Stratigraphy of the Tethys Himalaya and the Age of the India/Asia Collision

Monday, 15 December 2014: 11:05 AM
Eduardo Garzanti, University of Milan - Bicocca, Milan, Italy; University of Milano-Biccocca, Earth and Environmental Sciences, Milano, Italy and Xiumian Hu, University of Nanjing, School of Earth Sciences and Engineering, Nanjing, China
The Tethys Himalayan stratigraphic record (Sciunnach and Garzanti 2012 Earth Sci.Rev.) excludes any postulated orogenic event associated with ophiolite obduction, arc–continent, or continent–continent collision in the Late Cretaceous, when multifold increase in terrigenous supply indicates dynamic upwelling heralding the Deccan megaeruptions (Garzanti and Hu 2014 Gondwana Res.). In the Paleocene, quartzarenites deposited at subequatorial latitudes were followed by widespread carbonate-ramp deposits. Passive-margin carbonate sedimentation lasted until the earliest Ypresian in Zanskar (SBZ 7/8; 55-54 Ma; Nicora et al. 1987 Riv. It. Pal. Strat.; Jenks et al. 2009 EGU Abs.) and until the early Lutetian in south Tibet (SBZ 10 to SBZ 13a; 53-51 to 49-47 Ma). The unconformably overlying volcaniclastic to ophioliticlastic sediments document progradation of a shallow-marine to subaerial delta fed from the Asian margin in the north. These units seal Neotethyan history and testify that the India/Asia collision was well underway by the middle Ypresian in the Zanskar traverse (SBZ 9/10; 53-51 Ma; Green et al. 2008 J. Geol.; Jenks et al. 2009) and by the middle Lutetian in the Tibetan traverse (P11/early P12; 43 Ma), when even shallow seas finally withdrew from above the nascent proto-Himalaya. The India/Asia collision has long been dated at around the Paleocene/Eocene boundary (~56 Ma; Garzanti et al. 1987 Geodin. Acta) by the major unconformity identified within carbonate-platform sediments and ascribed to flexural uplift shortly following the arrival of the edge of continental India at the Transhimalayan trench (Zhang et al., 2012; DeCelles et al. 2014 Tectonics). Collision onset can be dated directly in deep-water successions of the distal Indian margin by radiolarian biostratigraphy coupled with zircon chronostratigraphy, but due to the uncertainties of both methods estimates range from ≥50 Ma (Wang et al. 2011 J. Geol.) to 60/58.5 Ma (DeCelles et al. 2014; Wu et al., 2014 Am. J. Sci.).