蒙古-贝加尔裂谷区深部结构研究进展综述

Review of deep structure research progress in Mongolia Baikal rift zone

针对蒙古-贝加尔裂谷形成的动力机制和演化过程的两种观点,本文整理了近年来蒙古-贝加尔裂谷活动构造、重力异常、层析成像及接受函数等方面的研究成果,分析蒙古-贝加尔地区深层介质尤其是上地幔的各向异性特性,探究深部物质的变形方式和流动模式,探讨了蒙古-贝加尔裂谷形成和演化的条件.结果表明,蒙古-贝加尔地区地幔流场及对流应力场呈现非常复杂的图像,流场及应力场分布与地表构造具有很好的相关性.蒙古-贝加尔裂谷系的形成不是单纯的构造伸展或壳下岩石圈被热的软流圈物质机械代替的过分简单的模式,而是裂谷系的岩石圈强烈地构造热活化,即有软流圈上隆,熔体侵入.在蒙古-贝加尔裂谷形成和演化中地幔柱发挥了重要作用,同时与线性岩石圈年代及其相对于地幔柱位置有关,也与India-Asia碰撞提供的有利的远场力相关,这三者构成了蒙古-贝加尔裂谷形成和演化的三个条件.

This paper sorts the results of active tectonic structure,gravity anomaly,tomography and so on in Baikal rift valley in recent years,for the two views of the mechanism formation and evolution in Baikal rift and analyzes deep medium especially the anisotropic characteristics of the upper mantle,exploring deep material deformation mode and flow pattern in this region.The results show that mantle flow field and mantle convection stress field are very complicated,the flow field and stress field have a good correlation with the surface structure.The formation of Baikal rift is not a simplistic model which a pure lithosphere extension or subcrustal lithosphere is instead by hot asthenosphere material,but it is the lithosphere strongly tectonic thermal activation, which asthenosphere is uplift upwards.The main reason of Baikal rift system is the mantle uplift,but remote effect of India-Asia collision caused by the lithosphere extension also plays a role.The scientist use a large number of high-quality arrival time data collected from teleseismic events recorded by a dense portable seismic network to invert the velocity structure of the upper mantle beneath the Baikal rift zone.The results reveal that Low-velocity anomalies in the upper mantle are existence under the Baikal rift zone,and a high-velocity anomaly having a thickness of 150~180km in the lithosphere of the stable Siberian craton is interpreted as strong lateral heterogeneity exists in the lithosphere of the Mongolian fold belt.It was suggested that mantle plume has played an important role in the formation and evolution in Mongolia-Baikal rift,and at the same time related to the position of linear lithosphere relative to the mantle plume,also with the relevant to collisions with India-Asia also provide favorable far field,these constitute three conditions of the Mongolia-Baikal rift formation and evolution.