Structures, deformation history and dynamic background of the Qianyingzi Coal Mine in the Huaibei Coalfield, eastern China

The Qianyingzi Coal Mine is located in the west of the Suxian Mining District of the Huaibei Coalfield, eastern China. The study on structural development patterns and genetic mechanisms in this mine lays an important foundation for safe and efficiently underground mining, and is also the key to understanding the regional tectonic evolution. In this study, based on the analysis of three-dimensional seismic, drilling and underground measured data and regional tectonic correlation, the structures, evolution history and dynamic background of the Qianyingzi Coal Mine are discussed. The Carboniferous-Permian coal measure strata in the mine are generally a gentle syncline with a NNE-trending axis, and cut by a series of faults. The faults developed in this mine are mainly medium- and small-sized with a throw of less than 20 m, and the number of reverse faults is significantly greater than that of normal faults. The strikes of reverse and normal faults are both mainly NE, followed by NNE and nearly N-S. According to the characteristics of structural geometry, tectonic association, fault property and cross-cutting relation, the structural deformation of coal measure strata in the Qianyingzi Coal Mine can be divided into five stages, and the corresponding tectonic stress fields are NWW-SEE compressive stress, nearly E-W compressive stress, NW-SE compressive stress, nearly E-W and NW-SE extensional stresses, respectively. It developed the Fengjia Syncline with a NNE-trending axis in the first stage and nearly N-S-striking reverse faults in the second stage, which were the results of foreland deformation and subsequent continent-continent collision during the convergence of the North China Craton and South China Plate in the Indosinian period. The NNE-striking reverse sinistral faults and NE-striking reverse faults developed in the third stage is 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 region. Later, the fourth and fifth stages of the nearly N-S- and NE-SW-striking normal faults were developed under the backarc extensional background in eastern China during the Early Cretaceous. These new results can be used to guide the rational arrangement for underground mining and also provide a new understanding for regional tectonic evolution of the Huaibei Coalfield.