HR: 1330h
AN: H42C-1097    [PDF]
TI: How does the distribution of orographic precipitation guide exhumation patterns along the Southern Himalayan front, NW India?
AU: * Thiede, R C
EM: thiede@geo.uni-potsdam.de
AF: Institute of Geosciences, University of Potsdam Postfach 60 15 53, Potsdam, 14415 Germany
AU: Bookhagen, B
EM: Bodo@geo.uni-potsdam.de
AF: Institute of Geosciences, University of Potsdam Postfach 60 15 53, Potsdam, 14415 Germany
AU: Strecker, M R
EM: strecker@geo.uni-potsdam.de
AF: Institute of Geosciences, University of Potsdam Postfach 60 15 53, Potsdam, 14415 Germany
AU: Arrowsmith, J
EM: ramon.arrowsmith@asu.edu
AF: Department of Geological Sciences, Arizona State University, Tempe, AZ 85287-1404 United States
AU: Sobel, E R
EM: ed@geo.uni-potsdam.de
AF: Institute of Geosciences, University of Potsdam Postfach 60 15 53, Potsdam, 14415 Germany
AU: McWilliams, M
EM: mcwilliams@stanford.edu
AF: Geological & Environmental Sciences, Stanford University, Stanford, CA 94305-2115
AB: A strong climatic contrast exist across the Himalaya, whereas the Southern Himalayan Front (SHF) is affected by strong monsoonal precipitation, the internal region between the High Himalaya and the Indus-Tsangpo suture zone to the north is dry. When during the Indian summer monsoon the humid airflow has to cross the Himalaya, it is controlled and funneled by the topography. This result in asymmetric precipitation distribution concentrated in elevations of 2000 to 4000 m along the southern termination of the High Himalaya and provides a high seasonal fluvial runoff, which enables an effective sediment evacuation out of the range. The High Himalaya is actively deforming as indicated by young cooling ages, micro-seismicity, and geodetic data. In the area of the Sutlej River (NW-India) the deeper high-grade metamorphic rocks of High Himayalan and Lesser Himalayan Crystalline are being exhumed as an extruding wedge. Active deformation of the orogen coincides with high monsoonal precipitation, pronounced relief contrasts, steep river gradients and slope angles that predispose these rocks to effective mass removal. But how and if this inhomogeneous distribution of precipitation affects mountain building processes of the Himalayan range is still controversial. New young apatite fission track (AFT) ($<$1-5 Ma; 30 dates) and 40Ar/39Ar (20 dates) ages from the greater Sutlej area document rapid exhumation of high-grade metamorphic Lesser and Higher Himalayan Crystalline units. Two AFT sample transects are sampled in the range between 1.5 and 4.5 km in elevation along tributaries perpendicular to the Sutlej River. The AFT samples yield ages between $<$1-4 Ma and correlate with elevation. Compiled regional distribution of AFT ages document a $\sim$50 km long sector where the Sutlej River is crossing the southern termination of the High Himalaya (main orographic barrier), and AFT samples provide young cooling ages of $\sim$1 Ma. Assuming uniform long-term steady-state erosion and exhumation, the rocks were exhumed at a rate of $\sim$1 mm/a during Plio-Pleistocene time. Samples collected near to the riverbanks of the Sutlej further upstream or downstream yield older cooling ages ($>$3 Ma). The sectors with high exhumation rates correlate with maxima in the distribution of monsoonal precipitation, where the orographic precipitation barrier results in $>$80% of the annual precipitation. These results suggest a strong interaction between rapid erosion, exhumation, and sediment evacuation concentrated in a $\sim$50-km-wide sector of the Himalayan deformation belt. Thus, this sector may define an extruding wedge whose principal boundaries are defined by climatically controlled erosional processes.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1854 Precipitation (3354)
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2003 Fall Meeting