鄂尔多斯南缘构造带现今地块运动模式

依据研究区内断裂体系及GPS地体运动矢量数据,将鄂尔多斯南缘构造带分割成AK共11个断块群,将差异性GPS数据转化为断块之间的细部相对运动,给研究地块细部运动差异提供一种全新的研究思路与研究模式。鄂尔多斯南缘中东部现今构造应力场整体为挤压应力环境。在渭河盆地西部,从西南方向中秦岭动力楔传递而来的挤压应力峰点在武功咸阳口镇一带形成应力主轴,应力主轴两侧楔形地块普遍存在侧向挤出逃逸,逃逸使GPS运动矢量偏离区域主应力方向。渭河盆地东部则存在左行走滑,显示出豫西断隆的阻隔碰撞作用。鄂尔多斯南缘现今地块相对运动规律符合"三头碰撞"模式,四川地块、鄂尔多斯地块、豫西断隆三个地块的"三头碰撞"形成高应力区,"头间逃逸带"形成走滑带和相对低应力区。本次提出地体之间的"多头碰撞"和"头间逃逸"构造模式有一定的普遍性,研究清楚地块之间哪里是"头"接触点、哪里是"头间逃逸带",可以成为研究大中地块周围震源机制分布规律的有效途径。

Ordos Block Modern Movement Patterns in Southern Ordos Margin Tectonic Belt

Southern Ordos block were divided into 1 1 irregular sub-groups from A to K in terms of the newly observed GPS data through converting the different GPS data into the detail relative motion between the blocks.The authors provide a new idea and model for studying the detailed movement differences based on these different GPS data.The present stress field is compressive in east and central parts of southern Ordos.The compressive stress comes from the southwest Qinling power wedge which is a compressive stress peak.The compressive stress peaks make up the Wugong Xianyang Kouzhen Line a stress axis,and then those shape-wedged blocks,that are standing both sides of the stress axes, are all laterally extruding and escaping in the western Weihe basin.The escaping blocks make some GPS motion vectors deviate off the main motion direction.There is a wide sinistral strike-slip in the eastern Weihe basin,which can show action of blocking and collision of western Henan uplift.The shape-wedged blocks were extruded laterally,which complicate the GPS vector data.The pattern of relative movement of these blocks complies with a “three head collision”tectonic model in southern Ordos. Based on this model,collision among Sichuan block,Ordos block,and Yuxi block resulted in stress concentration,and these blocks were then laterally extruded along the strike-slip faults developed in low stress region.The authors present a “multi-head collision”and “escape between heads”model which has a certain universality.It will be an effective way to figure out where are the “head”contact point and where are the “escape between heads”for study the focal mechanism distribution around some large or medium blocks.