Downloaded from gsabulletin.gsapubs.org on July 5, 2010 Geological Society of America Bulletin Geologic correlation of the Himalayan orogen and Indian craton: Part 2. Structural geology, geochronology, and tectonic evolution of the Eastern Himalaya An Yin, C.S. Dubey, T.K. Kelty, A.A.G. Webb, T.M. Harrison, C.Y. Chou and Julien Célérier Geological Society of America Bulletin 2010;122;360-395 doi: 10.1130/B26461.1 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geological Society of America Bulletin Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education and science. This file may not be posted to any Web site, but authors may post the abstracts only of their articles on their own or their organization's Web site providing the posting includes a reference to the article's full citation. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Notes © 2010 Geological Society of America Downloaded from gsabulletin.gsapubs.org on July 5, 2010 Geologic correlation of the Himalayan orogen and Indian craton: Part 2. Structural geology, geochronology, and tectonic evolution of the Eastern Himalaya An Yin1,2,†, C.S. Dubey3, T.K. Kelty4, A.A.G. Webb1, T.M. Harrison1, C.Y. Chou1, and Julien Célérier5 1Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095-1567, USA 2Structural Geology Group, School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 10083, China 3Department of Geology, Delhi University, Delhi-110007, India 4Department of Geological Sciences, California State University, Long Beach, California 90840-3902, USA 5Research School of Earth Sciences, Building 61, Mills Road, Australian National University, Canberra, ACT 0200, Australia ABSTRACT etry. Crustal thickening of the Main Central 1985), (2) southward propagation of a thin- thrust hanging wall was expressed by dis- skinned thrust belt (e.g., Schelling and Arita, Despite being the largest active collisional crete ductile thrusting between 12 Ma and 1991; Srivastava and Mitra , 1994; DeCelles orogen on Earth, the growth mechanism of 7 Ma, overlapping in time with motion on et al., 1998, 2001, 2002; Avouac, 2003; Robinson the Himalaya remains uncertain. Current the Main Central thrust below. Restoration et al., 2003, 2006; Robinson and Pearson, 2006; debate has focused on the role of dynamic of two possible geologic cross sections from Kohn, 2008), and (3) southward transport of inter action between tectonics and climate one of our geologic traverses, where one as- high-grade metamorphic rocks via lower-crustal and mass exchanges between the Hima- sumes the existence of pre-Cenozoic defor- channel fl ow or wedge extrusion (Burchfi el and layan and Tibetan crust during Cenozoic mation below the Himalaya and the other Royden , 1985; Chemenda et al., 1995, 2000; India-Asia collision. A major uncertainty in assumes fl at-lying strata prior to the India- Grujic et al., 1996; Nelson et al., 1996; Grase- the debate comes from the lack of geologic Asia collision, leads to estimated shortening mann et al., 1999; Beaumont et al., 2001, 2004, information on the eastern segment of the of 775 km (~76% strain) and 515 km (~70% 2006; Hodges et al., 2001; Grujic et al., 2002; Himalayas from 91°E to 97°E, which makes strain), respectively. We favor the presence of Searle et al., 2003; Klemperer, 2006; Godin up about one-quarter of the mountain belt. signifi cant basement topog raphy below the et al., 2006). The central issue with the afore- To address this issue, we conducted detailed eastern Himalaya based on projections of mentioned models is that they were all estab- fi eld mapping, U-Pb zircon age dating, and early Paleo zoic structures from the Shillong lished from the geology of the central Himalaya 40Ar/39Ar thermo chronology along two geo- Plateau (i.e., the Central Shillong thrust) lo- in Nepal and south-central Tibet (77°E–88°E), logic traverses at longitudes of 92°E and cated ~50 km south of our study area. Since where the classic Himalayan relationships as 94°E across the eastern Himalaya. Our dat- northeastern India and possibly the eastern originally defi ned by Heim and Gansser (1939) ing indicates the region experienced mag- Himalaya both experienced early Paleozoic are exposed (Fig. 1). That is, the Main Bound- matic events at 1745–1760 Ma, 825–878 Ma, contraction, the estimated shortening from ary thrust places the Lesser Himalayan Se- 480–520 Ma, and 28–20 Ma. The fi rst three this study may have resulted from a com- quence over Tertiary strata, the Main Central events also occurred in the northeastern In- bined effect of early Paleozoic and Cenozoic thrust places the Greater Himalayan Crystalline dian craton, while the last is unique to the deformation. Complex over the Lesser Himalayan Sequence, Hima laya. Correlation of magmatic events and the later discovered South Tibet detachment and age-equivalent lithologic units suggests INTRODUCTION places the Tethyan Himalayan Sequence over the that the eastern segment of the Himalaya Greater Himalayan Crystalline Complex (e.g., was constructed in situ by basement-involved The Himalayan orogen was created by the LeFort, 1996; Yin and Harrison, 2000). These thrusting, which is inconsistent with the hy- Ceno zoic India-Asia collision starting at ca. 65– studies generally neglect signifi cant differences pothesis of high-grade Himalaya rocks de- 60 Ma (Yin and Harrison, 2000; Ding et al., in geological relationships along the Himalayan rived from Tibet via channel fl ow. The Main 2005) or earlier (e.g., Zhu et al., 2005; Aitchison strike and have treated Himalayan evolution as Central thrust in the eastern Himalaya forms et al., 2007). Although its plate-tectonic setting a two-dimensional problem in cross-section the roof of a major thrust duplex; its north- is well understood, the growth mechanism of view. As pointed out by DiPietro and Pogue ern part was initiated at ca. 13 Ma, while the orogen remains debated. Competing mod- (2004), Yin (2006), and Webb et al. (2007), such the southern part was initiated at ca. 10 Ma, els emphasizing different controlling factors in- an approach may disguise critical information as indicated by 40Ar/39Ar thermochronom- clude: (1) vertical stacking of basement-involved on the mechanism of the Himalayan develop- thrust sheets (Heim and Gansser, 1939; Gansser, ment when the regional map relationship across †E-mail: [email protected] 1964; LeFort, 1975; Lyon-Caen and Molnar, the whole orogen is not fully considered. For GSA Bulletin; March/April 2010; v. 122; no. 3/4; p. 360–395; doi: 10.1130/B26461.1; 15 fi gures; 2 tables. 360 For permission to copy, contact [email protected] © 2009 Geological Society of America America Bulletin,March/April2010 Geological Societyof 361 Indus R Cz, Cenozoic foreland basin 100°E Bangong- Downloaded from THS, Tethyan Himalayan Sequence Bangong- Nujiang sediments K-Cz, Cretaceous-Cenozoic LHS, Lesser Himalayan Sequence and age- Nujiang Cz . suture 32°NN sediments equivalent strata in the Shillong Plateau suture Qiangtang Jurassic to early Tertiary GHC, Greater Himalayan Sequence and terrane Gangdese batholith (150-50 Ma) age-equivalent rocks in the Shillong Plateau Sutlej R. Mt. Kailas P, Permian Gondwana Sequence Lake Mekong R. Jinsha suture Yalong R. Zari Nam Co Lhasa terrane MFT Nam Co Ga n South g 30°N gsabulletin.gsapubs.org 76°E7 NWN India de 78°E Indus- se China HimalayaHimHiimalayaimal B Tsangpo ath Parlung R. block Bhagirathi R. olith B B suture elt Fig. 2 Namche Barwa Yan (7782 m) YaluTsangpo gtze R. Siang E. A 40°N Window STD rur A Irraw Tarim Basin iri n n R. Subans R. H imam THS addy R. 28°N A STD ma.m K-Cz a. NepalN Tibetan Plateau Hima.H ma.a. AArun MCT MCT SikkimSikkiS KZT W. Arun. Hi BT A P Fig. 13 I n Hima.H H d Kameng R us GHC im -T sa Fig. 1B 30°N Bhutanan . al ng 84°E s Salween R. a p BT l onJuly5,2010 y o su LHS il Indus- an ture MBT Hima. H R. a Tsangpo Orog s R g en 86°E TT a R. N ra suture Teesta anas ut M ap K-Cz d 90°E Brahm n Kali Gandaki R. Indo-Burma- I 88°E xln Indian Peninsular Arun R. R Eastern Himalaya . Andaman Highlands Shillong Plateau Pt 20°N 0 100 200 km terrane Jamuna R. 70°E 80°E 90°E 100°E 92°E929 94°E94 E 96°E 100°E10 Figure 1. (A) A sketch map of the Himalayan-Tibetan orogen. (B) Regional geologic map of the Himalayan orogen simplifi ed from Yin and Harrison (2000) and Yin (2006). Locations of Figures 2 and 13 are also shown. Abbreviations for major faults: MFT—Main Fron- tal thrust; MBT—Main Boundary thrust; MCT—Main Central thrust; STD—South Tibet detachment; BT—Bome thrust; TT—Tipi thrust.