地壳增厚与构造逃逸：青藏高原隆升扩展过程中的应变分配及地球动力学控制

The Indo-Asian collision in the past ~50 million years has caused ～2000 km of crustal shortening, which has been accommodated mainly by crustal thickening in the Himalayan–Tibetan Plateau and lateral extrusion of blocks of Asian continents. However, the spatiotemporal evolution of crustal thickening and lateral extrusion, hence the far-field impact of the Indo-Asian collision on Asian tectonics, remains controversial. Here we propose a three-stage investigation of strain partitioning and its geodynamic control during the rise and growth of the Tibetan Plateau. First, we will use GPS and precise leveling data to constrain the present-day crustal deformation and strain partitioning in and around the Tibetan Plateau. Second, we will use viscolastic-plastic finite element models to investigate the geodynamic cause of the present-day strain partitioning, paying special attention to the cause and boundary conditions for strain transformation from crustal extrusion along strike-slip faults to compression near the margins of the Tibetan Plateau. In the final stage, we will extend the geodynamic models, constrained and tested by present-day crustal kinematics, to investigate how changes of the geological and tectonic conditions in the past may have controlled the roles of crustal thickening and tectonic extrusion in the formation of the Tibetan Plateau. Results of this study will have important implications for understanding the fundamental geodynamics of the rise and growth of the Tibetan Plateau, the Cenozoic tectonics of Central and East Asia, and the earthquake hazards in China and surrounding countries.

印度–欧亚板块在过去约5000万年的持续碰撞汇聚造成了近2000公里的地壳缩短，主要由青藏高原的地壳增厚和亚洲大陆块的横向逃逸所分担。然而，地壳增厚和横向逃逸的时空演化，两者之间的动力学联系，以及印-欧大陆碰撞对亚洲构造的远场影响至今充满争议。本项目将对青藏高原隆升生长过程中应变分布及其地球动力学控制做三阶段的研究。首先，我们将使用GPS和精密水准数据来约束青藏高原及邻边地区现今的地壳变形和应变分配。第二，我们将使用粘弹塑性有限元模型来研究现今应变分配的地球动力学原因，特别是沿大型走滑断裂带的逃逸构造和高原边缘地壳挤压缩之间的构造转换。第三，我们将模拟印-欧大陆碰撞，探讨青藏高原形成过程中地壳增厚和构造逃逸的时空演化。这项研究的结果将对理解青藏高原的隆升增长，中、东亚新生代构造，以及中国和周边国家的地震灾害具有重要意义。

本项目从三个方面研究了印度和欧亚大陆碰撞过程中地壳的增厚与横向逃逸。第一，我们结合GPS等空间对地观测数据和地球动力学计算，研究了青藏高原东北缘及东南缘现今地壳的变形，断层的走滑，及区域应变分布。结果表明，沿大型走滑断层的地壳横向逃逸主要局限于青藏高原内部。在青藏高原的边缘，横向逃逸转化成挤压构造。第二，我们利用高精度地球动力学模型计算了在碰撞过程中岩石圈的减薄，包括拆沉和地幔上涌，及其对高原的形成演化的影响。我们的成果表明，大陆碰撞可在青藏高原岩石圈较软弱的地体下造成小尺度的拆沉和地幔上涌，造成新生代晚期的快速隆升。 第三，我们结合地质和地球物理数据，探讨了青藏高原横向扩展的控制因素。我们的成果表明，青藏高原的横向扩展受制于周边亚洲岩石圈的流变性质的控制。在塔里木、鄂尔多斯、和四川盆地等克拉通地块周边，青藏高原没有发生前人模型所显示的那种横向扩张。