青藏高原东北缘海原断裂带晚新生代构造变形  

Late Cenozoic tectonic deformation of the Haiyuan fault zone in the northeastern margin of the Tibetan Plateau

作　　者：王伟涛[1] 张培震[1] 郑德文[1] 庞建章[1] 

机构地区：[1]中国地震局地质研究所地震动力学国家重点实验室,北京100029

出　　处：《地学前缘》2014年第4期266-274,共9页Earth Science Frontiers

基　　金：中国地震局地质研究所基本科研业务专项(IGCEA1127;IGCEA1220);国家自然科学基金项目(41202148;41030317)

摘　　要：海原断裂带是青藏高原东北缘的边界断裂带,其新生代以来丰富的构造变形样式是研究高原向北东方向扩展的天然实验室。采自断裂带上盘南华山的磷灰石裂变径迹热年代学结果、横跨海原断裂带的地震反射剖面分析揭示了海原断裂带晚新生代以来经历了先逆冲、后走滑的两阶段变形过程。海原断裂第一阶段强烈的北东方向逆冲推覆变形始于(12±3)Ma,造成了断裂上盘山体的快速隆升与断裂下盘的挠曲变形,同时,破坏了高原东北缘新生代巨型沉积盆地。海原断裂这种挤压变形代表了青藏高原在约12Ma扩展至现今高原东北部,使其成为高原东北缘的最新组成部分。约5.4Ma,海原断裂第二阶段变形以不断增加的左旋走滑分量为特征,沿断裂带所产生的左旋走滑位移被其尾端的六盘山、马东山以东西向的地壳缩短调节吸收。海原断裂上新世左旋走滑运动,可能主要是青藏高原东北缘北东向挤压变形作用后期高原东北部物质沿其主要边界断裂向东有限挤出的结果。Haiyuan fault zone,which is the boundary fault zone of the northeastern margin of the Tibetan Plateau,provides a laboratory for studying how the plateau has grown northeastward,owing to its plentiful tectonic deformational styles in the Cenozoic time.The analysis results of the apatite fission-track thermochronology from the South Huashan in the hanging-wall of the Haiyuan fault and the seismic reflection sections across the Haiyuan fault zone suggested that the fault had undergone northeastward thrusting with the following left-lateral strike-slip motion since the Late Cenozoic time.In the first phase,the initial northeastern thrusting along the Haiyuan fault occurred at 12±3 Ma and caused rapid uplift of the ranges and flexural subsidence in the hanging-wall and foot-wall of the fault,respectively;at the same time,the thrusting also separated the huge Cenozoic sedimentary basin in the NE margin of the Tibetan Plateau.This event apparently suggested that the outward growth of the Tibetan Plateau had propagated into the present-day NE margin of the plateau and made the Haiyuan fault as the newest part of the plateau since^12 Ma.The second phase deformation along the Haiyuan fault initiated at^5.4 Ma and was characterized by gradual increase in leftlateral strike-slip rate.The component of left-slip displacement along the Haiyuan fault was transferred into eastward crustal shortening in the Liupan Shan and Madong Shan region.This phase of deformation may have resulted from the late period of the northeastward convergence in the NE margin of the Tibetan plateau,which led to the eastward motion of materials in the NE Tibetan Plateau along the main boundary faults.

关 键 词：海原断裂带 构造变形 青藏高原东北缘 

分 类 号：P542[天文地球—构造地质学]