鄂尔多斯地块西部南北向拆离滑覆构造

鄂尔多斯地块西部东西向的推覆构造及基底拆离现象已有较多的讨论和研究.对重力作用下的南北向基底拆离滑覆现象还未见讨论.以地震反射特征的明显差异为依据,结合区域地质特征,研究了鄂尔多斯地块西部南北向基底拆离形成的韦州-石沟驿拆离滑覆构造.它在地震剖面上表现为:滑脱面以上的多层平行反射、不出现逆冲推覆前缘带复杂变形造成的杂乱反射;平面上形成与周邻明显的构造不协调性.韦州-石沟驿拆离滑覆构造形成于晚侏罗世地块西部大规模的东西向逆冲推覆造成的南高北低的构造背景下,在重力作用下由南至北沿T9界面附近的煤系地层拆离滑覆,在东、西、北均以断层与周邻相接,为一外来岩席构成的复式向斜,构造变形相对简单.本研究对该区的构造演化研究及油气勘探具有一定的启示意义.

South-north trending detachment structures in the western ordos block

South-north trending detachment structures in the basement of the western ordos block have not been documented yet though both of the east-west trending thrust and the basement detachment structures in the western ordos block were well studied. On the basis of distinct reflection features in the seismic section and the relevant geological setting it is revealed that the Weizhou-Shigouyi detachment structure, as the result of the northward decollement of the western ordos block, exhibits multi-layer reflection above the detachment surface and there is a scarcity of chaotic reflection related to complicated deformation in the frontier of a thrust belt. This detachment structure is notably incompatible with its neighboring areas in the regional structure and was formed in the Late Jurassic when the east-west napping led to a northwards descending terrain. The gravity drive is interpreted as the major cause of the northerly detachment along the coal layer in the proximity of the T_9 boundary. As a result, the Weizhou-Shigouyi detachment structure is bounded on the east and west by faults and occurs as a synclinorium comprising exotic sheeted rocks with simple deformation. Importantly, this study may help to understanding the tectonic evolution and planning the petroleum exploration.