Characteristics and geodynamic background of the coal-controlled structural patterns in the Qianyingzi Coalmine, Huaibei Coalfield

Abstract

The Qianyingzi Coalmine is located on the west of the Suxian Mining area of the Huaibei Coalfield, adjacent to the outer edge of the southern segment of the Xu-Su Arc Nappe Belt. Methods Based on the latest geological exploration and production data, this paper analysed the structural framework and coal-controlled structural patterns of the Qianyingzi Coalmine, divided the tectonic stages, and discussed the geotectonic background of the coalmine structures, Objective which provides an important geological basis for the understanding of the tectonic deformation and evolution of the coalmine, the geodynamic mechanism and the prediction of exploration directions. Results The results show that the Carboniferous-Permian coal-bearing formations in the mine are generally a gentle syncline with an NNE-trending axis. The faults in the mine are well developed, and the number of reverse faults is greater than that of normal faults. Both of these faults are mainly NE to NNE, followed by NS. The structural framework of this mine is significantly controlled by several large NS to NE-striking faults and is segmented from west to east by major faults, including the Nanping, F22, F17, DF200 and Shuangdui faults, which exhibit the characteristic of east and west zonation. The coal-controlled structural patterns in the mine can be classified into three types, namely, compressional, extensional and strike-slip. And the coal-controlled patterns can be further divided into nine subtypes, namely, thrust drag folds, hedge structures, pop-up structures, imbricate structures, grabens, horsts, step faults, positive flower structures and pinnated en-echelon structures. The analysis of structural combinations shows that the F17 fault has not only thrusting motion but also significant transcurrent activity. Conclusion The structural deformation of coal-bearing formation in the Qianyingzi Coalmine can be divided into five stages: the Fengjia Syncline with an NNE-trending axis, nearly NS-striking reverse faults, NNE-striking reverse-sinistral faults and NE-striking reverse faults, nearly NS-striking normal faults, and NW-SE-striking normal faults. Combined with the results of previous studies on the regional tectonic background, the first and second shortening structures in this mine are the results of foreland deformation during the convergence of the North China Craton and South China Plate and subsequent continent-continent collisional deformation during the Indosinian period. The third stage compresso-shear structures are related to the rapid oblique subduction of the Izanagi Plate toward the East Asian continental margin at the beginning of the Early Cretaceous in the Western Pacific. The fourth and fifth stage extensional structures developed against a strong extensional background in eastern China during the Early Cretaceous.

Keywords

• coal-controlled structural pattern
• tectonic stage division
• geotectonic background
• nanping fault
• qianyingzi coalmine
• huaibei coalfield