HR: 1340h
AN: T23C-0576    [Abstracts]
TI: Glacial erosion, deep exhumation and the development of high topography along the Kongur detachment, Pamir Mountains, Western China
AU: * Schoenbohm, L
EM: schoenbohm.1@osu.edu
AF: Ohio State Univesity, Dept. of Geoscience, ML275, 125 S Oval Mall, Columus, OH 43210 United States
AU: Jie, C
EM: jie_chen_66@yahoo.com
AF: Institue of Geology, China Earthquake Administration, PO Box 9803, Beijing, 100029 China
AU: Sobel, E
EM: sobel@rz.uni-potsdam.de
AF: University of Potsdam, Insitute of Geosciences, Postfach 601553, Potsdam, 14415 Germany
AU: Thiede, R
EM: thiede@geo.uni-potsdam.de
AF: University of Potsdam, Insitute of Geosciences, Postfach 601553, Potsdam, 14415 Germany
AU: Strecker, M
EM: strecker@geo.uni-potsdam.de
AF: University of Potsdam, Insitute of Geosciences, Postfach 601553, Potsdam, 14415 Germany
AB: Glacial erosion is linked to rapid exhumation and the formation of anomalously high peaks along the Kongur detachment fault in the Chinese Pamir. The footwall of the N-S detachment forms a high range along the eastern border of the Pamir that increases in elevation to the south, culminating in the twin peaks Kongur Shan (7719 m) and Muztagh Ata (7546m). The rocks underlying the peaks have experienced significantly more exhumation than those in the north (Robinson et al., 2004) and form broad domes. In the hanging wall valley to the west, the trunk river is forced to the west side of the valley by Quaternary/Holocene(?) debris shed from the footwall range. This observation and the relatively thinness of sediments in the valley indicate footwall uplift rather than hanging wall subsidence. This leads to higher peak elevations in the footwall, increasing the landscape area above the ELA. We suggest a scenario in which initial structural unroofing of the footwall, increased peak height and the resulting orographic focusing of precipitation may have led to increased glacial erosion. Glaciation would have been most significant in the south where the peaks were highest. The additional component of exhumation in the southern regions then drove greater structural exhumation, maintaining high topography and establishing a climate-moderated feedback loop. In order to understand the importance of glaciation in this scenario, we look to understanding temporal and spatial erosion and deposition in the valley. Three glacial sequences (moraine deposition, terrace formation, erosion) are recorded in the hanging wall valley, successively decreasing in extent. The extent of glaciation varies significantly from the north, where moraines are limited to the mouths of tributary valleys, to the south, where moraines completely filled the main valley. This variation is the result of the southward increasing range height and landscape area above the ELA. With moraine volume as a proxy for relative glacial erosion, we confirm that glacial erosion increases in concert with peak elevations and degree of exhumation. A direct link between erosion and accelerated exhumation, however, can only be established with age data because of the variability of glacial erosion on both short term (single glacial cycle) and long term (onset of northern hemisphere glaciation ca. 2.75 Ma) time scales. Correlation of the sequence observed here to other, dated sequences in the region is difficult because of microclimate variability and strong topographic affects. We therefore are undertaking work to date this sequence of moraines and terraces directly, and to constrain the footwall exhumation history.
DE: 1815 Erosion
DE: 1827 Glaciology (0736, 0776, 1863)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8175 Tectonics and landscape evolution
DE: 8177 Tectonics and climatic interactions
SC: Tectonophysics [T]
MN: Fall Meeting 2005