Quantitative Studies On Major Active Fault Zones In Northeastern Qinghai-Tibet Plateau

The rise of the Qinghai-Tibet Plateau and the current tectonic activity on it is regarded as the consequence of the collision being in progress between India and Eurasia, Various models and theories to explain the accommodation of the deformation in continent caused by the collision have been proposed, which emphasize different modes of continental deformation. "Crust Thickening" and "Continent Escape" are two most important ones among the models on continental tectonic deformation. North-south shortening induced by the continuous northward push and pressure of the Indian plate is absorbed by two dominant progresses: thrusting and thickening of the crust, responsible for the high topography of the region; and strike-slip faulting, accommodating lateral displacements of continental blocks. Concerning the relative importance during the collision and the proportion in absorbing convergence of the two processes in these two models are still controversial.Quantitative studies of late Quaternary tectonic deformation and slip rates on the main faults in Qinghai-Tibet Plateau and adjacent area is fundamental to understand its kinematic features and dynamic process, and thus essential to help settling the argument mentioned above.1. Microgeomorphology related to the activity of the Western Qinling Fault Zone and Paleo-seismic events along the faultTogether with the Haiyuan and the Kunlun faults, the Western Qinling Fault is one of the main left-lateral strike-slip fault zones in northeastern Tibet, which elongates as one major trace composed of several segments. The fault zone shows dominant sinistral movement, and partly dip-slip component in late Pleistocene. Displacement of the water systems is a widespread phenomenon along the fault zone. The maximum cumulative horizontal displacement of the fault zone is about 300-500m, displacement larger than this is not observed. The maximum horizontal displacement since the late of late-Pleistocene is about 40-70m, and the minimum is 6-8m. 6-8m maybe is the amount of one principal slip associated with one large event. The fault zone behaves differently in segments, and the Wushan fault and the Huangxianggou fault are two main segments of the fault zone. The fault zone has been intensely active since late Pleistocene.The behavior of the fault zone shows typical strike-slip movement at Huangxianggou. Based on the analysis to the gullies across the fault and the related sediments and landforms, and 1/10000 geologic mapping and large-scale relief mapping, we have investigated the stretch of the Huangxianggou segment, the sediments construction, geomorphology, geologic bodies, and the amount of the slip in late Quaternary, etc. The microgeomorphology such as periodic sag-ponding deposition and deforming of pluvial fans is a major feature in the Huangxianggou segment. The sag-ponding depositions were disclosed by 3-D excavation. Based on the analysis to the profile of the stratum and rediocarbon dates of the sediments exposed by the excavation, sediment distribution and characters of the relevant fault were studied, and the relation between the sag-ponding...