Geology of the Nepal Himalaya: Regional Perspective of the Classic Collided Orogen PDF
Preview Geology of the Nepal Himalaya: Regional Perspective of the Classic Collided Orogen
Regional Geology Reviews Megh Raj Dhital Geology of the Nepal Himalaya Regional Perspective of the Classic Collided Orogen Regional Geology Reviews Series editors Roland Oberhänsli Maarten J. de Wit François M. Roure For furthervolumes: 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 RajDhital Central Department ofGeology TribhuvanUniversity Kirtipur, Kathmandu Nepal ISBN 978-3-319-02495-0 ISBN 978-3-319-02496-7 (eBook) DOI 10.1007/978-3-319-02496-7 SpringerChamHeidelbergNewYorkDordrechtLondon LibraryofCongressControlNumber:2014949333 ©SpringerInternationalPublishingSwitzerland2015 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartofthematerialis concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed.Exemptedfromthislegalreservationarebriefexcerptsinconnectionwithreviewsorscholarlyanalysis ormaterialsuppliedspecificallyforthepurposeofbeingenteredandexecutedonacomputersystem,forexclusive use by the purchaser of the work. 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Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(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 earlycontributionswererestrictedtoisolatedsectors,leavingmanygapsintheunderstanding 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 publicationsandarrangedtheseintoseveralchapterswithinformativemaps,chartsandfigures 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 geologyasthetopography iscontrolledbytherocks. Political boundaries werecreated much after the Himalaya came into existence; the geological elements of Nepal, therefore, should findcontinuityintheadjoiningWesternandSoutheastHimalayaandthePeninsularIndia.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 theirexhaustiveaccount.ElaborationofcomplicatedgeologyoftheHigherHimalayaandthe enigmaofinvertedgradeofmetamorphismintheHimalayaisofinteresttooneandall.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.Neotectonicshavingenvironmentalsignificanceshouldbeamusttotheplannersand 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 Nepalgeology.ThisbookcompletesthepanoramaoftheHimalayangeologystretchingfrom 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- logicalinvestigationsinNepalbeganonlyin1951,exactly100yearsaftertheestablishmentof the Geological Survey of India. But, soon after, the geological literature on Nepal began to grow exponentially,andpresentlythenumberofpublicationshasbecometoonumerous,and the information is scattered worldwide through various books, periodicals, and unpublished reportsinmorethansevenlanguages.Therefore,itisdesirabletogather,amidstmanydetails, the important geological knowledge of the Nepal Himalaya and to go through the prevailing concepts,behindtheformationanddevelopmentofthistoweringmountainrangeoftheworld. Thisbookhasensuedfrommyresearchintotheexistinggeologicalliteratureaswellasits developmentaltrendintheHimalaya.Whilepreparingthebook,Ihavealsodrawnonmyown 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 geologicalcontact,sometheoreticalbackgroundisnecessary.However,oneofthedistinctive attributes of Himalayan geology is the proliferation of views on various geological phe- nomena,operatinginthis majestic mountainrealm. The geological literatureoftheHimalaya 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 shortinterval,ifwetakeintoaccountthelast200yearsofintenseandexhaustiveinvestigation oftheHimalaya byagamutofresearchersfromvariouscountriesoftheworld,theoutcomes haveprovedtobeastonishinglyfruitfulintheirapplicationtothewholeHimalayanRangeand also beyond its borders. Geologists do not spend whole of their life in theoretical discourses alone, but they do producearangeofgeologicalmaps,immenselyusefultothegovernmentalaswellasprivate organisationsintheirendeavourtodevelopconstructionmaterial-ormineral-basedindustries, 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, manydetailedgeologicalmapsofsomeparticularareasareincludedinthisbook.Sincemore thantwo-thirdsofthetotalareaofNepalishithertounmappedonalargescale,thereremains 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. Itisendeavouredtobringtogether,throughthisbook,thegeologyofthewholeHimalayan Range of Nepal, i.e., from the graceful grasslands of the Ganga basin on the south to the toweringTethyanzoneonthenorth.Thoughmanywritershavechosentodiscussthegeology oftheHimalayafromsouthtonorth,thisbookisarrangedsomewhatdifferently.Itisbecause, 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 introductiontotheHimalayaandneighboringregions,thebookdescribestheoldestsequence 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 scientificontology,butanattemptismadetorevealasoundbasistotheprevailingconcepts.It isanticipatedthatthebookwillhelpthereadertomoveforwardfromacognitiveapproachto a constructive one with the praxis of linking a variety of knowledge, including the earlier inferencesorviewsandcontemporarytheoriesormodels,wheretheintentofboththepastand 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.InformationwasalsogatheredfromTübingenUniversityandETHZürichlibraries.Ialso received a 4-month-long research fellowship from Hokkaido University. Nepal Academy of ScienceandTechnologyaswellasIndianNationalScienceAcademyfacilitatedmy3-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. Itwouldhavebeenimpossibletowritethisbookwithoutanenormousamountoftechnical 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, MadhavBelbase,AnantaPrasadGajurel,DineshPathak,LilaNathRimal,LaluPrasadPaudel, 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 GeologicalSurveyofAustriamadeavailablevariousbooksandjournalsaswellaspublished and unpublished reports. Many stimulating and fruitful discussions with Gerhard Fuchs and Wolfgang Frank clarified several issues related to tectonics and stratigraphy. 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 painstakingcorrectionsaswellasforgivingmanypracticalsuggestions.Healsofacilitatedmy field observations in Solan and Simla. xi
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