青藏高原东北缘祁连山中部精细地壳结构研究

Disclosure of high-resolution crustal structure beneath the central region of Qilian Shan,northeastern Tibetan Plateau

现今的青藏高原东北缘祁连山地区是在早古生代构造格架的基础之上,于新生代在欧亚大陆与印度大陆碰撞拼合的远程影响下,重新活化进而隆起成为高原的组成部分.因此,该区域地壳结构的揭示不仅可以获得高原地壳变形方式的关键信息,而且也能对该区域早古生代晚期北祁连洋闭合时的相关构造演化提供重要证据.本文以一条穿过青藏高原东北缘祁连山中部地区的深地震反射剖面为基础,结合前人地质、地球物理资料,通过细致的地质构造解译,获得了青藏高原东北缘祁连山中部地区的精细地壳结构.反射剖面图像揭示了海原断裂西段的深部延伸形态、中地壳的双重构造、以及中下地壳的祁连逆冲断裂系等精细的深部构造.结合前人的地质以及地球物理资料,我们提出早古生代晚期北祁连闭合时的南向俯冲以及新生代以来祁连山地区两次陆内俯冲作用可能造就了现今的祁连山.

The formation of present Qilian Shan in the northeastern margin of the Tibetan Plateau(NE Tibetan Plateau)is based on the tectonic framework resulted from the closure of the North Qilian Ocean during the late Early Paleozoic.Under the far-field influence of the collision between the Eurasian and Indian continents in the Cenozoic,the Qilian Shan was reactivated and uplifted to become a part of the plateau.Therefore,the revelation of crustal structure in this region can not only obtain key information about the deformation mechanisms of the plateau crust,but also provide important evidence for the tectonic evolution related to the late Early Paleozoic in this region.Based on a deep seismic reflection profile passing through the middle Qilian Shan area in the NE Tibetan Plateau,the fine crustal structure of this area has been obtained through careful interpretation of geological structure by combining previous geological and geophysical data.The reflection profile image reveals the deep morphology of the western segment of the Haiyuan fault,the duplex structure of the middle crust,and the Qilian Shan thrust system of the middle and lower crust.Based on this,we propose that southward subduction has occurred during the closure of the North Qilian Ocean,and the present Qilian Shan was formed by two intracontinental subductions since the Cenozoic.