HR: 1340h
AN: T23D-1640    [Abstracts]
TI: A Climatic Trigger for Enhanced Late Cenozoic Exhumation of the Chinese Pamir?
AU: * Sobel, E R
EM: sobel@rz.uni-potsdam.de
AF: Universitaet Potsdam, Institut fuer Geowissenschaften Karl-Liebknecht-Strasse 24, Golm, 14476, Germany
AU: Thiede, R
EM: thiede@geo.uni-potsdam.de
AF: Universitaet Potsdam, Institut fuer Geowissenschaften Karl-Liebknecht-Strasse 24, Golm, 14476, Germany
AU: Schoenbohm, L
EM: schoenbohm.1@osu.edu
AF: Ohio State University, Dept. of Geological Sciences 275 Mendenhall Laboratory, Columbus, OH 43210, United States
AU: Chen, J
EM: chenjie@ies.ac.cn
AF: China Earthquake Administration, State Key Laboratory of Earthquake Dynamics Institute of Geology P.O.Box 9803, Beijing, 100029, China
AB: In the Chinese Pamir mountains at the western end of the Tibetan Plateau, two high peaks (Kongur Shan at 7719 m and Muztagh Ata at 7546 m), rise >4000 m above the plateau, representing an area of significant anomalous topography. These mountains are situated below the Kongur detachment, correspond with domal structures cored by gneisses exhumed since 6-8 Ma from up to 27 km depth (Robinson et al., GSAB, 2004). Exhumation of these domal structures is undoubtedly related to movement along the Kongur detachment fault. However, the locally more rapid exhumation rates in the area of these two domes, their association with extensive glaciers with headwalls up to 2 km high, and with deeply incised river gorges immediately to the north and south of the massifs point to additional exhumation of the domes driven by positive feedback between focused fluvial and glacial erosion and thermal and mechanical weakening of the crust. It is possible that glaciation is a passive result of tectonic exhumation, in which tectonically produced high peaks lead to greater orographic precipitation, resulting in the development of larger glaciers, or that the peaks are the location of a "tectonic aneurysm," driven to greater exhumation and height by focused glacial erosion. New apatite fission track (AFT) and argon data from both the footwall and hanging wall along the length of the detachment provide a more detailed view of the latest Cenozoic cooling history. In the north, along the Muji segment, and in the middle, near Kongur Shan, hanging wall AFT ages are 4-6 Ma. Footwall AFT ages in the Muji segment and in the south, along the upper Yarkand river are ca. 3 Ma. However, the footwall of the western flank of Kongur Shan yields AFT ages between 1 and 2 Ma, very similar to our own and published argon ages on biotite and muscovite, the oldest of which is 2.5 Ma (muscovite). Published argon MDD modeling of three feldspars from the northern flank of Kongur Shan show a significant increase in cooling rate at ca. 2 Ma. Our samples from closer to the detachment suggest that accelerated cooling started slightly earlier. The preliminary data implies that this acceleration in exhumation rate at ca. 3 Ma was roughly synchronous over ca. 150 km along the length of the detachment. The timing and spatial distribution of this event is more readily explained as a consequence of enhanced erosion due to climate change rather than a tectonic effect due to a change in the regional stress field. The largest magnitude and highest rate of exhumation is associated with the most significant , glaciated topography, suggesting a feedback between focused surface processes and exhumation.
DE: 1140 Thermochronology
DE: 1815 Erosion
DE: 8109 Continental tectonics: extensional (0905)
DE: 9320 Asia
DE: 9605 Neogene
SC: Tectonophysics [T]
MN: 2007 Fall Meeting