3-D Numerical Modeling Analysis Of The Rotation Deformation Mechanism Of The Southeastern Margin Of The Tibetan Plateau

During the subduction of the Indian plate to the Eurasian plate and with the obstruction of the North China block,the material of the eastern Qinghai-Tibet Plateau is subjected to eastward squeezing.At the same time,under the obstruction of the South China block in the east,the material in the southeastern margin of the plateau began to "escape" southward and showed the kinematic characteristics of clockwise rotation.In order to study the above dynamics,dynamical models in 2-D elasticity,viscoelasticity and 3-D viscoelasticity are constructed by Finite Element Method for the Southeastern Qinghai-Tibet Plateau,on the base of measurements of the GPS velocity,focal mechanism and in-situ stress,regional tectonic division and structures in the southeastern margin of the Qinghai-Tibet Plateau and the surrounding blocks.,,The distribution of tectonic stress field and the dynamic mechanism of the deformation in the southeastern margin of the Qinghai-Tibet Plateau are investigated by considering to the GPS velocity field,the focal mechanism solution and the measured stress field.The displacement field obtained by numerical simulation is basically consistent with the material motion measurement by GPS.From the overall movement trend,the material movement in the southeastern margin of the Qinghai-Tibet Plateau shows clockwise rotation,i.e.,is characterized by the NE or NNE movement in the northern part,SE or SSE in the central part,and SW in the southern part.The maximum principal stress of the Sichuan-Yunnan block in the southeastern margin of the Qinghai-Tibet Plateau is characterized by fan-shaped expansion around the Himalayan tectonic structure.The direction of the maximum principal(compressive)stress is rotated clockwisely from NE or NNE in the northern part to SE or SSE in the southern part.The maximum principal stress of the South China plate in the southern section of the North-South Seismic Zone is along the direction S-N.The distribution characteristics of the tectonic stress field simulated in this dissertation are basically consistent with the focal mechanism solution and the stresses obtained by in-situ stress measurements.The dynamic mechanism of the southeastern margin of the Qinghai-Tibet Plateau is related with the subduction of the Indian plate to the Eurasian plate,the pulling effect of the Myanmar plate on the Sunda plate,the stretching effect of the Philippine plate to the eastward movement,the blocking action from the North China block and the South China block,and the dragging action of the upper mantle and the lower crust.Under the combined action of the above mechanisms,the northwestern part of the Sichuan-Yunnan block and the Malcolm block are in the crushing environment,the Xianshuihe-Xiaojiang fault zone,the Longmenshan fault zone and the Kunlunshan fault zone Showing the characteristics of the strike-slip movement;the central and southern Yunnan regions show the tensile environment,the Red River fault zone south of the performance of the strike-slip characteristics,the real fault zone showed near-north-south strike slip characteristics.