Spatial differences in rock uplift rates inferred from channel steepness indices along the northern flank of the Qilian Mountain,northeast Tibetan Plateau

The rate and distribution of deformation along the Qilian Mountain,on the northeastern Tibetan Plateau,is needed to understand the evolution of high topography associated with the plateau.Recently,a number of empirical studies have provided support for the contention,common to most models of fluvial incision,that rock uplift rate exerts a first-order control on the gradient of longitudinal river profiles.Along the northern Qilian Mountain,this method is used to extract information about the spatial patterns of differential rock uplift.Analysis of the longitudinal profiles of bedrock channels reveals systematic differences in the channel steepness index along the trend of the frontal ranges.Local comparisons of channel steepness reveal that lithology and precipitation have limited influence on channel steepness.Similarly,there is little evidence suggesting that channel steepness is influenced by differences in the sediment loads.We argue that the distribution of channel steepness in the Qilian Mountain is mostly the result of differential rates of rock uplift.Thus,channel steepness indices reveal a lower rock uplift rate in the eastern portion of the Qilian Mountain and a higher rate in the middle and west.The highest rates appear to occur in the middle-west portions of the range,just to the west of the Yumu Shan.