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 Nepal 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 Library of Congress Control Number: 2014949333 © Springer International Publishing Switzerland 2015 This work is subject to copyright. 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Printed on acid-free paper 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 Proterozoic 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 tectonics 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 India. 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 metamorphism 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 Terai 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.