鄂尔多斯盆地西缘煤田构造演化及其控制因素

鄂尔多斯盆地西缘位于华北陆块和秦祁昆山造山带两个一级大地构造单元之间的过渡带内, 特定的大地构造背景使其具有复杂的构造演化历程及特殊的煤田构造格局。鄂尔多斯盆地西缘由贺兰山逆冲推覆构造系统和六盘山东麓逆冲推覆构造系统组成, 具有"南北分段、东西分带"的特点。为了进一步探讨鄂尔多斯盆地西缘煤田构造格局的形成演化及区域构造控制因素, 本文基于野外地质调查和煤田勘查资料, 恢复了本区自晚古生代以来的沉降抬升史和古构造应力场特征。印支期: 研究区北部最大主压应力方向为北西—南东向, 南部最大主压应力方向为北东—南西向, 燕山期: 北部最大主压应力方向为北西西—南东东向, 南部最大主压应力方向为北东东—南西西向, 喜马拉雅山期: 北部受北西西—南东东向拉张应力, 南部最大主压应力方向为北东—南西向。采用有限元数值模拟, 探讨了鄂尔多斯盆地西缘煤田构造格局的形成与区域构造的演化的关系, 强调北段贺兰山逆冲推覆构造系统的形成与阿拉善地块的向东挤出逃逸密切相关。

Coalfield tectonic evolution and its controlling factors at the western margin of Ordos Basin

The western margin of Ordos Basin is located within a transitional zone which is between two first-order tectonic units of distinct properties, namely the North China block and the Qinglin-Qilian-Kunlun orogen. Due to the unique tectonic setting, the study area experienced complicated tectonic evolution and formed special structure framework of coalfields. The western margin of the Ordos Basin is composed of two structural systems, respectively named the Helanshan thrust-nape system and the eastern Liupanshan thrust-nappe system, and is characterized by north-south trending segmentation and east-west trending zoning. For the further study of coalfield tectonic evolution and its controlling factors at the western margin of Ordos Basin, this paper, based on field geological investigation and coalfield exploration, carried out the reconstruction of the subsidence and uplift history and the analysis of paleo-tectonic stress fields since Late Paleozoic. During the Indo-Chinese epoch, the maximum principal compression stress shown NW-SE trending in the north area, and show NE-SW trending in the south area. During the Yanshanian epoch, the maximum principal compression stress show NWW-SEE trending in the north area, and show NEE-SWW trending in the south area. During the Himalayan epoch, the maximum principal compression stress show NE-SW trending in the south area, but there is NWW-SEE trending tension state in the north area. The relation between regional tectonic evolution and formation of structural framework in coalfields at the western margin of Ordos Basin was discussed by finite element numerical simulation. In addition, the close relation between the formation of Helanshan thrust-nape structural system and eastward extrusion of Alax block is highlighted.