A RECORD OF EROSION OF THE INTERIOR EASTERN TIBETAN PLATEAU HIGHLAND FROM DETRITAL THERMOCHRONOLOGY

River incision histories from the externally drained headwaters of the eastern Tibetan Plateau should reflect topographic change and regional climate events and thus provide insight into the much-debated evolution of the Tibetan orogen. In this study, detrital low-temperature thermochronology of modern river sand reveals the geomorphic development of this region and provides a useful comparison to erosion rates from the internally drained central plateau, the eastern plateau perimeter and the record of sedimentation from offshore fans. Individual apatite grains from eight drainage basins that stretch S-N across the plateau yield a range in (U-Th)/He and fission track ages that, in most cases, span the Cenozoic and late Mesozoic eras. Such wide distributions require a prolonged interval of slow erosion in order to preserve the older ages followed by a relatively recent rate increase to account for ages as young as Pleistocene. Inverse model results show that an increase in erosion rate by at least an order of magnitude occurred between 11 and 4 Ma following a long period of slow erosion. Increased erosion began in concert with a similar rise in rate along the eastern plateau flanks. Erosion intensification also overlaps with or follows soon after initiation of several major E-W strike-slip faults and a change in deformation style along the NE Tibet margin. Taken together, synchronous accelerated river incision and changes in faulting across such a broad area likely related to the eastward expansion of an already thick and high southern and central plateau late in the orogen’s history. Changes in climate, for example a stronger monsoon system, may have accompanied regional deformation in driving the higher erosion rates. These results provide a context for the offshore sedimentation records that have also been interpreted to relate to the timing of monsoon system strengthening and regional rock uplift.