Discovery and geological significance of concealed thrust-fault at medium and big depth in the south of Hancheng mining area

To guide geological exploration, the Paper analyzed the deformation characteristics of concealed thrust fault, revealed the formation mechanism of the fault, carred out the structural prediction. Through the fine surface observation, 2D seismic exploration and verification of drilling engineering, on the basis of discovery and understanding of the morphological features of structures, the coupling relationship between shallow structures and deep structures was analyzed. In combination with the stress field of paleostrcture, the genesis of structures was elaborated. The results showed that the north-south and deep concealed thrust faults were dipping to the west and thrusting to the east, the dip of the fault plan is 20°~35°. The faulting took place inside Shihezi Formation, underlying coal-bearing measures and their basement. The vertical throw is 190~260 m, the horizontal displacement is 260~470 m. The shallow strata occurred as unidirectional assymmetrical anticlines. The shallow strata and the deep strata were closely associated in space, interrelated in geometry and kinematics, unified in genesis. The shallow anticline was the result of fault-propagation folding under control of deep overthrusting. The concealed thrust-fault was the response to the reverse thrust faulting induced by the tectonic crushing stress in the basin during middle Yanshan orogeny. The thrust fault dislocated coal seams, led to repetition of seams, controlled the spatial distribu-tion of coal seams, constituted important tectonic boundary in the mid and deep part of the south of Hancheng mining area.