Recent deformation and displacement of continental lithosphere in the northeastern margin of Qinghai - Tibet Plateau

The Sichuan-Qinghai block, which is geomorphologicaUy the Westem Sichuan Plateau, is the most important tectonic unit on the northeastern margin of the Qinghai-Tibet Plateau. New GPS monitoring data indicate that in the Eurasian flame, the horizontal velocity of the crustal movement in the Sichuan-Qinghai block and its adjacent Longmen Mountain belt and the western margin of the South China block shows a general trend of decreasing progressively from 25.66 to 6.99 mm/a from west to east. The velocity vector shows a clockwise vortex rotation. A regional inhomogeneous shear field with local accumulation of strains occurs within the Sichuan-Qinghai block. The new GPS data along a profile across the central segment of the Xianshuihe fault belt reveal that the average left-lateral slip rate between blocks on both sides of the segment is -8 mm/a. The GPS data also indicate that owing to local accumulation of strains the left-lateral slip motion rate of the main fault along the southwestern margin of the fault system is 9.3 mm/a. Between the two faults, there are a pull-apart basin and a minor transverse extensional fault. The left-lateral slip motion of the Xianshuihe fault system accommodates the relative motion between the Sichuan-Qinghai block and the Sichuan-Yunnan block.