祁连造山带地壳—上地幔顶部三维速度结构及其意义

发布时间：2018-01-25 01:11

  本文关键词： 祁连造山带 地震层析成像 速度结构 下地壳塑性流动 壳内地震　出处：《西北大学》2017年硕士论文　论文类型：学位论文

【摘要】：祁连造山带作为青藏高原东北缘的重要组成部分,其详细的地壳-上地幔顶部三维结构特征对探讨青藏高原东北缘新生代变形机制、祁连造山带与华北板块深部构造关系、以及该区内壳内大地震的诱发机制都具有非常重要的意义。本论文使用研究区内分布的72个固定台站在2009年到2015年间记录到的7485个地震事件,包括75999个P波到时数据和72178个S波到时数据,利用天然地震层析成像方法获得了祁连造山带地壳-上地幔顶部详细的三维P、S波速度结构。结果表明,祁连造山带地壳-上地幔顶部三维速度结构具有显著的纵/横向不均一性。地壳浅部速度结构特征与地表地质特征基本一致,总体表现为高、低速的分布与山脉和盆地的分布相对应。祁连构造带下地壳内广泛发育低速异常带,局部地区延伸至上地幔顶部。结合该区其他地球物理资料,认为该低速异常区代表了下地壳中因流体和部分熔融体存在而造成的弱化带,其很可能与青藏高原的隆升与变形及其向北扩展以及局部地区上地幔物质上涌有关。祁连造山带下地壳的弱化可使其在地质历史时间尺度发生塑性流动,而低速异常带的分布表明,塑性流动的规模并不很大。北祁连和走廊过渡带地壳底部以及上地幔顶部内存在明显的高速异常,该高速异常可能代表了向祁连造山带下方俯冲的阿拉善地块的岩石圈,该俯冲作用很可能与新生代印度板块和欧亚板块的俯冲碰撞过程有关。研究区内的壳内大地震大多数都分布于区域内的大型断裂带上,震源区位于高、低速异常过渡带,震源区下方存在广泛的低速异常区。结果表明大地震的发生是断裂、应力以及流体综合作用的结果,并且与下地壳以及上地幔顶部的动力学过程紧密相关。综上所述,祁连造山带甚至是整个青藏高原东北缘新生代的变形,可能并非是某种单一机制作用的结果,而是大陆岩石圈俯冲、下地壳塑性流动以及上地幔物质上涌多种机制于不同时段、不同区段共同作用的结果。
[Abstract]:The Qilian orogenic belt is an important part of the northeastern margin of the Qinghai-Xizang Plateau, and its detailed three-dimensional structure of the crust and upper mantle is discussed in the Cenozoic deformation mechanism of the northeastern margin of the Qinghai-Xizang Plateau. The Qilian orogenic belt is related to the deep tectonics of the North China plate. The induced mechanism of large earthquakes in the inner crust of this area is of great significance. In this paper, 7485 earthquake events recorded by 72 fixed stations in the study area were recorded between 2009 and 2015. The piece. Including 75999 P-wave time data and 72178 S-wave arrival data, the detailed 3D P values of the crust and upper mantle of the Qilian orogenic belt are obtained by using natural seismic tomography. The results show that the 3D velocity structure of the crust and the upper mantle of the Qilian orogenic belt has obvious longitudinal / lateral heterogeneity, and the velocity structure of the shallow crust is basically consistent with the geological features of the surface. The distribution of high and low velocity corresponds to the distribution of mountains and basins. In the lower crust of the Qilian tectonic belt, a low velocity anomaly zone is widely developed, and the local area extends to the top of the upper mantle, combining with other geophysical data in the area. It is considered that the low velocity anomaly represents the weakening zone in the lower crust caused by the presence of fluids and partially molten bodies. It may be related to the uplift and deformation of the Qinghai-Xizang Plateau and its northward extension, as well as the upwelling of the upper mantle material in some areas. The weakening of the lower crust of the Qilian orogenic belt can make the ductile flow take place on the time scale of geological history. The distribution of low velocity anomaly shows that the scale of plastic flow is not very large. There are obvious high speed anomalies in the crust bottom and upper mantle top of North Qilian and Corridor transition Zone. The high velocity anomaly may represent the lithosphere of the Alashan block subducting to the Qilian orogenic belt. The subduction is probably related to the subduction and collision process of the Cenozoic Indian plate and Eurasian plate. Most of the large earthquakes in the crust in the study area are located on the large fault zone of the region and the focal area is high. In the transition zone of low velocity anomaly, there is a wide range of low velocity anomaly areas below the focal area. The results show that the occurrence of large earthquakes is the result of the combined action of faults, stresses and fluids. In conclusion, the Qilian orogenic belt and even the Cenozoic deformation of the northeastern margin of the Qinghai-Tibet Plateau may not be the result of a single mechanism. It is the result of the subduction of continental lithosphere, the plastic flow of the lower crust and the upwelling of the upper mantle material.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P315.2
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本文编号：1461563