Be-10 derived basin-wide erosion rates of Southern Qilian Shan, NE Tibet

The actively uplifting Qilian Shan forms the northeastern margin of the Tibetan Plateau. The mountain range is bounded to the northeast by a thrust fault forming a 2 km-high mountain front over the Hexi Corridor basin, and to the southwest by a series of thrusts within an internally-drained elevated plateau that steps downwards into the Qaidam basin. The mountain range forms an important climatic boundary as well, where the East Asian Monsoon gives its way to Northern Hemisphere Westerlies. Understanding the interplay among active faulting, climate, and erosion in this region could be important for revealing the northeastern expansion and uplift of the Tibetan Plateau. Here we present ¹⁰Be derived catchment-wide erosion rates for a large area of the southern Qilian Shan. Our preliminary results show remarkably slow erosion rates ranging from~ 10 - 100 mm/ky,much slower than those reported for rivers draining the north Qilian Shan (ranging from 39-833 mm/ky) [Palumbo et al., 2011]. These results may suggest that catchments draining the mountain front experience relatively high precipitation and are eroding quickly, while catchments in the arid, internally-drained interior are isolated from base level fall and are eroding slowly. Moreover, our erosion rates may also suggest that the interior (southern) portions of the Qilian Shan are deforming more slowly than along the frontal thrust. This is consistent with the North Qilian Shan thrust accommodating most of the tectonic shortening in the mountain range, with shortening occurring at a slower rate in the interior. These data may suggest that low erosion rates (at least partially due to aridity) are promoting surface uplift of the Qilian Shan and Qaidam basin along the northeastern edge of the Tibetan Plateau. Additional samples are being processed from a variety of geologic and climatic settings that we hope will further elucidate patterns of erosion in the Qilian Shan region. Palumbo, L., R. Hetzel, M. Tao, and X. Li (2011), Catchment-wide denudation rates at the margin of NE Tibet from in situ-produced cosmogenic 10Be, Terra Nova, 23(1), 42-48.