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- Herausgeber: John Wiley & Sons
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- Sprache: Englisch
The Himalaya is well known as the largest and highest mountain belt on Earth. Advances in geoscience over the past few decades have revealed a complex picture of the dynamics of this giant, opening up questions about the initial stages of Himalayan building, lateral variations in its structures, variations in tectonic forcing, tectonic-climate coupling and assessments of the natural hazards affecting this area. In this three-volume book, we present the current knowledge on the building and present-day behavior of the Himalayan range. The objective is not to be exhaustive, but to provide some key elements used by researchers to unravel the many processes acting in the Himalayan dynamics. Mountain environments are at the forefront of climate change with glacier retreat, landslides, flash floods and water availability. Understanding the delicate balance that controls the dynamics of the Himalayan giant is now, more than ever, a major challenge for the scientific community.
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Veröffentlichungsjahr: 2023
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Table of Contents
Cover
Dedication Page
Title Page
Copyright Page
Tributes
Foreword
Preface. From Research to Education: The Example of the Seismology at School in Nepal Program
Part 1: Tectonic Framework of the Himalaya and Tibet
Chapter 1. Plate Reconstructions and Mantle Dynamics Leading to the India–Asia Collision
1.1. Introduction
1.2. The India–Asia convergence and the age of the collision
1.3. Plate collision configurations
1.4. Reconstruction of the Neotethys Ocean closure dynamic
1.5. Conclusion
1.6. References
Chapter 2. Building the Tibetan Plateau During the Collision Between the India and Asia Plates
2.1. Introduction
2.2. Present-day Tibetan crustal deformation
2.3. Tibetan lithospheric mantle subduction during collision
2.4. Modeling the Tibetan plateau formation during the indentation of the Indian continent into Asia
2.5. Conclusion
2.6. References
Chapter 3. The Major Thrust Faults and Shear Zones
3.1. Introduction
3.2. Some basic concepts
3.3. Main faults and shear zones
3.4. Tectonic models
3.5. Conclusion
3.6. References
Part 2: Along Strike Variations
Chapter 4. Seismological Imaging and Current Seismicity of the Himalayan Arc
4.1. Introduction
4.2. Imaging by elastic waves
4.3. Exploring the Central Himalaya along cross-sections
4.4. Lateral variations
4.5. Current seismicity of the Himalaya
4.6. Conclusion
4.7. References
Chapter 5. Gravity Observations and Models Along the Himalayan Arc
5.1. Introduction
5.2. Methods
5.3. Isostasy
5.4. Flexure of the Indian plate
5.5. Satellite data contribution
5.6. Conclusion
5.7. References
Chapter 6. Topographic and Thermochronologic Constraints on the Himalayan Décollement Geometry
6.1. Introduction
6.2. Methods
6.3. Regional case studies
6.4. Discussion
6.5. Conclusion
6.6. References
Part 3: Focus
Chapter 7. Application of Near-surface Geophysical Methods for Imaging Active Faults in the Himalaya
7.1. Introduction
7.2. Near-surface geophysics
7.3. Geophysical results of case study from south Bhutan
7.4. Implications of near-surface geophysical findings
7.5. Conclusion
7.6. References
Chapter 8. Overview of Hydrothermal Systems in the Nepal Himalaya
8.1. Introduction
8.2. Measurement methods
8.3. Summary of results at the hydrothermal sites in the Nepal Himalaya
8.4. Conclusion
8.5. References
Conclusion
List of Authors
Index
Summary of Volume 2
Summary of Volume 3
End User License Agreement
List of Illustrations
Chapter 1
Figure 1.1. Gondwana configuration before the Atlantic Ocean opening. Redrawn ...
Figure 1.2. Examples of the spreading rate and direction of the Central Indian...
Figure 1.3. India–Asia collision. The yellow parts of the continents are preci...
Figure 1.4. Paleogeographic reconstructions according to the three main models...
Figure 1.5. Cross-sectional view of the India–Asia convergent zone during the ...
Figure 1.6. Transition from continental subduction (A) to India underplating A...
Chapter 2
Figure 2.1. Topographic profiles across some mountain ranges of the Earth (mod...
Figure 2.2. GPS velocity field over the Tibetan Plateau considering Eurasia as...
Figure 2.3. (a) Kinematics of active tectonics in Tibet represented from GPS v...
Figure 2.4. Crustal and lithospheric structure beneath Tibet. (a) TIPAGE seism...
Figure 2.5. Identification of metasomatized lithospheric mantle beneath Centra...
Figure 2.6. Analogue model of the subduction of the Tibetan lithosphere due to...
Figure 2.7. Subduction dynamics of an heterogeneous plate (modified from Capit...
Chapter 3
Figure 3.1. Simplified geologic map of the Himalaya and southern Tibet. After ...
Figure 3.2. Geologic cross-sections. (a) Western Bhutan. After Kellett and Gru...
Figure 3.3. Qomolangma detachment. Notice the Yellow bands and the darker Ever...
Figure 3.4. Structures from the South Tibetan detachment system. (a) Lhotse de...
Figure 3.5. Compilation of age data constraining the timing of activity of the...
Figure 3.6. Structures from the main central thrust zone. (a) Sharp contact be...
Figure 3.7. Optically measured quartz c-axis fabrics and recrystallization mic...
Figure 3.8. Kakhtang thrust in north-central Bhutan. This and equivalent struc...
Figure 3.9. Main boundary thrust. (a) Gondwana coal-bearing clastic sandstone ...
Figure 3.10. Trace of the main frontal thrust along the border between Bhutan ...
Figure 3.11. Main frontal thrust. (a) Natural outcrop along the river bank in ...
Figure 3.12. Jomolhari (also Chomolhari; 7326 m) on the western border of Bhut...
Figure 3.13. Coeval partial melting and deformation in the GHS. (a) Migmatite ...
Figure 3.14. Stress distribution in the Himalaya and Tibet. (a) Simple elastic...
Figure 3.15. Diagram of the flow pattern in a channel with μh > μc > μf. The v...
Chapter 4
Figure 4.1. Main elements of seismic imaging, from source to receivers. (a) Ac...
Figure 4.2. Map of seismological data coverage of the Himalaya–Tibet system. R...
Figure 4.3. Interpretative cross-section of the INDEPTH experiment results, a ...
Figure 4.4. Migrated P-to-S converted waves’ cross-section along 85°E from pro...
Figure 4.5. Synoptic cross-section of the Himalaya–Tibet collision zone at its...
Figure 4.6. Compilation of Moho and MHT geometry across the Himalaya at variou...
Figure 4.7. Schematic cartoon on how the Indian mantle lithosphere may be torn...
Figure 4.8. Present-day geometry of the subducting Indian plate that differs b...
Figure 4.9. A compilation of earthquakes from multiple, high-quality open cata...
Chapter 5
Figure 5.1. Gravimetric corrections associated with a north–south measurement ...
Figure 5.2. Simplified diagram of a Bouguer anomaly profile associated with a ...
Figure 5.3. Isostasy compensation models. (a) Local compensation in the Pratt ...
Figure 5.4. Bouguer anomaly map of the Himalaya and surrounding regions. (e.g....
Figure 5.5. Geometry of lithospheric structures and density distribution acros...
Figure 5.6. Bouguer anomaly profiles between western Nepal and eastern Bhutan ...
Figure 5.7. Map of gravity gradients including topographic corrections from th...
Figure 5.8. Three-dimensional model showing the geometry of the Indian lithosp...
Chapter 6
Figure 6.1. Overview map of the Himalaya showing main geological units and fau...
Figure 6.2. Three representative structural cross-sections based on structural...
Figure 6.3. Normalized channel-steepness index for main rivers and their tribu...
Figure 6.4. Thermochronologic systems and their interpretation using thermal-k...
Figure 6.5. Conceptual sketches of different kinematics that have been used to...
Figure 6.6. (A) Available thermochronology data and (B) structural cross-secti...
Figure 6.7. Map of published thermochronology data from western and central Ne...
Figure 6.8. Simplified geological structure (lower panels; after Jouanne et al...
Figure 6.9. Map of published thermochronology data from the north-western, Kin...
Figure 6.10. Map of published thermochronology data from Bhutan and western Ar...
Figure 6.11. Transects across western and eastern Bhutan showing – upper panel...
Chapter 7
Figure 7.1. (a) Location of the Kingdom of Bhutan and the study area in south ...
Figure 7.2. Location of both the Electrical Resistivity Tomography (ERT) surve...
Figure 7.3. 2D 5m-spacing dipole–dipole ERT model (top) and Wenner–Schlumberge...
Figure 7.4. Seismic data acquisition layout plan. For a color version of this ...
Figure 7.5. Top: (a) seismic tomographic refraction image showing the velocity...
Figure 7.6. Measured gravity (top), elevation (middle) and gravity variations ...
Figure 7.7. Geometry of the model used in the stochastic inversion. STL – Sout...
Figure 7.8. Misfit between observed and calculated ERT pseudo-sections for ele...
Figure 7.9. Distribution of TFT dip angle from ERT sections using both dipole–...
Figure 7.10. Misfit between observed and calculated time delay corresponding t...
Figure 7.11. Distribution of TFT dip angle obtained from seismic measurements....
Figure 7.12. a) Comparison between observed (blue circles) and calculated (gra...
Figure 7.13. Simplified cross-section showing the main geophysical results obt...
Chapter 8
Figure 8.1. Map of the Nepal geothermal belt. The currently identified geother...
Figure 8.2. Pictures of selected hydrothermal sites in Far-Western, Mid-Wester...
Figure 8.3. Pictures of selected hydrothermal sites in Central and Eastern Nep...
Guide
Cover Page
Series Page
Title Page
Copyright Page
Tributes
Foreword
Preface
Table of Contents
Begin Reading
Conclusion
List of Authors
Index
Summaries of other volumes
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In memory of distinguished professorsM. Gaetani, P. Molnar and A. Steck
SCIENCES
Geoscience, Field Director – Yves Lagabrielle
Dynamics of the Continental Lithosphere,Subject Head – Sylvie Leroy
Himalaya, Dynamics of a Giant 1
Geodynamic Setting of the Himalayan Range
Coordinated by
Rodolphe Cattin
Jean-Luc Epard
First published 2023 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUKwww.iste.co.uk
John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USAwww.wiley.com
© ISTE Ltd 2023The rights of Rodolphe Cattin and Jean-Luc Epard to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.
Library of Congress Control Number: 2022948342
British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN 978-1-78945-129-0
ERC code:PE10 Earth System Science PE10_5 Geology, tectonics, volcanology
Tributes
In the past five years, three of our friends, colleagues and mentors Maurizio Gaetani, Peter Molnar and Albrecht Steck have passed away. Their outstanding contribution to the knowledge of the Himalayan range has influenced many authors of this book. We pay tribute to them in the following paragraphs. We dedicate this book to these three exceptional professors.
The mountains of Asia, and the charm of romantic geology – A tribute to the legacy of Maurizio Gaetani (1940–2017) by Eduardo Garzanti
Student of Ardito Desio, organizer of the 1954 Italian conquest of K2 and younger colleague of Riccardo Assereto, killed by a landslide during the second Friuli earthquake of September 9, 1976, the everlasting love of Maurizio Gaetani for Asian geology began in 1962, with his Thesis fieldwork in the Alborz Mountains of Iran. During summer 1977, as Ladakh opened to foreigners, Maurizio first discovered with Alda Nicora the Cretaceous/Triassic boundary in the Zanskar Range. On August 1, 1981, we took a bus from Delhi to Lahul and crossed with horses and horsemen the Baralacha La and Phirtse La to describe the stratigraphy of the Paleozoic–Eocene succession of the Tethys Himalaya. New expeditions were led by Maurizio to Zanskar in 1984 and 1987 to reconstruct the paleogeographic history of northern India, from the newly identified Early Paleozoic Pan-African orogeny to Upper Paleozoic Neotethyan rifting and the subsequent Mesozoic passive-margin evolution terminated with early Paleogene collision with the Asian arc-trench system.
In the meanwhile, Maurizio’s Karakorum adventure had begun with the 1986 expedition to the Hunza Valley. From then on, Maurizio’s unique dedication to Karakorum geology is testified by 10 expeditions he led to Chitral, Wakhan, Shimshal and Shaksgam, during which every meter of the stratigraphic section from Ordovician to Cretaceous was measured to reconstruct the opening of Paleotethys and Neotethys and their subsequent closure during early and late Mesozoic orogenies. The amazing amount of work carried out during these surveys is condensed in the magnificent geological map of North Karakorum and summarized in his last paper “Blank on the Geological Map”. The legacy of Maurizio Gaetani is to remind us that, no matter how much technology is involved, any scientific adventure is primarily a romantic adventure.
Maurizio Gaetani has contributed to about 50 articles published in peer review journals. Here is a list of his major contributions:
Gaetani, M. (2016). Blank on the geological map. Rendiconti Lincei, 27(2), 181–195.
Gaetani, M. and Garzanti, E. (1991). Multicyclic history of the northern India continental margin (northwestern Himalaya). AAPG Bulletin, 75(9), 427–1446.
Gaetani, M., Nicora, A., Premoli Silva, I. (1980). Uppermost Cretaceous and Paleocene in the Zanskar range (Ladakh-Himalaya). Rivista Italiana di Paleontologia e Stratigrafia, 86(1), 127–166.
Gaetani, M., Garzanti, E., Jadoul, F., Nicora, A., Tintori, A., Pasini, M., Khan, K.S.A. (1990). The north Karakorum side of the Central Asia geopuzzle. Geological Society of America Bulletin, 102(1), 54–62.
Zanchi, A. and Gaetani, M. (2011). The geology of the Karakoram range, Pakistan: The new 1: 100,000 geological map of Central-Western Karakoram. Italian Journal of Geosciences, 130(2), 161–262.
Always on the cutting edge and looking for new ideas to advance Earth Sciences – Peter Molnar (1943–2022) by Vincent Godard, Rodolphe Cattin and György Hetényi
In the final phase of preparing the three volumes of this book, we sadly learned of the passing of Peter Molnar. Peter was a giant of the Earth Sciences, whose contributions would be too long to list exhaustively in this tribute; he left a remarkably enduring mark on Himalaya–Tibet research.
Peter’s scientific career began at a pivotal moment for Earth Sciences. He has significantly contributed to developing and applying the new paradigm of Plate Tectonics. Using innovative approaches based on tectonics, seismology, paleomagnetism and satellite imagery, Peter revolutionized our understanding of continental deformation and lithosphere behavior. Although Peter worked on a wide range of problems and geoscientific contexts, the India–Asia collision and the dynamics of the Himalaya–Tibet system have very often been at the core of his investigations. He has left a lasting imprint on research in this region, particularly by his desire to understand the mechanical processes at work during the deformation of this orogenic system.
Consistent with his comprehensive and integrated approach to geodynamic problems, Peter explored a wide range of ideas and processes related to the Himalaya–Tibet system’s global role, and initiated several ideas and research directions that are still active today. One example, among many, is the study of the physical relationships and interaction of mechanisms between the development of Tibet’s topography and the Southeast Asian monsoon regime. Among the research fields initiated by Peter, understanding the relationships between erosion, tectonics and climate is undoubtedly one of the most innovative and impactful for our community. Following a series of seminal articles by Peter and his colleagues, the complex interactions between the processes responsible for topographic relief creation and destruction are still actively debated in the Himalaya. Peter’s research always focused on a global understanding of these processes, particularly those responsible for the variations in erosion and global sedimentary fluxes related to the evolution of Himalayan orogeny and the late Cenozoic evolution of climate. The fact that so many of these topics are still at the forefront of current research by so many groups worldwide is a major testimony to Peter Molnar’s prescience on the dynamics of the Himalaya–Tibet system.
Beyond these outstanding contributions, Peter will be remembered for his great sense of humor and for having always been accessible and available to discuss new ideas with young scientists.
Peter Molnar has contributed to an impressive number of publications, some of which have been milestones in the understanding of the Tibet–Himalaya system:
Bilham, R., Gaur, V.K., Molnar, P. (2001). Himalayan seismic hazard.Science, 293(5534), 1442–1444.
Gan, W., Molnar, P., Zhang, P., Xiao, G., Liang, S., Zhang, K., Li, Z., Xu, K., Zhang, L. (2022). Initiation of clockwise rotation and eastward transport of southeastern Tibet inferred from deflected fault traces and GPS observations. Geological Society of America Bulletin, 134(5–6), 1129–1142.
Houseman, G.A., McKenzie, D.P., Molnar, P. (1981). Convective instability of a thickened boundary layer and its relevance for the thermal evolution of continental convergent belts. Journal of Geophysical Research: Solid Earth, 86(B7), 6115–6132.
Molnar, P. (2012). Isostasy can’t be ignored. Nature Geoscience, 5(2), 83–83.
Molnar, P. and England, P. (1990). Late Cenozoic uplift of mountain ranges and global climate change: Chicken or egg? Nature, 346(6279), 29–34.
Molnar, P. and Tapponnier, P. (1975). Cenozoic Tectonics of Asia: Effects of a continental collision: Features of recent continental tectonics in Asia can be interpreted as results of the India-Eurasia collision. Science, 189(4201), 419–426.
Zhang, P.Z., Shen, Z., Wang, M., Gan, W., Bürgmann, R., Molnar, P., Wang, Q., Niu, Z., Sun, J., Wu, J. et al. (2004). Continuous deformation of the Tibetan Plateau from global positioning system data. Geology, 32(9), 809–812.
Geology of the Indian Himalaya – Albrecht Steck (1935–2021) by Jean-Luc Epard and Martin Robyr
Albrecht Steck was the main driving force behind the Himalayan geological research program led at the University of Lausanne over the last 40 years. His work has focused on the Indian Himalaya, particularly on the Mandi to Leh transect. He has directed or supervised eight doctoral theses distributed along this transect. One of the mottos of Albrecht was that any good geological work always starts with a sound geological mapping. Whether in the Alps or in the Himalaya, Albrecht’s work excels by the quality of his geological maps. It is becoming a hallmark of Albrecht’s work. Indeed, the numerous field missions he led or supervised in Lahul, Zanskar and Ladakh regions allowed the achievement of detailed geological maps covering a remarkable large area of the NW Indian Himalaya.
The research of Albrecht Steck is characterized by the combination of field observations (mapping, stratigraphy, structures and metamorphism) in order to decipher the geometry, kinematics and tectono-metamorphic history associated with orogenic processes. His scientific approach combining a variety of field, structural, petrographic and analytical methods is a hallmark of Albrecht’s research. Two publications reflect particularly well the research works led by Albrecht Steck. The first (Steck et al. 1993) concerns a transect from the High Himalayan Crystalline of Lahul to the south to the Indus suture zone to the north; the second (Steck et al. 1998) focused on a complete geological transect through the Tethys Himalaya and the Tso Morari area. The results of these expeditions are also synthesized in a general publication of the Geology of NW Himalaya (Steck 2003). For Albrecht Steck, geology must be made in the field and out of the main touristic roads. His long-term commitment to the detailed study of the NW part of the Himalaya of India significantly contributed to a better understanding of the geology of this region. With Albrecht Steck, the Alpine and Himalayan geological community has lost an eminent researcher and a true Nature lover.
Albrecht Steck has contributed to many geological maps and articles published in peer-reviewed journals. Here are three of his major contributions:
Steck, A. (2003). Geology of the NW Indian Himalaya. Eclogae Geologicae Helvetiae, 96, 147–196.
Steck, A., Spring. L., Vannay, J.-C., Masson, H., Stutz, E., Bucher, H., Marchant, R., Tièche, J.-C. (1993). Geological transect across the Northwestern Himalaya in eastern Ladakh and Lahul (A model for the continental collision of India and Asia). Eclogae Geologicae Helvetiae, 86(1), 219–263.
Steck, A., Epard, J.-L., Vannay, J.-C., Hunziker, J., Girard, M., Morard, A., Robyr, M. (1998). Geological transect across the Tso Morari and Spiti areas: The nappe structures of the Tethys Himalaya. Eclogae Geologicae Helvetiae, 91, 103–121.
Foreword
Rodolphe CATTIN1 and Jean-Luc EPARD2
1University of Montpellier, France
2University of Lausanne, Switzerland
The Himalaya is well known as the largest and highest mountain belt on Earth, stretching 2,500 km from the Nanga Parbat syntaxis in the northwest to the Namche Barwa syntaxis in the southeast, with peaks exceeding 8,000 m in altitude. Resulted from the ongoing collision between the India and Asia plates, the Himalaya is frequently used as the type example of a largely cylindrical mountain belt with a remarkable lateral continuity of major faults and tectonic units across strike.
Advances in geoscience over the past few decades have revealed a more complex picture for the dynamic of this giant, with open questions about the initial stages of the Himalayan building, lateral variations in its structures, variations in tectonic forcing, tectonic–climate coupling and assessment of the natural hazards affecting this area.
In this book, we present the current knowledge on the building and present-day behavior of the Himalayan range. The objective is not to be exhaustive, but to give some key elements to better understand the dynamics of this orogenic wedge. The three volumes of this book present (1) the geodynamic framework of the Himalayan range, (2) its main tectonic units and (3) its current activity. The chapters and volumes in this book are self-contained and can be read in any order. However, the three volumes are linked and provide together a self-consistent image of the Himalayan dynamic at various temporal and spatial scales.
Volume 1, entitled Geodynamic Setting of the Himalayan Range, addresses the tectonic framework of the Himalaya and Tibet, the segmented nature of the Himalayan belt and gives two examples of studies focused on near-surface active fault imagery in Bhutan, and hydrothermal system in Nepal.
This volume is coordinated by Rodolphe Cattin (University of Montpellier, France) and Jean-Luc Epard (University of Lausanne, Switzerland) with the help of the editorial team composed of Laurent Bollinger (French Alternative Energies and Atomic Energy Commission, France), György Hetényi (University of Lausanne, Switzerland), Vincent Godard (University of Aix-Marseille, France), Martin Robyr (University of Lausanne, Switzerland) and Julia de Sigoyer (University of Grenoble, France).
All royalties allocated to the authors of this book will be donated to the “Seismology at School” program (see the next pages).
PrefaceFrom Research to Education: The Example of the Seismology at School in Nepal Program
György HETÉNYI1 and Shiba SUBEDI1,2
1Institute of Earth Sciences, University of Lausanne, Switzerland
2Seismology at School in Nepal, Pokhara, Nepal
Scientific research aims at observing and understanding processes, and enriching our knowledge. But who is in charge of transferring this knowledge to society, to everyday life? Can we expect any researcher to become a company CEO, an engineer, a policy maker or a teacher? Our answer is no, not necessarily, but efforts can be made in that direction, and there are successful examples.
In the context of Himalayan geoscience research, a tremendous amount of information exists. It cannot be all simplified and all translated to local languages of the Himalaya; nevertheless, we found it essential that such knowledge transfer starts. In the aftermath of the 2015 magnitude 7.8 Gorkha earthquake, through a series of fortunate steps, we found ourselves putting down one of the bricks of knowledge transfer by initiating the Seismology at School in Nepal program. Our primary pathway choice was education: in the short-term, raising earthquake awareness and better preparedness can spread through the students to their families, relatives and acquaintanceship; in the longer-term, it is today’s school students who will build the next generation of infrastructures.
The program started following a bottom-up approach, with direct cooperation with local schools in Nepal. This ensured motivated participants and direct feedback on the activities and about the needs. The program stands on two main pillars and is described in detail in Subedi et al. (2020a). First, earthquake-related topics have been synthesized and translated to Nepali, together with a series of hands-on experiments, and the local teachers have been trained so that they can teach these in their classes. Second, we have installed relatively cheap seismometers (RaspberryShake 1D) in local schools, which became part of the classroom activities and also recorded waves from earthquakes. This has sparked interest in schools, and the openly and publicly available waveform data is useful for monitoring and research as well. To more closely link these two, we have written a simple earthquake location tutorial that is feasible with typical school computers in Nepal (Subedi et al. 2021).
The program has started in Nepal in 2018; as of 2019, more than 20 schools and seismometers have been involved in the program, and the number is reaching 40 in 2022. There is measurable improvement in students’ knowledge (Subedi et al. 2020b), and the feedbacks are very positive. Parallel to classical educational pathways, a series of other activities have been developed in the Seismology at School in Nepal program. Each school has received an Emergency Meeting Point sign in Nepali language. Over 6,000 stickers reminding about earthquakes have been distributed to increase awareness (see Figure 8.10 in Volume 3 – Chapter 8). An Earthquake Awareness Song has been written and composed, and became popular on YouTube (https://www.youtube.com/watch?v=ymE-lrAK0TI). We studied the Hindu religious representation and traditional beliefs about earthquakes (Subedi and Hetényi 2021). Recently, we have developed an educational card game to improve the practical preparation and reaction to earthquakes. Finally, we maintain a website with all information openly available (http://www.seismoschoolnp.org).
The program has so far run on funding that is considered to be small in the research domain, and this has covered the cost of materials and the work in Nepal. More recently, a crowd-funding campaign has been started and evolved successfully – we are very grateful to all funders and donators! In the future, the program aims at growing further, all across Nepal and hopefully all along the Himalaya. This will require more manpower and more funds. The authors of this book have generously given their consent to transfer all royalties to the Seismology at School in Nepal program thank you very much!
There is a strong similarity between this book and the Seismology at School in Nepal program: they both aim at taking research results and carrying them to non-specialists. This book is planned to be published in several languages, and to reach students and interested people around the world. The educational program in Nepal aims at bringing earthquake knowledge to those who really need it as they live in a high hazard area. Both efforts aim at increasing awareness, and, thereby, we hope and wish that their effects reach further across all society.
October 2022
References
Subedi, S. and Hetényi, G. (2021). The representation of earthquakes in Hindu religion: A literature review to improve educational communications in Nepal.
Front Commun
, 6, 668086. doi:10.3389/fcomm.2021.668086.
Subedi, S., Hetényi, G., Denton, P., Sauron, A. (2020a). Seismology at school in Nepal: A program for educational and citizen seismology through a low-cost seismic network.
Front Earth Sci
, 8, 73. doi:10.3389/feart.2020.00073.
Subedi, S., Hetényi, G., Shackleton, R. (2020b). Impact of an educational program on earthquake awareness and preparedness in Nepal.
Geosci Commun
, 3, 279–290. doi:10.5194/gc-3-279-2020.
Subedi, S., Denton, P., Michailos, K., Hetényi, G. (2021). Making seismology accessible to the public in Nepal: An earthquake location tutorial for education purposes.
Bull Nep Geol Soc
, 38, 149–162.
PART 1Tectonic Framework of the Himalaya and Tibet
1Plate Reconstructions and Mantle Dynamics Leading to the India–Asia Collision
Gweltaz MAHÉO1 and Guillaume DUPONT–NIVET2
1Laboratoire de Géologie : Terre, Planètes et Environnement, Claude Bernard University, Lyon, France
2Géosciences Rennes, University of Rennes, France
1.1. Introduction
The origin of the Himalayan range and Tibetan Plateau, the highest morphological feature of the Earth, has always been highly debated. Following the early thermal contraction models of the 19th century, Argand (1924) was the first to suggest that the Himalaya and Tibetan Plateau orogenesis resulted from the convergence of the Indian and Eurasian continents: le jeu dominant, c’est le rapprochement de deux serres continentales, l’Indo-Afrique et la vieille Eurasie, avec rétrécissement de la Téthys1. In this early view, India (with Africa) and Eurasia continents (named Sial) are moving on a “Sima” basement (previous name of the mantle) and separated on oceanic basin the Tethys (Figure 1.1). This view was applied by Wegener (1929) in his famous continental drift model. Wegener also recognized the long journey of India across the Tethys Ocean. Based on evidence of Carboniferous glaciation on the Indian continent, and the lack of such features in Asia, he assumed that India used to be located close to the South Pole while Asia was in the northern hemisphere. Most ensuing models then related the Himalayan building with the shortening of the Tethyan “geosyncline” during the northward migration of the Indian continent across the Tethys Ocean, and recognized the remains of these oceanic domains in the rocks constituting the “Tethyan Himalaya Unit”(Gansser 1964; Holmes 1965, see Volume 2 – Chapter 3)
Figure 1.1.Gondwana configuration before the Atlantic Ocean opening. Redrawn after Argand (1924)
Then came the plate tectonic model revolution conceptualized by Holmes (1965), initiated by Hess (1962), observations of marine magnetic anomalies and their interpretation to infer tectonic plate motion by Vine and Matthews (1963). Dewey and Bird (1970) proposed that the Tethyan basin was actually made of oceanic crust, recognized oceanic rocks in the Himalaya as remnants of oceanic crust (later called ophiolites) trapped in suture zones between colliding continental plates following closure of the “Neotethys Ocean” (see Volume 2 – Chapter 2).
The first paleogeographic reconstruction of India’s northward migration across the Neotethys includes early paleomagnetic results and the development of the global tectonic plate circuits based on marine magnetic anomalies (see section 1.2.1 for methodology; Pozzi et al. 1982; Patriat and Achache 1984; Molnar and Tapponnier 1995). These reconstructions allowed estimating throughout geological history, the rate and direction of the Indian lithosphere displacement with respect to Eurasia (Figure 1.2). A slowdown of India–Asia convergent around 50 Ma was readily interpreted as the timing of continental collision (Figure 1.2; Patriat and Achache 1984).
Figure 1.2.Examples of the spreading rate and direction of the Central Indian Ridge (India–Africa) reconstructions based on marine magnetic anomalies data. For a color version of this figure, see www.iste.co.uk/cattin/himalaya1.zip
Since this pioneering work, the development of geophysical techniques and the accumulation of geological data has led to refinements in kinematic plate reconstructions and continental deformation allowing for precise models of the paleogeographic evolution and involved geodynamic processes.
In this chapter, we will review current data and models proposed for the India–Asia convergence history, including the age of the continental collision and the geodynamic configuration.
1.2. The India–Asia convergence and the age of the collision
1.2.1. The India–Asia convergence
The relative motions of tectonic plates are estimated through time using plate kinematic reconstructions built on the basis of “Euler poles” determined from “marine magnetic anomalies” globally defining a “plate circuit” (Hellinger 1981; Cox and Hart 1986; Torsvik et al. 2012; Müller et al. 2016). Interestingly, in the case of India and Eurasia since 120 Ma, the relative motion cannot be directly measured by marine magnetic anomalies because the oceanic lithosphere of the Neotethys between these plates has been consumed at subduction zones. The convergence is thus estimated indirectly through the plate circuit from India to Africa to South America to North America to Eurasia. Uncertainties thus accumulate and, for example, there are issues in determining the Indian–African kinematics because of the non-rigidity of the eastern African plate separating with the Nubian plate (e.g. Royer et al. 2006). However, uncertainties on the relative positions between India and Eurasia remain relatively low, within a few hundred kilometers depending on how well the corresponding Euler pole is defined and on the age of the geomagnetic reversal defining the marine magnetic anomalies (Capitanio et al. 2010).
The results show that India and Asia have been converging at high rates since 120 Ma with a sharp decrease at approximately 50 Ma that has been originally attributed to the onset of the India–Asia continental collision (Figure 1.2; Patriat and Achache 1984). Note that after 50 Ma, the relative convergence until today amounts to ca. 4,000 km. This implies that, if 50 Ma is indeed the age of the continental collision, this amount of the Indian and Asian continental lithosphere has disappeared in processes such as compressive deformation, continental subduction and lithospheric extrusion and detachment as will be discussed further below. Therefore, kinematic models are constantly being improved to quantify in detail the India–Asia convergence in order to further infer geodynamic processes involved in the continental collision (e.g. Copley et al. 2011; Capitanio et al. 2015; Webb et al. 2017; Schellart et al. 2019). Notably, sharp variations in the convergence have been interpreted to relate to more complex collision models discussed further below (Van Hinsbergen et al. 2012; Jagoutz et al. 2015; Pusok and Stegman 2020, see section 1.4.3 for discussion)). Also, convergence variations have been related to deep processes such as plumes (van Hinsbergen et al. 2011a) or slab break-off (Mahéo et al. 2009), to the nature of ocean floor sediments facilitating subduction (Behr and Becker 2018) or to thickening of the Asian lithosphere hindering subduction (Molnar and Stock 2009). In addition, changes in the convergence direction implying a rotation of India with respect to Asia (Figure 1.2) have been interpreted as resulting from the diachronous collision starting in the West and finishing in the East (e.g. Klootwijk et al. 1992; Patzelt et al. 1996; Hu et al. 2016). Other potential origins include progressive West to East tearing of the subducting Neotethys slab, breaking off the India plate following the continental plate collision (Replumaz et al. 2010) or to surface processes such as monsoons along the Himalayan front (Iaffaldano et al. 2011; Husson et al. 2014).
1.2.2. The age of the India–Asia collision
When India collided with Asia has been highly debated in the last decade and remains a major controversy. First of all, the collision age must be defined because the collision involves many processes that may be taking place at different times. The collision age considered here is the time at which the converging continental plates come into contact. This initial contact is potentially associated with the cessation of marine deposition, ophiolite obduction, continental subduction and crustal deformation of the underthrusting plate. The processes leave traces in the rocks that can help decipher their precise chronology of what happened during the collision. In the Indo–Asia convergent zone, the collision has been originally assumed to have occurred along the Indus–Yarlung suture zone (Allègre et al. 1984). This suture zone is characterized by remnants of oceanic lithosphere between the India and the Asian plates. It now separates the Lhasa terrane (the southernmost terrane of Asia, or “Greater Asia”) from the Tethyan Himalaya sediments that are generally interpreted to represent the northern passive margin of India, or “Greater India” (e.g. Figure 1.3).
Figure 1.3.India–Asia collision. The yellow parts of the continents are precisely constrained with the global plate circuit based on marine magnetic anomalies (see the text). The past continental extents are constrained by paleolatitude estimates from paleomagnetic data recovered from rocks of the “Greater India” and “Greater Asia” fragments (black and white dots respectively; modified from Dupont-Nivet et al. 2010). The gray shading indicates a continuous seismic tomography positive anomaly in the mantle, interpreted as the remnant of the subducted lithospheric slab of the Neotethys, that would have broken off at the time and location of the collision (see the text). For a color version of this figure, see www.iste.co.uk/cattin/himalaya1.zip
Various methods are used to constrain the timing of India–Asia contact (see DeCelles et al. (2014), Hu et al. (2016), Kapp and DeCelles (2019) for detailed reviews).
1.2.2.1. Decrease in India–Asia convergence rates
As previously discussed, reconstructions of the Indian plate kinematics based on paleomagnetic data indicate significant variation of the convergent rates with Asia. The evidence of a sharp decrease in the convergent rate at about 55–50 Ma was originally attributed to the collision with the onset of subduction of the Indian Continental margin beneath the Asia plate slowing down the convergence (Figure 1.2; Patriat and Achache 1984). However, deceleration of convergent rates may also be related to other features such as interaction with the Deccan Plume (van Hinsbergen et al. 2011a) or breakoff of the Neotethys oceanic lithosphere which was driving the continental subduction (Mahéo et al. 2009) as discussed above.
1.2.2.2. Reconstruction of relative plate positions
Another way to estimate the timing of collision based on paleomagnetism is to reconstruct in time the past latitudinal positions of rocks preserved in the collision zone that formed on the northern margin of Indian and on the southern margin of Asia before and during the collision (Figure 1.3; see the paleomagnetic methods in detail in 1.3.1). The age at which both paleolatitude start to overlap is thus interpreted as the age and paleolatitude of collision. This powerful approach enables us to position past continental slivers involved in the collision, but by itself it cannot resolve if these slivers were really at the end of Indian and Asian promontories or if they were separated from these continents by large oceans.
1.2.2.3. Provenance of detrital sediments
As the continent margins of India and Asia are coming into contact, detrital sediments may travel across the future suture zone. The provenance of detrital material usually bears characteristic features that enable us to distinguish its source continent, based on mineralogy, coupled with mineral (especially zircon) geochemical composition and ages (e.g. Critelli and Garzanti 1994; DeCelles et al. 1998). The most recent estimates based on detrital evidence of Asian detritus onto the India passive margin as it arrived in the collision zone pinpoint the collision age precisely ca. 58–60 Ma (e.g. DeCelles et al. 2014; Hu et al. 2016; Najman et al. 2017; Garzanti et al. 2018; Garzanti 2019). However, although the age is well constrained, the source of some detrital sediments is highly debated because its Asian provenance, characterized by distinct signatures from the Yarlung Zangpo suture, may be ambiguous. Indeed, several authors suggest that some of these distinctively Asian sediments may actually be sourced from intraoceanic units, such as the Kohistan–Ladakh arc. The latter came into collision first with India coming northward at about 55–60 Ma and only later with Asia at about 40–50 Ma (Bouilhol et al. 2013; Jagoutz et al. 2015; Bhattacharya et al. 2020; Martin et al. 2020). Such interpretation has strong incidences on plate reconstructions that will be discussed in the following section.
1.2.2.4. Paleontological records
Records use Indian fossil first occurrences in Asia to evidence potential land connections for biotic interchange between Asia and India (e.g. Jaeger et al. 1989; Ali and Aitchison 2008). However, changes in landmass connection related to the sea-level change as well as plate tectonic may have induced more complex biological interactions than previously thought (Chatterjee and Scotese 2010). More recently, these results have been combined with statistical analyses of molecular phylogenies showing that interchange can significantly pre- or post-date the collision time depending on various taxon transports and the occurrence of inter-continental weepstake dispersals through rafting (e.g. Krause et al. 2019). In fine, the estimates are relatively imprecise and more relevant to document the impact of the collision on biotic evolution than the opposite.
1.2.2.5. Continental subduction
Following collision, the Indian north continental margin is temporally subducted beneath India as a consequence of the subducting Neotethys ocean slab drag, taking rocks to great depths where minerals are formed and transformed at so-called ultrahigh pressures (UHP). Some of these rocks are later exhumed and can be collected today in the collision zone. Then, the timing of the UHP Indian continental rock formation can be dated with the associated thermochronological systems and these ages will provide an upper bond for the onset of collision. Such rocks are only preserved in western Himalaya, as other high-pressure rocks from central Himalaya are relicts partially retromorphosed in granulite facies conditions during collision that has obliterated most of the UHP minerals (see Guillot et al. (2008), and Volume 2 – Chapter 4 for details). The ages of the UHP metamorphism range from 53 to 46 Ma, thus imply that continental subduction of the north Indian margin was already ongoing at that time in western Himalaya and thus that continental collision had already occurred. Note that this timing is consistent with the slowdown of the India convergence rate that was indeed attributed to continental subduction. However, the question remains if this metamorphism is recording the subduction of India beneath Asia or beneath some intraoceanic arc.
1.2.2.6. Magmatism (cessation and onset)
Magmatic pulses and associated sources generated by the subduction of various materials during the convergence and collision may also help reconstruct the geodynamic evolution and in turn constrain the timing of collision. The closure of the Neotethys Ocean by subduction is related to several magmatic episodes, especially the emplacement of the Gangdese or Transhimalaya arc along the south Asian active continental margin (Allègre et al. 1984; Kapp and DeCelles 2019). However, the magmatic evolution of the Gandese arc is relatively complex with arc-like magmatic rocks emplaced from Paleocene to Miocene time (e.g. Chung et al. (2005), Zhu et al. (2015), Ma et al. (2022), for review). Actually, several processes may explain this magmatism including oceanic and continental subduction, slab breakoff, roll-back or delamination. Using the magmatism to constrain the transition from oceanic to continental collision is thus complex and led to various collision estimates ranging from 40 Ma to 60 Ma (see Hu et al. (2016), for detailed review).
1.2.2.7. Sedimentary evolution
Contact between previously separated continents and ongoing crustal deformation will have significant impact on sedimentary evolution and basin dynamics. Sediment records related to collision include cessation of oceanic sedimentation, change in basin dynamic recorded by major unconformities as well as the developement of a foreland basin on the India continent or detrital sedimentation on the suture zone. These sedimentary records may postdate collision, but some, such as cessation of marine sedimentation, may occur several million years after collision depending on sea level changes. One of the most convincing and well-constrained sedimentary records of the collision is the developement and evolution of a foreland basin related to Indian plate flexuration following continental subduction as well as ophiolite obduction (Garzanti et al. 1987; Beck et al. 1996; DeCelles et al. 2002). Detailed stratigraphic studies in the western Himalaya (e.g. Garzanti et al. 1987; Guillot et al. 2003) evidence sedimentation change at about 55 Ma related to flexuration of the Indian Continental margin beneath the obduction Neotethys ophiolite. This implies that Indian continental subduction was already ongoing at about 55 Ma as suggested by UHP rock age as well as convergent rate decrease and thus place collision before 55 Ma. Similarly, stratigraphic data from the westernmost Himalaya (Beck et al. 1996; Rowley 1996) evidence that collision occurred as early as late Cretaceous, leading to the suggestion of a West to East diachronous collision, as confirmed by the more recent stratigraphic compilations along the Himalaya (Hu et al. 2016).
1.2.2.8. Crustal deformation
During the collision, the Indian continental crust underthrusted beneath the Asia margin (or beneath an intraoceanic arc) records significant deformation that can be quantified and dated. Especially south verging deformation (top to the south thrusting and recumbent folding) within the Indian continental margin sedimentary cover, the Tehyan Himalaya is expected. The oldest of such shortening-related structures and contemporaneous metamorphism are comprised between 44 and 54 Ma (seeHu et al. (2016), for review). 66 to 55 Ma accretionnay-wegde structures have also been recognized in the Tethyan Himalaya sediments from northwestern Pakistan (Beck et al. 1995). Once again, potential arc-continent collision may also account for such features.
In summary, several methods suggest that India–Asia collision occurred at about 60–55 Ma. However, earliest (65 Ma) and latest (40 Ma) timings were also proposed. The convergence between India and Asia has been originally mostly viewed as a simple convergence associated with a unique subduction zone. However, as already suggested above, more complex settings have been proposed in approximately the last 15 years. Notably the Aitchison et al. (2007) seminal study involving possible intraoceanic subduction zones and a related intraoceanic arc that may have come into collision with the Indian continent as it was arriving from the south. In that view, India would then continue to move pushing northward the intraoceanic arc at its front until reaching the southern margin of the Asian continent. These ideas have led to a resurgence of models, data and controversies to better reconstruct the India–Asia collision. Crucial to testing these various models are the aforementioned methods to reconstruct the chronology of events associated with the collision and the position and shape of the Indian and Asian continents before collision. We now review the plate configuration models in the following two sections and discuss their implications on the current debate on the evolution of the India–Asia collision.
TO GO FURTHER ON PALEOMAGNETISM.
The tectonic plate circuit, based on retro-fitting marine magnetic anomalies of the same age, enables us to constrain only provides the motion of large tectonic plates relative to each other. However, the position through time of the plate circuit with respect to the Earth’s axis still needs to be defined. On geologic time scales, the geographic north it is indistinguishable from the position of the Earth’s magnetic pole which can be determined with paleomagnetic data properly acquired (Butler 1992). Because of tectonic plates moving, the resulting paleomagnetic poles appear to move through geologic time on a path called the apparent polar wander path (APWP). Using the plate circuit, the paleomagnetic data from all tectonic plates can be rotated into a synthetic global APWP (Besse and Courtillot 2002; Torsvik et al. 2012). This enables us to combine paleomagnetic datasets from all plates and reduce uncertainties on the position of the plate circuit with respect to the Earth’s axis. An alternative method consists of using the position of plates with respect to hotspot tracks (e.g. Müller et al. 2018). But hotspots in the mantle move with respect to the Earth’s axis and still require to be referenced using paleomagnetic data from hotspots.
The plate circuit and associated global APWP are particularly important to place quantitative constraints on amounts and rates of shortening accommodated in the Himalaya–Tibetan orogen, as well as to identify ages of the India–Asia collision. These arguments eventually lie at the basis of spectacular geodynamic and tectonic processes, such as tectonic extrusion, the possibility of many hundreds of kilometers of continental subduction, and consumption of well over 1,000 km of a continental overriding plate during ocean closure and continent–continent collision. However, the synthetic APWP remains based on too limited low amounts of data. As a result, sliding windows of 10, 20 or even 50 Ma are used, filtering out “details” in plate motions. Recent efforts have identified issues in the statistical methods estimating uncertainties on the APWP and are actively working on developing new methods incorporating various datasets to reduce APWP uncertainties and ultimately better define the India–Asia convergence evolution (Rowley 2019; van Hinsbergen et al. 2021; Vaes et al. 2022).
