柴达木-祁连山地块内部震间上地壳块体运动特征与变形模式研究

以青藏高原北缘及东北缘的柴达木-祁连山地块内的活动断裂、由断裂所围限的微小块体为研究对象,系统收集整理区内活动断裂定量参数和GPS速度场等资料,使用球面应变率计算方法分析研究区内GPS 速度场得到现今构造应变率场,讨论区内最大剪应变率、面膨胀率与旋转率等参数与区域构造变形之间的关系;同时,依据区内详实的活动断裂资料建立精细的微小活动块体模型,利用Backslip模型反演断裂所围限的各个块体边界断裂的滑动速率、块体内部统一应变率及块体欧拉运动学参数等,并与活动构造方法获得的滑动速率做对比;最后,讨论研究区内由GPS速度场所揭示的地壳运动变形模式.结果表明:(1)柴达木-祁连山地区地壳运动,在沿着山脉走向上具有带状区域分块运动特征,大范围内具有弥散变形特征;(2)青藏高原北部变形场应是通过不同断裂差异性相对运动、区域内部逆冲挤压和块体旋转共同作用的结果.从鄂拉山到古浪民勤一带具有强烈的逆冲活动,其两侧地壳块体分别具有逆向旋转的运动性质;(3)在研究区东部GPS速度场所呈现顺时针旋转的形态,应是处于不同地块边界处的中下地壳与地幔介质差异驱动机制对上地壳块体所产生的作用,并以近地表断层应变率积累形式表现的结果,是祁连山地块、阿拉善块体、鄂尔多斯地块等大型块体推挤旋转影响下的复杂运动学形态.

Intersiesmic kinematics and defromation patterns on the upper crust of Qaidam-Qilianshan block

We discuss the strain rate fields and micro block models using the GPS velocity field in the Northern and Northeastern Tibetan Plateau based on active faults distribution and GPS velocity field. We calculate the tectonic strain rate fields using a spherical wavelet-based multi-scale approach for estimating the spatial velocity field on the sphere from a set of geodetic displacement observations. The calculated results including the spatial gradient tensor quantities such as dilatation rate, strain rate and rotation rate could be used to discuss the regional tectonic environment. We also adopt the block model approach with Backslip model to establish a small spatial scale micro-block model, which is used to invert for the slip rates of active faults and compared with geological slip rates, as well as the uniform strain rates in blocks and Euler poles for each block. As a result, we consider that: (1) Crustal deformation along the Qilian Shan range possesses the motion characteristics of blocks with narrow belt shapes in NE direction. (2)Contemporary deformation fields of the Northern Tibetan Plateau should be the result of combined actions of the relative movement of active faults' two sides, thrust and extrusion of the thrust faults and micro-blocks rotation bounded by the principal and secondary active faults in the region.(3) Rotation state of GPS velocity field in the east of the region near Lanzhou and Tianshui has been the result of systematic differences in regional lithosphere structure which affects the driving mechanisms of smaller crustal blocks deformation consequently.