青藏高原东北缘六盘山构造带及邻域的动力学响应数值模拟

Numerical simulation on the dynamic response of Liupanshan tectonic belt in the northeastern Tibetan Plateau and its adjacent regions

青藏高原东北缘地区是青藏高原向北东方向扩展的前缘部位,也是探索青藏高原深层动力过程的重点区域.本文基于该区已有的地球物理探测工作,构建了横跨青藏高原东北部块体、六盘山构造带和鄂尔多斯盆地的二维剖面的数值模型,采用黏弹性数值模型对竖直向重力场展布对其构造演化过程及动力学响应进行了探讨.研究结果表明:(1)深部竖直向异常重力场特征导致了复杂的垂向动力学响应变化,造成了深部物质的复杂运移,而印度板块向北运动的挤压推力依然是青藏高原东北部—鄂尔多斯盆地深部动力学响应的主导因素.(2)流变结构及应变能的计算结果证明,在六盘山构造带地壳内能量最为聚集的地方与海原地震的深度大致相当,而青藏高原东北部地域与六盘山构造带的物性结构、形变速率、升降幅度等方面的差异,亦是造成低速层边界岩石破裂,且导致海原强震发生的主要原因.(3)在青藏高原东北部—鄂尔多斯构造区域的特异流变性结构,并不利于下地壳物质的流动.

The northeastern Tibetan Plateau is the leading-edge of the Tibetan Plateau extension to the NE direction. Also,it is one of the key regions to explore the deep dynamical process of the Tibetan Plateau. Based on the pre-existing geophysical exploration in the research area, numerical model has been constructed. In this paper,2-D Finite Element Method is used with viscoelastic model to simulate the tectonic evolution process and the dynamic response of the vertical gravity field distribution through the profile across the northeastern Tibetan Plateau,Liupanshan tectonic belt and Ordos basin. The results shows that：（1） The deep vertical abnormal characteristics of gravitational field resulted in the complicated vertical dynamic response,which caused the complex migration of the deep material. The thrust force of the northward movement of the India plate is still the dominant factor of the deep dynamic response in the northeastern Tibetan-Ordos basin.（2） The distribution of the strain energy,the rheological structure and other results are calculated numerically,which show that the sections with energy concentration roughly the same as the depth of the Haiyuan earthquake. There are differences in the physical structure,deformation rate, heave amplitude of the northeastern Tibetan Plateau and Liupanshan tectonic belt. Which is resulted in the rock rupture in the low velocity layer boundary,and the major cause of the Haiyuan earthquake.（3） The specific rheological structure of the northeastern Tibetan Plateau and Ordos basin is not favorable for the movement of the low crustal material.