Late Quaternary slip rate and kinematics of the Baoertu Fault, constrained by 10Be exposure ages of displaced surfaces within eastern Tien Shan

Investigation on the kinematics and deformation rates about active fault interior of the Tien Shan can provide significant information for strengthening our understanding on the present tectonic evolution of this range. The Baoertu Fault (BETF) is a major E-W striking active structure within the eastern Tien Shan and separates the south and central Tien Shan. But its kinematics and slip rates in the late Quaternary have never been systematically reported before. Based on interpretations of remote sensing images, drone photography, and detailed field investigations, we propose that the BETF is characterized by left-lateral strike-slip faulting with a thrust component and provides the first late Pleistocene slip rate for this fault. At the northern margin of the Kumishi Basin, combining offset reconstructions of displaced alluvial fan surfaces with the terrestrial cosmogenic nuclide (TCN) exposure age dating, we calculate an average sinistral slip rate of 0.65±0.16 mm/yr and average vertical slip rate of 0.07±0.01 mm/yr for the BETF since 95-106 ka. The differential movement eastward between the central Tien Shan block and Yanqi-Kumishi Basin block is likely the dominant driver of the left-lateral slip of the BETF. Synthesizing other quantitative data in eastern Tien Shan, we suggest that the hinterland active faults or folds, including the BEFT, roughly accommodate ∼28-45% of the total N-S convergence across the eastern Tien Shan.