Active Tectonics of the Longmen Shan Region on the Eastern Margin of the Tibetan Plateau

There is a massive amount of geomorphic evidence for active tectonics in the Longmen Shan at the eastern margin of the Tibetan plateau.We have surveyed some typical geomorphic markers including the Wenchuan-Maowen,Beichuan-Yingxiu and Pengxian-Guanxian faults,terrace offsets, scarps,fault-controlled saddles,dextral shutter ridges,dextral channel offsets,graben,shatter belts, and pull-apart basins.Electron spin resonance(ESR) and thermoluminescence(TL) ages were obtained using silty sand taken from below the surface of the sediments.According to these data,we calculated the rates of thrusting and strike-slip,and the results indicate that Cenozoic tectonic shortening at the plateau margin is minor with the rate of thrusting less than 1.10 mm/a and the rate of strike-slipping less than 1.46 mm/a.The Longmen Shan is a zone of NNE-trending dextral shear with slip-dip ratio of 6:1-1.3:1.From NW to SE,the thrust component becomes smaller,whereas the strike-slip component becomes larger.