Regional Geology Reviews

Series editors Roland Oberhänsli Maarten J. de Wit François M. Roure

For further volumes: http://www.springer.com/series/8643 View of Mt Nilgiri from Tatopani Megh Raj Dhital

Geology of the Himalaya

Regional Perspective of the Classic Collided Orogen

123 Megh Raj Dhital Central Department of Geology Tribhuvan University Kirtipur, Kathmandu Nepal

ISBN 978-3-319-02495-0 ISBN 978-3-319-02496-7 (eBook) DOI 10.1007/978-3-319-02496-7 Springer Cham Heidelberg New York Dordrecht London

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Cover illustration: Photo by Megh Raj Dhital South face of Mt Nilgiri, viewed from Tatopani.

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Springer is part of Springer Science+Business Media (www.springer.com) This book is dedicated to the memory of Toni Hagen Foreword

Perhaps no sector in the Himalaya is endowed with so exciting a geological setup as Nepal. Forming a bridge between the Western and Eastern Himalaya, Nepal occupies a pivotal and significant place in the geology of the Himalaya. Stretching from the low lying foothill in south to the highest peak of Sagarmatha (Mt. Everest) in the north and covering a vast time span from the to Holocene, the Nepal Himalaya preserves unique geological events. Varied kinds of igneous rocks, metamorphosed sequences and sedimentary rocks of disparate environments make a captivating geological mosaic. Yet this fascinating terrain did not receive the attention of geologists as it deserved. The early contributions were restricted to isolated sectors, leaving many gaps in the understanding of the geology of Nepal. It is thus fitting that these gaps are being filled by Prof. Megh Raj Dhital—son of the soil, in this book. I have been in touch with him for quite some time and have held several discussions. He has painstakingly compiled the data scattered in numerous publications and arranged these into several chapters with informative maps, charts and figures with his own inputs. To begin, the reader is introduced to the role of plate in the creation of the Himalaya. The most fascinating aspect of the Himalaya to one and all is its charming scenery; naturally the physiographic subdivisions have to be dealt in a book on geology as the topography is controlled by the rocks. Political boundaries were created much after the Himalaya came into existence; the geological elements of Nepal, therefore, should find continuity in the adjoining Western and Southeast Himalaya and the Peninsular . An elaboration of this aspect forms a basis for regional understanding of the geology of the Himalaya. The geology of the Lesser Himalaya constituted of unfossiliferous rocks that have been tectonically disrupted is nightmare to any stratigrapher; seven chapters are devoted to their exhaustive account. Elaboration of complicated geology of the Higher Himalaya and the enigma of inverted grade of in the Himalaya is of interest to one and all. Richly fossiliferous rocks of the Tethyan Himalaya evoke curiosity even amongst layman and no book on geology of Nepal could be complete without their description. Siwalik rocks, rep- resenting almost the final phase of the mountain building, find copious place. The and intermontane basins are unique to the Nepal Himalaya; their genesis makes an interesting reading. Neotectonics having environmental significance should be a must to the planners and administrators. The plethora of information of 36 chapters has been summarised with con- clusions in the final chapter. One may differ with Prof. Dhital’s conclusions, but the narrative is exhaustive and makes an absorbing reading. He has succeeded in his task and discharged the debt he owes to the Nepal geology. This book completes the panorama of the Himalayan geology stretching from the West to the East.

Panchkula O. N. Bhargava

vii Preface

With the exception of the work carried out by a handful of early explorers, intensive geo- logical investigations in Nepal began only in 1951, exactly 100 years after the establishment of the Geological Survey of India. But, soon after, the geological literature on Nepal began to grow exponentially, and presently the number of publications has become too numerous, and the information is scattered worldwide through various books, periodicals, and unpublished reports in more than seven languages. Therefore, it is desirable to gather, amidst many details, the important geological knowledge of the Nepal Himalaya and to go through the prevailing concepts, behind the formation and development of this towering mountain range of the world. This book has ensued from my research into the existing geological literature as well as its developmental trend in the Himalaya. While preparing the book, I have also drawn on my own geological investigations over the length and breadth of Nepal as well as its surrounding regions. Consequently, I felt it necessary to preface this book also with a few words on the epistemic aspect of geological research in the Himalaya. Geological investigation in the Himalaya, not unlike in any other part of the earth’s crust, has to deal primarily with infor- mation gathering, based on some conceptual connotations. Indeed, to trace even a simple geological contact, some theoretical background is necessary. However, one of the distinctive attributes of Himalayan geology is the proliferation of views on various geological phe- nomena, operating in this majestic mountain realm. The geological literature of the Himalaya is beset with the origin, evolution, and demise of such diverse concepts and ideas. At first glance, the geological literature of the Himalaya may seem to be overwhelmed with such conundrums or contradictions and the science of geology in a state of disorder. However, a deeper insight into the subject matter may bring out an order out of the chaos. These theo- retical discourses were so vital that they provided ample impetus to carry out intensive research in this classic collided orogen. As a result, albeit gradually, a clearer and more beautiful geological picture of the whole Himalayan Range has come into sight. The centrally located Nepal Himalaya is expediently circumstanced for the study of Himalayan geology with its diverse dimensions. It is in the Nepal Himalaya, where most theories and concepts have flourished in the past 60 years of time. Though it is a relatively short interval, if we take into account the last 200 years of intense and exhaustive investigation of the Himalaya by a gamut of researchers from various countries of the world, the outcomes have proved to be astonishingly fruitful in their application to the whole Himalayan Range and also beyond its borders. Geologists do not spend whole of their life in theoretical discourses alone, but they do produce a range of geological maps, immensely useful to the governmental as well as private organisations in their endeavour to develop construction material- or mineral-based industries, hydropower projects, or road networks, to extract groundwater, and ameliorate land with irrigation facilities. Such scrupulously drawn maps are also inevitable for petroleum explo- ration, urban planning, natural hazards assessment, and environmental protection. Therefore, many detailed geological maps of some particular areas are included in this book. Since more than two-thirds of the total area of Nepal is hitherto unmapped on a large scale, there remains much research work to be carried out in the future. In fact, one of the root causes of many

ix x Preface contradictory opinions on various geological processes is the state of poor geological map- ping. Ironically, some earlier maps portray the field reality more accurately and vividly than those heavily laden with specific theoretical conjectures. It is endeavoured to bring together, through this book, the geology of the whole Himalayan Range of Nepal, i.e., from the graceful grasslands of the Ganga basin on the south to the towering Tethyan zone on the north. Though many writers have chosen to discuss the geology of the Himalaya from south to north, this book is arranged somewhat differently. It is because, the limits of various broad geological divisions are not always distinct, and it is desirable to follow the geological convention of dealing with the oldest units first. Hence, after giving introduction to the Himalaya and neighboring regions, the book describes the oldest sequence of the Lesser Himalaya, and it is followed by the Higher Himalaya, Tethys Himalaya, Siwaliks, and the youngest Terai and intermontane basins. It is my belief that without a comprehensive look at the various Himalayan terranes, it is practically impossible to grasp fully the process, operating behind the formation and devel- opment of the spectacular Himalaya. However, it is not intended merely to document all the scientific ontology, but an attempt is made to reveal a sound basis to the prevailing concepts. It is anticipated that the book will help the reader to move forward from a cognitive approach to a constructive one with the praxis of linking a variety of knowledge, including the earlier inferences or views and contemporary theories or models, where the intent of both the past and present researchers is more or less the same, but their investigation process can be different.

Kathmandu, July 2014 Megh Raj Dhital Acknowledgments

Tribhuvan University generously granted me a year-long sabbatical leave to carry out this research. The Central Department of Geology, Tribhuvan University, not only provided me with library and laboratory facilities, but also supported my fieldwork in various parts of Nepal. The University of Natural Resources and Applied Life Sciences (BOKU), the Uni- versity of Vienna, and the Geological Survey of Austria offered library and laboratory facil- ities. Information was also gathered from Tübingen University and ETH Zürich libraries. I also received a 4-month-long research fellowship from Hokkaido University. Nepal Academy of Science and Technology as well as Indian National Science Academy facilitated my 3-month- long research in Kolkata. The library of the Geological Survey of India, as well as the Presidency University, Kolkata, and Tongji University, Shanghai, were inevitable for gath- ering much needed information. Maps, data and reports were also acquired from the Department of Mines and Geology, the Department of Survey, and the Department of Irrigation, Kathmandu, Nepal. International Centre for Integrated Mountain Development (ICIMOD) assisted me with GIS and related tools. It would have been impossible to write this book without an enormous amount of technical as well as intellectual help from my seniors, colleagues, friends and students. I thank all of them, and especially the following individuals for their cooperation: Madhav Prasad Sharma, Ramesh Prasad Bashyal, Toran Sharma, Bishal Nath Upreti, Dibya Ratna Kansakar, Krishna Prasad Kaphle, Prakash Chandra Adhikary, Sarbjit Prasad Mahato, Vishnu Dangol, Ram Bahadur Sah, Pradeep Kumar Mool, Samjwal Ratna Bajracharya, Suresh Das Shrestha, Madhav Belbase, Ananta Prasad Gajurel, Dinesh Pathak, Lila Nath Rimal, Lalu Prasad Paudel, Khum Narayan Paudayal, Naresh Kazi Tamrakar, Subas Chandra Sunuwar, Soma Nath Sapkota, Sudhir Rajaure, Rajendra Prasad Khanal, Prem Bahadur Thapa, Kamal Raj Regmi, Ranjan Kumar Dahal, Subesh Ghimire, Motilal Ghimire, Kamala Kant Acharya, Sunil Dwivedi, Basanta Raj Adhikari, Prabin Kayastha, Amardeep Regmi and Gautam Khanal. Jean Friedrich Schneider kindly invited me to research for 9 months at BOKU. Hermann Häusler allocated space and computer facilities, whereas Bernhard Grasemann granted per- mission to library and equipment access at Vienna University. Thomas Hofmann from the Geological Survey of Austria made available various books and journals as well as published and unpublished reports. Many stimulating and fruitful discussions with Gerhard Fuchs and Wolfgang Frank clarified several issues related to tectonics and . Hisao Ando, Kazunori Arita, Erwin Appel, Yuichiro Tanioka, Florimond De Smedt, Bai Yun, Pitambar Gautam and Sumit Kumar Ray helped substantially in my research endeavour. I am indebted to Om Narain Bhargava for critically reviewing the manuscript and making painstaking corrections as well as for giving many practical suggestions. He also facilitated my field observations in Solan and Simla.

xi xii Acknowledgments

I am grateful to all the authors and publishers, who kindly gave permission to use their material. I thank the staff of Springer for their enthusiastic and unfailing help throughout the production of this book, and particularly Dörthe Mennecke-Bühler and Ashok Arumairaj for editorial advice, guidance and speedy correction. Errors of commission and omission are my own. Last but not least, I am grateful to my wife and children for their understanding and encouragement. Megh Raj Dhital Contents

1 Introduction ...... 1 1.1 Early Investigations...... 1 1.2 Classification Schemes ...... 4 1.3 Proposed Subdivisions...... 6 References...... 9

Part I Geological Setting and Physiography

2 Geological Setting of Himalaya ...... 13 2.1 Tibetan Plateau...... 13 2.2 Indus–Tsangpo Zone ...... 15 2.3 Himalayan Orogen ...... 15 2.4 Ganga ...... 16 2.5 Basement Structure of Ganga Basin ...... 16 2.6 Unstable River Courses ...... 19 References...... 20

3 Physiography of Nepal ...... 23 3.1 Terai ...... 23 3.1.1 Upper Terai or Bhabar Zone ...... 23 3.1.2 Middle Terai or Marshy Land ...... 23 3.1.3 Lower Terai or Gangetic Alluvium ...... 24 3.2 Siwaliks and Dun Valleys ...... 24 3.3 Mahabharat Range ...... 29 3.4 Midlands ...... 30 3.5 Fore Himalaya ...... 30 3.6 Great Himalayan Range...... 31 3.7 Inner Himalayan Valleys ...... 31 3.8 Tibetan Marginal Ranges ...... 32 References...... 32

Part II Geology of Neighboring Regions

4 Northwest Himalaya ...... 37 4.1 Medlicott’s Classification...... 37 4.1.1 Infra-Blaini or Simla ...... 37 4.1.2 Blaini Formation...... 37 4.1.3 Infra-Krol Formation ...... 38 4.1.4 Krol Formation...... 38 4.1.5 Metamorphic Equivalents of Infra-Krol and Krol Formations . . . 38 4.1.6 Subathu Formation ...... 39

xiii xiv Contents

4.1.7 Dagshai and Kasauli Formations...... 39 4.1.8 Siwaliks...... 39 4.2 Oldham’s Investigations in Jaunsar and Bawar ...... 39 4.2.1 Jaunsars and Chakrata Formation ...... 39 4.2.2 Deoban Formation ...... 40 4.2.3 Mandhali and Bawar Formations ...... 40 4.3 Proposal of in Simla Area by Pilgrim and West ...... 41 4.3.1 Thrusts and Nappes...... 41 4.3.2 Jutogh Formation ...... 41 4.3.3 Chaur Gneissose Granite ...... 41 4.3.4 Chail Formation ...... 42 4.3.5 Jagas (Jaunsar) Formation ...... 42 4.3.6 Naldera and Simla Slates ...... 43 4.3.7 Shali Limestone ...... 43 4.3.8 Opinions at Variance...... 43 4.4 Auden on the Krol Belt ...... 44 4.4.1 Simla Slates ...... 44 4.4.2 Mandhali Formation (Lower Jaunsar) ...... 45 4.4.3 Chandpur Formation (Middle Jaunsar)...... 45 4.4.4 Nagthat Formation (Upper Jaunsar) ...... 45 4.4.5 Blaini Formation...... 45 4.4.6 Infra-Krol Formation ...... 45 4.4.7 Krol ...... 45 4.4.8 Krol ...... 46 4.4.9 Tal Formation ...... 46 4.4.10 Subathu Formation ...... 46 4.4.11 Dagshai Formation ...... 47 4.4.12 Kasauli Formation...... 47 4.4.13 Lower Siwaliks (Nahans) ...... 47 4.4.14 Dolerites and Associated Rocks ...... 47 4.5 Shali : West’s Version ...... 47 4.5.1 Shali Thrust ...... 47 4.5.2 Lower Shali Limestone ...... 47 4.5.3 Shali Slates and Chail Formation ...... 47 4.5.4 Upper Shali Limestone ...... 47 4.6 Further Investigations in Simla–Krol Belt...... 47 4.6.1 Tiuni Formation ...... 48 4.6.2 Deoban Formation ...... 48 4.6.3 Simla Group ...... 48 4.6.4 Mandhali Formation ...... 49 4.7 Pre-Tertiary Outliers in the Sub-Himalaya ...... 49 4.8 Lithostratigraphic Correlation and Other Issues ...... 49 4.8.1 Correlation of Simla Slates and Allied Rocks ...... 49 4.8.2 Correlation of Blaini Boulderbeds and Other Unfossiliferous Lesser Himalayan Rocks ...... 50 4.8.3 Correlation of Carbonate Sequences ...... 50 4.8.4 Depositional Environment of Simla Slates and Allied Rocks . . . 50 4.8.5 Depositional Environment of Krol Formation and Related Rocks ...... 50 4.8.6 Subathu–Dagshai Passage-Beds ...... 50 References...... 51

5 Southeast Himalaya and Adjacent Indian Peninsula ...... 53 5.1 Gondwanas of Indian Peninsula ...... 53 5.1.1 Lower Gondwanas (?Carboniferous–Permian: 280–245 Ma) . . . . 53 Contents xv

5.1.2 Damudas (Permian)...... 54 5.1.3 Middle Gondwanas (Triassic: 245–208Ma)...... 55 5.1.4 Upper Gondwanas (Jurassic–Early Cretaceous: 208–110 Ma) . . . 55 5.2 Lesser Himalayan Sequence ...... 55 5.2.1 Daling and Shumar Groups ...... 56 5.2.2 Baxa Formation ...... 56 5.2.3 Diuri Formation ...... 56 5.2.4 Setikhola Formation (Permian) ...... 56 5.2.5 Damudas ...... 57 5.3 Higher Himalayan Crystallines ...... 57 5.3.1 Lime-Silicate Inclusions in Darjeeling ...... 58 5.3.2 Pegmatites and Basic Sills ...... 58 5.4 Inverted Metamorphism ...... 58 5.5 Proposition of a Huge Recumbent ...... 58 5.6 Folded Tethyan Rocks...... 58 5.7 Interrupted Siwalik Belt...... 59 5.8 South-Tilted Alluvial Terraces ...... 59 5.9 Frontal ...... 59 References...... 61

Part III Lesser Himalaya

6 Introduction to Lesser Himalaya ...... 65 6.1 Pioneer Investigations in Nepal...... 67 6.2 The Great Controversy ...... 67 6.3 Distribution of Lesser Himalayan Sequence ...... 68 6.3.1 Tectonic Windows ...... 68 6.3.2 Inner Zone...... 70 6.3.3 Intermediate Zone ...... 70 6.3.4 Outer Zone ...... 70 6.3.5 Older Sedimentary Slices in the Siwalik Belt ...... 70 6.4 Classifying Lesser Himalayan Rocks ...... 70 6.4.1 Augen ...... 71 6.4.2 Igneous Rocks ...... 72 6.4.3 Carbonate Sequences...... 73 6.5 Correlation of Unfossiliferous Sequences ...... 73 6.6 Gondwanas and Coal ...... 74 6.7 Inverted Metamorphism ...... 74 6.8 Structure of Inner Zone ...... 75 6.9 Structure of Intermediate Zone ...... 75 6.10 Structure of Outer Zone...... 75 6.11 Main Boundary Thrust ...... 76 References...... 78

7 Lesser Himalaya of Mahakali–Seti Region ...... 81 7.1 Carbonates and Allied Rocks in Tectonic Windows of Darchula ...... 81 7.2 Investigations Between Darchula and Budar ...... 83 7.2.1 Malikarjun Thrust and Early Strata...... 84 7.2.2 Superposed Folding in Baitadi Carbonates and Patan Formation ...... 86 7.2.3 Early Tertiary Beds of Patan–Pancheshwar...... 87 7.2.4 Budar–Gaira Transect ...... 89 References...... 90 xvi Contents

8 Lesser Himalaya of Karnali–Bheri Region ...... 93 8.1 Galwa Tectonic Window ...... 93 8.2 Surkhet–Dailekh Tract ...... 93 8.3 Fossiliferous Beds of Barikot Window...... 98 8.4 Region Between Jajarkot and Botechaur ...... 98 8.4.1 Kapurkot Thrust ...... 98 8.4.2 Sharda Group...... 98 8.4.3 Kubhinde Complex ...... 100 8.4.4 Antiformal Closure of Mokhla ...... 101 8.4.5 Dailekh Group ...... 102 8.4.6 Folds of Chhera Khola ...... 104 8.4.7 Budar Thrust Termination ...... 104 8.4.8 Frontal Imbricate Zone ...... 104 8.4.9 Daban Supergroup ...... 105 8.5 Outer Lesser Himalaya of Dang, Sallyan, and Piuthan ...... 105 8.5.1 Sharda Group...... 105 8.5.2 Correlation and Comparison of Sharda Group ...... 108 8.5.3 Gwar Group...... 111 8.5.4 Tosh Group ...... 122 References...... 124

9 Lesser Himalaya of Gandaki Region ...... 125 9.1 Inner Zone of Gorkha ...... 125 9.1.1 Kuncha Formation ...... 125 9.1.2 Garnetiferous and Gneisses ...... 125 9.1.3 Graphitic Schists and ...... 126 9.1.4 Higher Himalayan Sequence...... 127 9.1.5 Structure of Inner Zone ...... 127 9.1.6 Nepheline Syenites ...... 129 9.2 Intermediate Zone of Kusma–Syangja ...... 131 9.2.1 Kuncha Formation ...... 131 9.2.2 Naudanda ...... 131 9.2.3 Nayagaun Formation ...... 131 9.2.4 Nourpul Formation ...... 134 9.2.5 Dhading Dolomite ...... 134 9.2.6 Benighat Slates...... 134 9.2.7 Sorek Formation ...... 135 9.2.8 Dhanpure Limestone ...... 136 9.2.9 Sisne Formation ...... 136 9.2.10 Amile Formation ...... 136 9.2.11 Dumri Formation ...... 136 9.2.12 Structure of Intermediate Zone ...... 137 9.3 Outer Zone of Kali Gandaki and Palpa ...... 137 9.3.1 Heklang Formation ...... 137 9.3.2 Virkot Formation ...... 137 9.3.3 Chappani Formation ...... 140 9.3.4 Khoraidi Formation...... 141 9.3.5 Saidi Khola Formation ...... 141 9.3.6 Ramdighat Formation ...... 141 9.3.7 Kerabari Formation ...... 143 9.4 Stratigraphy of Tansen Group...... 144 9.4.1 Sisne Formation ...... 144 9.4.2 Taltung Formation ...... 147 9.4.3 Amile Formation ...... 148 9.4.4 Bhainskati Formation ...... 149 Contents xvii

9.4.5 Dumri Formation ...... 150 9.5 Structure of Outer Zone...... 151 References...... 151

10 Lesser Himalaya of Bagmati–Gosainkund Region...... 153 10.1 Intermediate Zone and Mahabharat Range ...... 153 10.1.1 Kuncha Formation ...... 153 10.1.2 Fagfog Quartzite...... 154 10.1.3 Dandagaon ...... 155 10.1.4 Nourpul Formation ...... 155 10.1.5 Dhading Dolomite ...... 157 10.1.6 Benighat Slates...... 157 10.1.7 Malekhu Limestone...... 158 10.1.8 Robang Formation (Robang Phyllites with Dunga ) ...... 158 10.1.9 Main Central Thrust ...... 158 10.2 Proterozoic Lesser Himalayan Slices in the Siwalik Belt ...... 159 10.2.1 Red-Purple Sandstone and ...... 159 10.2.2 Gray-Green Shale and Sandstone ...... 159 10.2.3 Gray Shale...... 159 10.2.4 Basic Rocks ...... 159 References...... 161

11 Lesser Himalaya of Koshi Region ...... 163 11.1 Kharidhunga Area...... 163 11.2 Namdu–Gairimudi Area...... 165 11.3 Metasediments and Mylonitic Gneisses of Phaplu ...... 168 11.4 Harkapur–Mane Bhanjyang Area ...... 168 11.5 Imbricate Slices of Katari–Bagpati Area...... 172 11.6 Kampu Ghat Area...... 173 References...... 177

12 Lesser Himalaya of Arun–Tamar Region...... 179 12.1 Arun Window ...... 179 12.2 Sabha Khola Area...... 179 12.3 Taplejung Window ...... 183 12.4 Tribeni–Dharan–Dhankuta Area ...... 185 12.5 Barahakshetra...... 187 12.6 Mechi Transect...... 191 References...... 193

Part IV Higher Himalaya

13 Introduction to Higher Himalaya...... 197 13.1 Main Central Thrust ...... 199 13.2 Higher Himalayan Crystallines ...... 199 13.3 Folded Higher Himalayan Thrust Sheet ...... 201 13.4 Root Zone ...... 201 13.5 Slip Along Main Central Thrust ...... 202 13.6 South Tibetan Detachment System ...... 203 13.7 Thin-Skinned Tectonics ...... 203 13.8 Polyphase Metamorphism ...... 203 13.9 Subduction Metamorphism and Eclogites ...... 204 13.10 Barrovian Metamorphism...... 205 xviii Contents

13.11 Inverted Metamorphism ...... 205 13.12 Cambro–Ordovician Granites and Gneisses ...... 205 13.13 Tertiary ...... 206 13.14 Other Younger Leucogranites ...... 207 References...... 207

14 Higher Himalaya of Mahakali–Seti Region ...... 213 14.1 Darchula Neighborhood ...... 213 14.1.1 Zone a...... 214 14.1.2 Zone b ...... 214 14.1.3 Zone c...... 214 14.1.4 Zone d ...... 215 14.1.5 Zone e...... 216 14.1.6 Zone f ...... 217 14.1.7 Zone g: Budhi Schists ...... 217 14.1.8 Zone h: Garbyang Formation ...... 217 14.2 Dadeldhura ...... 218 References...... 218

15 Higher Himalaya of Karnali–Bheri Region ...... 219 15.1 Crystallines Around Galwa Window ...... 219 15.2 Karnali Klippe and Underlying Sequences ...... 219 15.2.1 Metamorphic Mineral Assemblage ...... 221 15.2.2 Metamorphic Zonation ...... 221 15.2.3 Mineral Chemistry and P–T Conditions ...... 223 15.3 Crystallines South of Kanjiroba ...... 223 15.4 Jaljala Klippe ...... 223 15.4.1 Metamorphism ...... 225 References...... 225

16 Higher Himalaya of Gandaki Region...... 227 16.1 Kali Gandaki Area ...... 227 16.2 ––Ganesh Himal Area ...... 230 16.3 Annapurna Detachment ...... 230 16.4 Neighborhood of Ngadi–Marsyangdi Confluence ...... 233 References...... 235

17 Higher Himalaya of Bagmati–Gosainkund Region ...... 237 17.1 Kathmandu Complex...... 237 17.1.1 Bhimphedi Group ...... 237 17.1.2 Phulchauki Group ...... 240 17.1.3 Paleozoic Granites ...... 242 17.1.4 Gneisses and Migmatites ...... 242 17.1.5 Metamorphism ...... 242 17.2 Rasuwa Gadhi Area ...... 242 17.3 Sundarijal–Melamchi Area ...... 245 17.4 The Dhulikhel–Panchkhal Area...... 245 References...... 248

18 Higher Himalaya of Koshi Region ...... 251 18.1 Upper Tama Koshi Area ...... 251 18.1.1 Lesser Himalayan Sequence ...... 251 18.1.2 Higher Himalayan Crystallines ...... 252 18.2 Early Expeditions to Mount Everest ...... 253 18.3 Khumbu Neighborhood ...... 254 Contents xix

18.4 Metamorphism in the Dudh Koshi Area...... 255 18.5 Metamorphism Within Great Mahabharat Synform ...... 255 18.6 Sun Koshi–Kakur Khola Tract ...... 256 References...... 258

19 Higher Himalaya of Arun–Tamar Region ...... 259 19.1 Makalu–Arun Neighborhood ...... 259 19.1.1 Barun Gneisses (Gneiss du Barun) ...... 259 19.1.2 Barun Migmatites (Migmatites du Barun) ...... 260 19.1.3 Black Gneisses (Gneiss Noirs) ...... 260 19.1.4 Makalu Granite...... 262 19.1.5 Everest Series...... 262 References...... 264

20 Models of Himalayan Metamorphism ...... 267 20.1 Metamorphism and Related Modeling ...... 267 20.1.1 Shear (Frictional) Heating ...... 267 20.1.2 Conductive Heating...... 268 20.1.3 Downbowed Isotherms ...... 269 20.1.4 Intracontinental Subduction ...... 269 20.1.5 Shear Heating Accompanying Thermal Relaxation ...... 270 20.1.6 Synmetamorphic Deformation...... 271 20.1.7 Delamination of the Lithosphere ...... 271 20.1.8 Metamorphism in Thickened Continental Crust and PTt Paths ...... 273 20.1.9 Polyphase Metamorphism ...... 274 20.1.10 Post-metamorphic Imbrication ...... 275 20.1.11 Lateral Extrusion and Channel Flow ...... 275 20.1.12 Metamorphic Transformation in the Lower Crust ...... 276 20.1.13 Late Miocene Activation of the Main Central Thrust ...... 277 20.1.14 Intrusion of Hot Magma in the Upper Part of Main Central Thrust ...... 278 20.1.15 Thermomechanical Models Based on Channel Flow and Ductile Extrusion ...... 278 20.1.16 Critical Taper and Underplating Models...... 279 References...... 280

Part V Tethys Himalaya

21 Introduction to Tethys Himalaya...... 285 21.1 Early Fossil Finds ...... 286 21.2 Detailed Investigations of Ammonites ...... 288 21.3 Plant Fossils of Kagbeni ...... 288 21.4 Paleomagnetic Investigations in Thakkhola...... 288 21.5 Fossils from Phulchauki and Chandragiri Hills South of Kathmandu . . . . 288 References...... 292

22 Tethys Himalaya of Mahakali Region ...... 295 22.1 Garbyang Formation (Neoproterozic–) ...... 295 22.2 Shiala Formation (Ordovician) ...... 295 22.3 Variegated Silurian ...... 296 22.4 Muth Formation (late Silurian–Devonian) ...... 296 22.5 Kuling Formation or Productus Shale (Permian) ...... 296 22.6 Triassic ...... 299 xx Contents

22.6.1 Chocolate Formation ...... 299 22.6.2 Kalapani Limestone ...... 300 22.6.3 Tropites Limestone ...... 300 22.6.4 Kuti ...... 301 22.6.5 Kioto Limestone ...... 301 22.7 Laptal (or Lapthal) Formation...... 301 22.8 Ferruginous Oolite ...... 302 22.9 Spiti Shales ...... 302 22.10 Giumal Sandstone (Lower Flysch) ...... 303 22.11 Upper Flysch ...... 303 22.12 Structure ...... 303 References...... 304

23 Tethys Himalaya of Karnali–Bheri Region (Dolpa)...... 305 23.1 Dhaulagiri Limestone (?Cambrian–Ordovician) ...... 305 23.2 Silurian ...... 307 23.3 Muth Formation (Devonian) ...... 308 23.4 Tilicho (or Ice) Lake Formation (Carboniferous) ...... 309 23.5 Thini Chu Formation (Permian) ...... 309 23.6 Tamba Kurkur Formation (Early Triassic) ...... 310 23.7 Mukut Limestone (Anisian–Carnian) ...... 312 23.8 Tarap Shales (Carnian–Norian) ...... 313 23.9 Quartzite Series (Rhaetian)...... 313 23.10 Kioto Limestone (Rhaetian–Middle Jurassic) ...... 313 23.11 Lumachelle Formation (Bathonian–Callovian)...... 313 23.12 Spiti Shales (Tithonian–Early Cretaceous) ...... 314 23.13 Structure of Dolpa ...... 314 References...... 314

24 Tethys Himalaya of Gandaki Region (Thakkhola) ...... 317 24.1 Augen Gneisses and Larjung Formation (? Cambrian) ...... 317 24.2 Nilgiri Limestone and North Face Quartzite (Ordovician)...... 318 24.3 Pitted Calc-Schists Member and Dark Band Formation (Middle Ordovician—Early Devonian)...... 320 24.4 Tilicho Pass Formation (Middle–Late Devonian)...... 322 24.5 Tilicho Lake and Thini Chu Formations (Carboniferous–Permian)...... 323 24.6 Permo–Triassic Syn-rift Sediments ...... 326 24.7 Early Triassic ...... 327 24.8 Middle Triassic (Anisian and Ladinian) ...... 328 24.9 Late Triassic (Carnian and Norian) ...... 329 24.10 Latest Triassic (Rhaetian)...... 331 24.11 Triassic Lithostratigraphy...... 332 24.11.1 Tamba Kurkur Formation (Early Triassic) ...... 332 24.11.2 Lower Part of Mukut Formation (? Ladinian–Early Carnian) . . . 332 24.11.3 Upper Part of Mukut Formation (Late Carnian) ...... 333 24.11.4 Tarap Shale (Norian)...... 333 24.11.5 Thini Formation (Quartzite Formation, Late Norian–Rhaetian). . . 333 24.12 Early Jurassic ...... 333 24.13 Middle Jurassic...... 336 24.13.1 Lateral Continuity ...... 338 24.14 Late Jurassic ...... 338 24.15 Jurassic Lithostratigraphy...... 339 24.15.1 Jomosom Limestone (Kioto Limestone, Early Jurassic) ...... 339 24.15.2 Bagung Formation (Lumachelle Beds and Ferruginous Oolite, Bajocian–Early Callovian) ...... 340 Contents xxi

24.15.3 Nupra Formation (Spiti Shales, Middle Oxfordian–Tithonian). . . 340 24.16 Cretaceous ...... 341 24.16.1 Beginning of Early Cretaceous ...... 341 24.16.2 Barremian–Early Aptian ...... 342 24.16.3 Late Aptian–Late Albian ...... 342 24.17 Depositional Environment of Mesozoic Sediments ...... 343 24.18 Structure ...... 343 References...... 343

25 Tethys Himalaya of Gandaki Region (Manang) ...... 345 25.1 Early Paleozoic...... 345 25.2 Early Paleozoic Lithostratigraphy ...... 348 25.2.1 Marbles of Mutsog and Traglung or Larjung Formation (?Cambrian) ...... 348 25.2.2 Pi and Drongkhang Formations, Equivalents of Nilgiri Limestone (Early and Middle Ordovician) ...... 349 25.2.3 Quartzites of Gyaru or North Face Quartzite (Middle–Late Ordovician) ...... 349 25.2.4 Black Schists and Carbonates of Gyaru or Dark Band Formation (Ordovician–? Devonian) ...... 351 25.3 Devonian ...... 351 25.4 Devonian Lithostratigraphy ...... 351 25.4.1 Bangba or Tilicho Pass Formation (Devonian) ...... 351 25.5 Carboniferous and Permian ...... 353 25.6 Carboniferous and Permian Lithostratigraphy ...... 357 25.6.1 Tilicho Lake or Bangba Gompa Formation (Early Carboniferous) ...... 357 25.6.2 Thini Chu or Chulu Formation (Middle Carboniferous–Permian)...... 357 25.7 Triassic ...... 358 25.8 Triassic Lithostratigraphy...... 358 25.8.1 Tamba Kurkur Formation (Earliest Triassic–Early Anisian) . . . . 358 25.8.2 Mukut Limestone (Middle–Late Triassic)...... 358 25.8.3 Tarap Shales and Coral Limestone (Late Triassic)...... 359 25.8.4 The Rhaetian or Quartzite Beds (Late Triassic)...... 359 25.9 Jurassic ...... 359 25.9.1 Kioto or Jomosom Limestone (Early Jurassic) ...... 359 25.9.2 Lumachelle Formation (Middle Jurassic: Bajocian–Bathonian) ...... 360 References...... 360

26 Tethys Himalaya of Koshi Region (Mount Everest and Neighborhood) .... 361 26.1 Cambro–Ordovician ...... 362 26.2 Ordovician ...... 362 26.3 Silurian ...... 364 26.4 Devonian ...... 364 26.5 Carboniferous...... 364 26.6 Permian ...... 365 26.7 Triassic ...... 365 26.8 Jurassic ...... 366 26.9 Cretaceous ...... 366 26.10 Tertiary ...... 367 References...... 368 xxii Contents

Part VI Siwaliks

27 Introduction to Siwaliks ...... 371 27.1 Early Investigations in India and ...... 372 27.2 Stratigraphic Classification of Northwest Sub-Himalaya ...... 373 27.3 The Threefold Classification of Siwaliks ...... 373 27.3.1 Lower Siwaliks...... 373 27.3.2 Middle Siwaliks ...... 374 27.3.3 Upper Siwaliks...... 374 27.4 Problems of Threefold Usage and Terminology ...... 374 27.5 Other Classifications ...... 375 27.6 Investigations in Nepal ...... 375 27.7 Fossil Occurrence ...... 376 27.7.1 Fossils from the Nepalese Siwaliks ...... 377 27.8 Depositional Environment and Sedimentation Rates ...... 379 References...... 381

28 Siwaliks of Mahakali–Seti Region ...... 385 28.1 Lower Siwaliks...... 385 28.2 Middle Siwaliks ...... 386 28.3 Upper Siwaliks and Kalena Alluvial Fan ...... 388 28.4 Gravel Veneer East of Budar ...... 388 28.5 Structure of the Siwalik Belt ...... 389 References...... 390

29 Siwaliks of Karnali–Bheri Region ...... 391 29.1 Bankas Formation...... 391 29.2 Chor Khola Formation...... 392 29.2.1 Jungli Khola Member ...... 392 29.2.2 Shivgarhi Member ...... 393 29.3 Surai Khola Formation ...... 394 29.4 Dobata Formation ...... 398 29.5 Dhan Khola Formation ...... 402 29.6 Petrography of ...... 403 29.7 Structures...... 407 References...... 408

30 Siwaliks of Gandaki Region ...... 409 30.1 Arung Khola Formation...... 409 30.2 Binai Khola Formation ...... 412 30.3 Chitwan Formation ...... 414 30.4 Deorali Formation...... 414 30.5 Sandstone Petrography ...... 414 30.6 Paleocurrents ...... 414 30.7 Fossil Occurrence ...... 416 30.8 Paleomagnetism and Regional Correlation ...... 417 30.9 Structure ...... 417 References...... 417

31 Siwaliks of Bagmati–Gosainkund Region ...... 419 31.1 Lithostratigraphy...... 419 31.2 Lithofacies ...... 421 31.3 Structure ...... 423 31.4 Discontinuous Lesser Himalayan Belt ...... 425 References...... 426 Contents xxiii

32 Siwaliks of Koshi Region...... 427 32.1 Lithostratigraphy...... 427 32.2 Structure ...... 429 32.3 Development of Siwalik Wedge ...... 430 References...... 431

33 Siwaliks of Arun–Tamar Region ...... 433 33.1 Lesser Himalayan Sequence ...... 433 33.2 Siwaliks...... 433 33.3 Geomorphology ...... 436 33.4 Structure ...... 436 References...... 438

Part VII Terai, Intermontane Basins, and Neotectonics

34 Terai and Intermontane Basins ...... 441 34.1 Subsurface Configuration of Terai...... 441 34.2 Dang and Deukhuri Valley Fills ...... 441 34.2.1 Tectonic Interpretations ...... 445 34.3 Sediments of Pokhara and Neighborhood...... 445 34.3.1 Origin of Lakes ...... 448 34.3.2 Tectonic Implications ...... 448 34.4 Kathmandu Basin Fill ...... 448 34.4.1 Paleoclimate in Kathmandu Valley ...... 453 34.5 Thakkhola–Mustang Graben...... 453 34.5.1 Dangarjong Zone ...... 457 34.5.2 Tectonic and Environmental Interpretations ...... 457 References...... 457

35 Neotectonics ...... 461 35.1 and Mountain Building...... 461 35.2 Neotectonic Movements in the Northwest Himalaya and ...... 463 35.3 Active Faults in Nepal...... 463 35.3.1 Rangun Khola Active Fault ...... 464 35.3.2 Talphi Active Fault ...... 464 35.3.3 Surkhet–Ghorahi Active Fault ...... 464 35.3.4 Pressure Ridge Along Main Boundary Active Fault...... 466 35.3.5 Bari Gad Fault ...... 466 35.3.6 Kolphu Khola Fault ...... 466 35.3.7 Tilted Fanglomerates in the Goyeng Khola, East Nepal ...... 466 35.4 Change in Drainage of Major Rivers ...... 467 35.5 Elevated River Terraces ...... 467 35.6 Rupture Due to Great Assam Earthquake of 1897 ...... 468 35.7 Deformation Related to the Great Kangra Earthquake of 1905 ...... 469 35.8 Measuring Neotectonic Movements...... 471 35.9 Microseismicity in Nepal ...... 473 35.10 A Comparison with the Subduction Zone...... 473 References...... 475

36 Conclusions ...... 479 36.1 Lesser Himalaya ...... 479 36.2 Higher Himalaya ...... 481 36.2.1 Some Remarks on Inverted Metamorphism ...... 482 36.3 Tethys Himalaya...... 483 xxiv Contents

36.4 Siwaliks...... 484 36.5 Neotectonics...... 484 36.6 East Versus West Himalaya ...... 485 36.7 Some Anomalies...... 485 References...... 485

Index ...... 487