Slip rate gradients along the eastern Kunlun fault

Whether strike-slip fault systems in Eurasia accomplish eastward extrusion of Tibetan crust and lithosphere depends largely on the kinematics of deformation at the fault tip. Here we present new slip rate determinations using millennial-scale geomorphic markers from sites along the easternmost segment of the Kunlun fault in north central Tibet. This fault system represents one of the major strike-slip faults within the Indo-Asian collision zone, has been argued to exhibit uniform slip rates along much of its length, and plays a central role in models for eastward extrusion of Tibetan lithosphere. Displaced fluvial terrace risers along tributaries of the Yellow River, coupled with C-14 ages of terrace material, provide constraints on slip rates over late Pleistocene to Holocene time. Results indicate that slip rates decrease systematically along the eastern similar to 150 km of the fault from >10 to <2 mm/yr. These data challenge the view that slip along the Kunlun fault remains uniform along the entire length of the fault and instead reveal gradients in displacement similar to those expected at fault tips. Moreover, slip along the fault appears to terminate within the thickened crust of the plateau, and therefore any extrusion of Tibetan lithosphere accomplished by slip along the Kunlun fault must be absorbed by internal deformation of the plateau surrounding the fault tip.