青藏高原东缘旋转变形机制的数值模拟
Numerical modeling analysis of the rotation deformation mechanism of the eastern margin of the Tibetan Plateau
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摘要: 在印度板块与欧亚板块的碰撞作用下，青藏高原受到华南块体、鄂尔多斯块体等不同程度的阻挡，引起高原的整体隆升。青藏高原东南缘发生物质向南“逃逸”，青藏高原东缘现今的地壳运动表现为围绕青藏高原东构造结发生顺时针的旋转。针对青藏高原东缘的旋转变形特征，基于以大型活动断裂为界的块体构造模型，利用粘弹性接触单元有限元模拟，分析了控制青藏高原东缘旋转变形的动力学环境，模拟的GPS速度与实测GPS速度能够较好的地吻合，构造应力场分布特征和活动断层的性质也能够较大程度地吻合，模拟过程采用的边界及其代表的动力学环境表明，青藏高原东缘整体受控于印度板块的持续碰撞和稳定的华南板块的阻挡，在下地壳的拖曳和重力作用下，青藏高原物质从南部边界“逃逸”。在“逃逸”过程中，受印度板块斜向俯冲作用的影响，沿实皆断裂缅甸板块对巽他板块的剪切拉升作用是形成围绕喜马拉雅东构造结的旋转运动和地壳变形的重要因素，也是青藏高原东南缘旋转活动构造体系的主要影响因素之一。Abstract: The Tibetan uplift is controlled by the continuous collision of Indian plate and Euro-Asia plate as well as South China block and Ordos block. The materials on the southeast margin of the Tibetan Plateau escaped southward. The crustal motion of eastern Tibet indicates the clockwise rotation around the eastern Himalayan syntaxis. Making use of the contact element viscoelastic finite element (FE) method, the authors analyzed the mechanism of the rotation of the eastern margin of the Tibetan plateau. The FE model simulated the geological block structure which is bounded by large active faults. The simulated GPS accords well with the measured GPS, and the tectonic stress state coincides well with the property of active faults. The boundary conditions of FE modeling show that the material escape of southeastern Tibetan Plateau resulted from the lower crust dragging and the gravity influence, that during the southward escape the shear extension dragging along the sagging fault induced by oblique subduction of India plate under the Myanmar plate caused the rotation of eastern Tibetan Plateau around the eastern Himalayan syntaxis, and influenced the active structural system of southeastern Tibetan plateau.
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