Erosion history of the Tibetan Plateau since the last interglacial: constraints from the first studies of cosmogenic Be-10 from Tibetan bedrock

The cosmogenic Be-10 exposure histories of in situ bedrock surfaces from the Tibetan Plateau indicate low erosion rates of <30 mm/ka in southern and central Tibet during the last interglacial-glacial cycle that contrast strongly with unusually rapid erosion rates (60-2000 mm/ka) for Kunlun in northern Tibet during the Holocene, comparable with published values from the Himalaya. By comparing apatite fission-track ages with cosmogenic data, erosion rates in southern Tibet appear to be decelerating since the Miocene, whereas in the Kunlun, erosion rates have accelerated over the same timescale. Such secular changes suggest that the southern and central regions of the plateau had formed their present flat relief by the Pleistocene. Unusually high erosion rates along the northern margin of the plateau may reflect intense tectonic activity during the Holocene. These findings indicate that over much of the high plateau erosion rates are exceptionally low, and therefore the sources of detritus carried by the great Asian rivers that rise in Tibet lie overwhelmingly in bedrocks at lower altitudes. This study illustrates the potential of cosmogenic studies for unraveling the most recent phase of the erosion/exhumation history of orogenic belts that cannot be resolved by either Ar-isotope or fission-track thermochronometers. (C) 2003 Elsevier B.V. All rights reserved.