HR: 0800h
AN: T31D-0673    [Abstracts]
TI: Geochronoloical Evidence for Correlation between the Eastern Himalayan and northern Indian basement units: Implications for the mechanism of Himalayan Construction
AU: * Webb, A A
EM: awebb@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: 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
AF: Department of Geology, Delhi University, Delhi, 110007, India
AU: Gehrels, G E
AF: Department of Geosciences, University of Arizona, 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
AB: Central to determining the mechanism of Himalayan formation is the tectonic origin of the Greater Himalayan Crystalline Complex (GHC) and its relationships to the Lesser Himalayan Sequence (LHS), Tethyan Himalayan Sequence (THS), and Tibetan and Indian basement rocks. The GHC is hypothesized to be derived from Indian basement, Tibetan lower crust, or an exotic terrane, each making distinctive predictions of their protoliths and implying different kinematic histories and thus dynamic controls for the Himalayan development. To differentiate the above models, we conducted a preliminary U-Pb zircon geochronologic study across the Eastern Himalaya at longitude 91-93E from the Indus-Tsangpo suture in the north to the Shillong plateau in the south. Our results indicate that the orthogneiss units in the GHC and LHS, which are abundant in the Eastern Himalaya, have similar mineral composition and structural fabrics with ages clustered at 1.75 Ga, 837 Ma, and 510 Ma, respectively. The orthogneiss ages coincide with those obtained from the Indian basement rocks in the Shillong plateau and Mikir Hills of NE India, where our own dating and the existing age data indicate that the crystalline basement consists of meta-granites with ages clustered at 1.74 Ma, 1.1 Ga, and 800-860 Ma. Detrital zircon ages of the GHC and LHS from the Eastern Himalaya overlap significantly with one another, having peaks at 1.1 Ga and 1.7 Ga that can be attributed to a source from the Indian basement. The detrital zircon ages of the GHC and LHS are also similar to those obtained from the Proterozoic Shillong Group overlying the Indian basement and intruded by 520-500 Ma granites. The above age correlation suggests that the Precambrian orthogneiss units in the Eastern Himalaya were parts of the Indian crystalline basement and the meta-sedimentary rocks of the GHC and LHS were probably parts of the Proterozoic cover sequence above the basement. Our interpreted lithostratigraphy prior to the Indo-Asian collision across the Eastern Himalaya indicates that the orogen formed by thick-skinned thrusting involving Indian crystalline basement rocks.
DE: 8100 TECTONOPHYSICS
DE: 8110 Continental tectonics: general (0905)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting