nodules formed by crystallization of magma from a peripheral assimilation zone contaminated with the carbonate country rock (Fig. 6.7). Two types of MIs were observed in the skarns, suggesting that at least locally, different melt compositions were present at the same time but most likely at different depths (between 3.5 and 13 km) based on the bimodal CO2 density distribution of FIs (Fig. 6.3). In a later study, Fulignati et al. (2001) concluded that nephelineand K-feldsparehosted MIs represent the NaeKeCa carbonatee chloride melt formed as a result of the interaction between early high-temperature hypersaline fluids (Gilg et al., 2001) and carbonate country rocks, which create an immiscibility process that leads besz et al. to the formation of intrusion-related skarn systems. Kle (2012) shed new light on the nature of the skarns, indicating that Cpx-hosted MIs in the skarn nodules represent samples from the mush zone of the active plumbing system of SV.

129

130

Chapter 6 Tracing magma evolution at Vesuvius volcano

SW Trecase 0

2.5 Km NE SV Pyroclastic deposits

Sandstones and Siltstones

Moderate Salinity

Hydrostatic Pf

Brine + Steam

id d Ol

Ma

Pf

gm

tic

at

ic

ta

os

Flu

th

Limestones and Dolostones

Depth (Km)

Li

s

–4

Magma Body

–8

Thrust Fault

NW

SE Trecase

Clastic and volcanoclastic Quaternary deposits

–12

Low Velocity Zone

Meso-Cenozoic fold thrust belt Low velocity Zone

Figure 6.7 Stratigraphic successions below Mt. SommaeVesuvius and zone of transition from lithostatic to hydrostatic conditions. The area of transition between brittle to plastic is a self-sealed zone with an average P w 1 kbars and depths between 3.6 and 4.5 km (assuming T ¼ 720 C). T and fluid pressure (Pf) gradients are very steep across the interface. Modified from Lima, A., De Vivo, B., Fedele, L., Sintoni, F., Milia, A., 2007. Geochemical variations between the 79 AD and the 1944 AD Somma-Vesuvius volcanic products: constrains on the evolution of the hydrotermal system based on fluid and melt inclusions. Chem. Geol. 237, 401e417.

Chapter 6 Tracing magma evolution at Vesuvius volcano

In the 1980s, researchers primarily concentrated on analyzing major elements in FIs and MIs, while in the 1990s, the majority of studies focused on geochemical composition, including volatiles and trace elements. Vaggelli et al. (1993) analyzed MIs from recent Vesuvius lavas (1631e1944 AD) and pointed out that fractional crystallization was the dominant process during differentiation. However, magma evolution was also affected by convective processes involving Cpx that resulted in normal and/or reverse zoning likely due to inputs of a new primitive unfractionated magma. Marianelli et al. (1995) determined major elements, S, Cl, and H2O content of mafic magma batches that supplied the Vesuvius plumbing system over the last 4000 years. The authors selected Ol- and Cpx-hosted MIs from plinian (Avellino, Pompeii, Pollena) and subplinian (1906e1944 AD) eruptions and determined that K-tephritic H2OeClePeF-rich MIs hosted in the 1906 olivine (Fig. 6.6) likely represent primary magmas of Vesuvius, consistent with a metasomatized mantle origin. Cpx- and Ol-hosted MIs from the other plinan and subplinian eruptive products range from K-basalt to K-tephrite in composition (Fig. 6.6) and represent magma batches that supplied the Vesuvius plinianesubplinian chamber from the Avellino (3.5 ka) and Pollena (472 AD) eruptions (Fig. 6.6). Belkin et al. (1998) studied Cpx-, Ol-, Leu-, and Pl-hosted MIs from the pre-1631 AD products of SV interplinian activity and determined H2O (0.6e2.7 wt%), Cl (up to 1 wt%), F (up to 0.63 wt%), and SO3 (up to 0.5 wt%) content. The authors suggested that the moderately low volatile content of MIs indicate that the nonplinian eruptions at SV were relatively low-energy events. Marianelli et al. (1999) and Cioni et al. (1998) proposed a different evolution for the SV plumbing system during periods of open or closed conduit conditions. When the conduit is open (1906 and 1944 AD eruptions, third cycle, Fig. 6.2), a small magma chamber forms in the upper portions of the volcano (1e2 km depth, Fig. 6.7) and the resident K-tephritic magma forms as a result of several processes (new magma batches, magma mixing, and extractions). When the conduit is closed, larger and deeper (2e5 km) plinian- or subplinian-layered magma chambers form and grow by a periodic arrival of deep magma batches with a deep origin (Fig. 6.7). Cioni et al. (1998) suggested that the increasing volume of the magma chamber is related to changes in the aspect ratio, with the chamber classified as an initial stage or moderate volume chamber (0.01e0.1 km3, 1906 open conduit style), a young stage or medium volume chamber (0.1e0.5 km3, Pollena-type chamber), or a mature stage or large volume chamber (0.5e5 km3, Pompeii-type chamber).

131

132

Chapter 6 Tracing magma evolution at Vesuvius volcano

Marianelli et al. (1999), using MI compositions (major and volatile elements), determined that the magmas feeding the 1944 AD eruption of SV underwent differentiation at different pressures. The authors also suggest that K-tephritic volatile-rich melts (up to 3 wt% H2O, 3000 ppm CO2, and 0.55 wt% Cl) evolved to reach K-phonotephritic compositions (Fig. 6.6) by crystallization of Cpx and Ol at pressures higher than 300 MPa, which involved mixing, open-system degassing, and crystallization of Leu, Cpx, and Pl. According to Marianelli et al. (1999), the eruption was triggered by the input of a volatile-rich magma batch from a depth of 11e22 km into the shallow magma chamber (Fig. 6.7). Lima et al. (1999) studied MIs in scoriae from an SV eruption of Medieval times (Formazione di Terzigno, A.D. 893, Rolandi et al., 1998) and concluded that the MIs have a less evolved magma composition that those reported by Belkin et al. (1998) and Marianelli et al. (1995). Lima et al. (1999) assumed that Cpx-hosted MIs in the Terzigno scoria represented primitive melts similar to those that supply plinian and subplinian magma chambers. They suggest that the polygenetic source of Cpx may indicate that the SV magmatic system retains “records” of the most recent plinian event. The first comprehensive studies (29 chemical components including H2O, S, Cl, F, B, and P2O5) of reheated MIs in products from SV spanning from >14ka to younger than 3.5 ka (Webster et al., 2001) and Medieval products (Raia et al., 2000) provided important constraints on the preeruptive magma geochemistry and eruption behavior relative to magma evolution and evidence for magmatic fluid exsolution occurring well before eruption. Webster et al. (2001) showed there are distinct differences in composition between precaldera rocks (older than 14 ka with magmas slightly enriched in SiO2) and products younger than 3.5 ka (magmas moderately enriched in S, Cl, CaO, MgO, P2O5, F, and many LILE). Furthermore, Webster et al. (2001) determined for the first time that the eruptive behavior at Vesuvius correlates with preeruptive volatile enrichments. These authors indicated that most magmas from explosive plinian and subplinian events