HR: 1340h
AN: T23D-1651    [Abstracts]
TI: Exhumation and Uplift of the Shillong Plateau and its Influence on the Eastern Himalayas: new Constraints From Apatite and Zircon (U-Th-[Sm])/He and Apatite Fission Track Analyses
AU: Biswas, S
AF: Jahangirnagar University, Department of Geological Sciences Savar, Dhaka, 1342, Bangladesh
AU: * Coutand, I
AF: Universite de Lille 1, UMR-CNRS 8110 Processus et Bilan des Domaines Sédimentaires Cite Scientifique, Bat SN5, Villeneuve d'Ascq, 59655, France
AU: Grujic, D
AF: Dalhousie University, Department of Earth Sciences, Halifax, NS B3H 4J1, Canada
AU: Hager, C
AF: University of Kansas, Department of Geology, Lawrence, KS 66045-7613, United States
AU: Stöckli, D
AF: University of Kansas, Department of Geology, Lawrence, KS 66045-7613, United States
AU: Grasemann, B
AF: University of Vienna, Center for Earth Sciences Althanstrasse 14, Vienna, A-1090, Austria
AB: The Shillong plateau is the only raised topography in the foreland of the Himalayas. Located on the trajectory of the Indian Summer Monsoon (ISM), the plateau perturbs the regional distribution of precipitation. As such the Shillong plateau-eastern Himalaya-ISM is a unique system to quantify the couplings between climate, tectonics and erosion. A change in long-term erosion rates along-strike the Bhutan Himalaya was recently attributed to a climatic modulation due to the uplift of the Shillong plateau. To test this interpretation, it is essential to constrain the timing and rate at which the plateau was uplifted and the amount of partitioning of the India-Asia convergence into the plateau. We used apatite and zircon (U-Th-[Sm])/He and apatite fission-track analyses to unravel the thermal histories of thirteen basement samples collected along a N-S transect across the central Shillong plateau. We find that 1) the exhumation of the plateau began at least 9-15 Ma ago, 2) its surface uplift was chronologically decoupled from its exhumation and started after ~3-4 Ma at rates of 0.4-0.53 mm/yr, 3) the long- term horizontal shortening rate accommodated by the plateau is 0.65-2.3 mm/yr, which represents only 10-15 percent of the India-Asia convergence rate. The uplift of the Shillong plateau did not significantly modify the rock uplift rate in the Bhutan Himalaya, which is consistent with the hypothesis of climatic modulation of the Pliocene erosion, tectonic and landscape evolution previously documented along this orogenic front.
DE: 1140 Thermochronology
DE: 8175 Tectonics and landscape evolution
DE: 8177 Tectonics and climatic interactions
DE: 9320 Asia
SC: Tectonophysics [T]
MN: 2007 Fall Meeting