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

摘要： 通过分析中国地壳运动观测网络的GPS数据得到川滇地区地壳水平运动速度场,由此划分活动块体并分析其运动特征。结果表明:相对欧亚板块,滇中、雅江和中甸次级块体的顺时针转动速率分别为0.37°±0.16°/Ma,0.84°±0.39°/Ma和0.90°±0.39°/Ma,造成块体间跨木里弧形断裂带约3mm/a的SN向挤压、丽江-大理断裂带约4mm/a的EW向拉张和理塘断裂带约6mm/a的近EW向拉张。鲜水河断裂带左旋走滑速率8～10mm/a,安宁河-则木河-小江断裂带左旋走滑5～6mm/a。龙门山断裂带没有明显的地壳消减,而断裂带西北约150km处有一形变速度阶跃带,右旋走滑速率4～5mm/a。阶跃带两侧的岷山块体和阿坝地区逆时针转动速率分别为0.13°±0.08°/Ma和0.53°±0.19°/Ma。鲜水河-小江断裂带以南、以西地区,青藏高原物质的E向挤出和重力滑塌造成川滇块体东移,在东部相对稳定的华南地块的阻挡下,川滇块体沿鲜水河-小江断裂带由东转向南运动,从而引起川滇块体内部各次级块体的顺时针转动。

关键词: 川滇地区, 地壳形变, GPS, 活动块体