The Tectonic Evolution And Its Effect On Mine Structure In Huaibei Coalfield

The tectonic system of Huaibei Coalfield is complex and affects the development of coal mining.Therefore,through the comprehensive and comparative analysis of the field typical structure observations,the structure of the geometry and kinematics characteristics,and combined with the stress-strain environment from the micro-deformation of tectonites,EBSD rock fabric features and vitrinite reflectance anisotropy in different mining area,this paper studies the formation and evolution of the tectonic system and its control mechanism on the development of mine structure from the coalfield.The following results are obtained:(1)The formation and evolution of Xuzhou-Suzhou arcuate Duplex-Imbricate fan thrust system have a key control effect on the construction of Huaibei Coalfield.The tectonic system in the section can be divided into the western leading edge belt,the central imbricate fan belt and the eastern hinterland belt with 3 sets of fold and faults structures from West to East,and they can make the area come into being a unique form of tectonic features called "North-South piecewise and East-West zoning",and have a profound effect on the tectonic development features of different mining areas(2)High angle normal faults are the main structure in Huaibei Coalfield,and reverse faults mainly developed in Xu-Su arcuate thrust and nappe structure of Sui-Xiao and Suxian mining area.The region of NE,NNE faults are more developed,but also developed NW reverse faults.The occurrence of the fault of the coalfield showed that the law is significant and each one has their own characteristic,and folds has an important impact on the structure of each mining area,coal distribution and preservation.(3)Analysis of microscopic deformation features of tectonic rocks shows that structures of microscopic deformation is mainly composed of the tension and shearing fractures,and the plastic deformation is weak.The configuration of the calcite group in the fault zone is mainly characterized by point maximum,small circle girdle or incomplete circle girdle.The main types of the fabric symetry are the monocline symmetry and triclinic symmetry.The calcite sliding system mainly consists of e twins slide and r translational slide,and the temperature range is lower than 200℃.The above analysis shows that Huaibei Coalfield that belongs to Xu-Su arcuate thrust and nappe structure is formed in the persistent low temperature and low pressure of shallow brittle deformation,low strain rate,with shear deformation properties,but there are some differences between different regions,and it has the superposition and complexity of motion.(4)Based on the finite strain analysis of vitrinite reflectance in the study area,it found that it is different obviously in the thrust and nappe of underlying system and overlying system.The minimum vitrinite reflectance of the overlying system mainly reflects the effect of SEE-NWW compressional stress field in Yanshanian,and the minimum vitrinite reflectance of underlying system mainly reflects the effect of the near NS compressional stress field in Indo-Chinese epoch.The above description shows that the deformation of Xu-Su arcuate thrust and nappe structure on the overlying system is stronger than the underlying system.(5)The development of mine structure is obviously controlled by the tectonic evolution of Huaibei Coalfield and formed a complex tectonic system in multi-stages tectonic evolution.Nearly NS directions’ compressive stress of Indo-Chinese epoch mainly form a stage of the near EW to the uplift associated with the reverse fault,but the impact on the study area is relatively small.The near EW extensional regime has a certain transformation effect on the early structure in late Yanshanian.Not only the formation of some near EW normal fault,but also it converse the pre-formed fault property under the action of the near NS extensional tectonic stress field.Mine structure has good response mechanism to the regional tectonic evolution and shows typical association feature of extension structure,thrust and nappe structure,strike slip structure and inversion structure in this area.The study area forms a specific structural system at different stages in the different evolutionary stages and mine areas dominated by horizontal tectonic stress.The prophase structure can be reformed and inherited or changed their properties in the later stage.