The Qilian （祁连） Mountain is an active orogenic belt located at the northeastern margin of the Tibetan Plateau. During the process of continuous convergence between Indian and Eurasian plates, the Qilian Mountain grow correspondingly by means of reaction of old faults and generation of new ones. Here we present apatite fission-track data along a river profile crossing three minor fault （the Minle （民乐）-Damaying （大马营） fault, the Huangcheng （皇城）-Taerzhuang （塔尔庄） fault and the Kangningqiao （唐宁桥） fault） which compose the North Qilian fault （NQF） to test the timing and pat- terns of the fault activities. Apatite fission-track （AFT） results indicate that these minor faults expe- rienced two active phases in the Cretaceous and the Oligocene-Miocene. Further research indicate that the initiation timing of faulting became younger northward in both active periods and the later phase probably more active than the former phase. These tectonic activities might be highly related to the docking of the Lhasa Block to the south in the Cretaceous and uplift and expansion of the Tibetan Pla- teau in the Cenozoic.
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.
HU XlaoFeiPAN BaoTianKIRBY EricLI QingYangGENG HaoPengCHEN JiFeng
