HR: 17:40h
AN: T34C-09    [Abstracts]
TI: Construction of the Eastern Himalaya by Thick-skinned Thrust Stacking of the Indian Basement: No Lower Crustal Flow from Tibet is Needed
AU: * Yin, A
EM: yin@ess.ucla.edu
AF: Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, United States
AU: Dubey, C S
AF: Department of Geology, Delhi University, Delhi, 110007, India
AU: Kelty, T K
AF: Department of Geological Sciences, California State University, Long Beach, CA 90840, United States
AU: Webb, A A
AF: Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, United States
AU: Gehrels, G E
AF: Department of Geosciences, University of Arizona, Gould-Simpson Building #77, 1040 E 4th St, Tucson, AZ 85721, United States
AU: Harrison, T M
AF: Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, United States
AU: Celerie, J
AF: Research School of Earth Sciences, Building 61, Mills Road, the Australian National University, Canberra, ACT 0200, Australia
AU: Dai, J
AF: Research Center for Tibetan Plateau Geology, China University of Geosciences, Beijing, 100083, China
AB: A geologic investigation integrating filed mapping, geochronology and geochemistry across the Eastern Himalaya at the longitude of 91-93E has led to the following findings and interpretations. (1) The Triassic flysch complex in the North Indian Sequence (also known as the Tethyan Himalayan Sequence) was sourced from the Lhasa terrane (not India!). Thus, geochemical signatures of Cenozoic intrusive rocks alone in the northern Himalaya are insufficient to test whether the Tibetan lower crust has extruded ductilely below the Himalayan orogen, because India and Lhasa shared the same basement geology prior to the opening of the Neo-Tethys in the Triassic and early Jurassic. (2) The Main Central Thrust warps over a large thrust duplex. The total amount of shortening across the fault and its footwall thrusts exceeds 500 km. This estimate may include contribution from an early Paleozoic contractional event that is at the present difficult to be distinguished from Cenozoic strain. Work is in progress in the Shillong Plateau to resolve this issue. (3) Our U-Pb zircon dating together with the existing geochronologic results indicates that the ages of Eastern Himalayan orthogneisses cluster at 500 Ma, 870 Ma, 1100 Ma, and 1770 Ma, respectively. These ages correlate well with those found in the Shillong Plateau of the Indian basement, immediately south of the Eastern Himalaya. The lithologic correlation between the Himalayan and Indian basement units implies that the construction of the Eastern Himalaya was accomplished by thick- skinned, basement-involved thrusting. Motion on the deeply rooted thrusts has stacked and thus thickened the Indian basement to form the Eastern Himalayan orogen.
DE: 8100 TECTONOPHYSICS
DE: 8110 Continental tectonics: general (0905)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting