Glacial erosion, deep exhumation and the development of high topography along the Kongur detachment, Pamir Mountains, Western China

In the Pamir mountains of western China, in the footwall of the Kongur detachment, the correlation of the high peaks Kongur Shan (7719 m) and Muztagh Ata (7546m), large glaciers, exhumation of mid-crustal rocks and rapid cooling suggests the development of a system in which (1) erosion effectively removes material, driving advection of increasingly hotter, weaker rock, forming the gneiss domes which underlie the peaks, and (2) glaciers drive relief production and peak uplift, enhancing orographic precipitation, thus forming larger, more erosive glaciers. 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, measured from field mapping and ASTER imagery as a proxy for relative glacial erosion, we confirm that glacial erosion increases in concert with peak elevations and degree of exhumation. New cosmogenic 10Be data for three locations on the dominant terrace level will constrain the age of the successive moraine deposits and allow a comparison of moraine volume for correlative moraines along the length of the detachment. Age data will also be used to evaluate 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.