关键词: 川滇地区, 地壳形变, GPS, 活动块体

Abstract: We derive horizontal velocity field of the Sichuan-Yunnan region by analyzing GPS data collected from the Crustal Movement Observation Network of China between 1998 and 2001. Our result shows that the region is composed of 4 tectonic terrains: the Chuan-Dian block, the Longmen Shan region, the Red River shear zone, and the Ruili Ximeng region. The Chuan-Dian block is further decomposed into 3 sub-blocks: the Dianzhong block, Yajiang block and Zhongdian block. The Longmen Shan region is decomposed into the Minshan block and the Aba region. Viewed relative to the Eurasian plate, the Dianzhong block, Yajiang block and Zhongdian block are rotating clockwise at 0.37°±0.16°/Ma, 0.84°±0.39°/Ma and 0.90°±0.39°/Ma, respectively, resulting in active faulting between the sub-blocks: ～3 mm/yr north-south shortening across the Muliarcuate Fault, ～4 mm/a east-west extension across the Lijiang Fault, and ～6mm/a east-west extension across the Litang Fault. About 8～10mm/a left-lateral strike-slip is detected across the Xianshuihe Fault, and 5～6mm/a left-lateral strike-slip across the Anninghe-Zemuhe-Xiaojiang Fault. No obvious crustal shortening is observed across the Longmen Shan Fault. About 150km northwest of the Longmen Shan Fault lies a velocity gradient zone with a 4～5mm/a right-slip across. The Minshan block and the Aba region bounded by the gradient zone rotate counterclockwise at 0.13°±0.08°/Ma and 0.53°±0.19°/Ma relative to the Eurasian plate, respectively. Our results are consistent with a model attributing the crustal deformation of the Chuan Dian block in the Sichuan Yunnan region to be driven mainly by the eastward extrusion and gravitational collapse of the Tibetan Plateau. Being resisted by the relatively stable south China block to the east, the Chuan-Dian block turns from eastward to southward motion along the Xianshuihe-Xiaojiang Fault, resulting in a cluster of clockwise rotations of its internal sub-blocks.

Key words: GPS, Sichuan-Yunnan region, crustal deformation, active tectonic block