Abstract: Based on the available geological and geophysical evidences as well as the geodyna-mics of basin and range structure, the current deformation and stress state in a simplified tectonic profile crossing northeasternly the Xizang plateau, about 2,000km long and 80 km deep, have been analysed using finite element method. Numerical results show that the Indian plate motion is the driving force to disturb the gravity equilibrium leading to a lateral density contrast, but the horizontal compression resulting from the isostatic adjustment is the mechanism for plateau uplift and earthquake development, and that stresses often concentrate at the main fault ends near the low velocity layer.Electrical conductivity measurements of 2-mica gneiss under temperature and pressure conditions equivalent to about 40km deep, together with the optical determination and the X-ray diffraction analysis, indicate that the mechanical weakening due to the dehydration, accompanied with lattice breaking of muscovite and the thermal cracking of quartz may be the mechanisms of forming the low velocity-low resistivity layer in the plateau crust, but the shear movement existing along the low velocity layer seems to be the source of raising its temperature.

摘要： 根据现有的地质和地球物理资料以及山区和平原的动力学观点,利用青藏高原北东向的简化构造剖面(全长约2000公里,深约80公里),对其当前的形变和应力状态进行了有限单元分析。数值结果表明,印度板块运动是扰动重力均衡和导致侧向密度差异的驱动力,但是由于均衡调整所产生的水平压应力才是高原上升和发生大地震的机制;还表明应力集中的必备条件是主要断裂带的端部接近而不穿过低速层。 在相当于40公里深度的温度、压力条件下,二云母片麻岩的电导率测定,簿片鉴定和X光分析等都证实,由于白云母脱水所伴随的晶格破坏以及石英的热裂作用所造成的力学性质的弱化似是高原地壳低速层的形成机制,但是沿低速层的剪切运动则是增高这层温度的重要来源。