Coalfield tectonic evolution and its controlling factors at the western margin of Ordos Basin
Cao Daiyong1, Xu Hao1, Liu Kang1, Wei Yingchun1, Zhan Wenfeng2, Wang Xinguo3
1. College of Geosciences & Surveying Engineering, China University of Mining and Technology, Beijing 100083;
2. Beijing Polytechnic College, Beijing 100000;
3. Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085
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.