Structural characteristics and time constraint of Late Mesozoic intracontinental deformation in Xishan meiyao area, south of Beishan

The Xishanmeiyao area of southeastern Beishan range, presents an opportunity for investigating the intracontinental deformation history of Central Asia region during the late Mesozoic era, which is of great significance to revealing the evolutionary history of Central Asian. Here, we conducted synthesis investigation of remote sensing image interpretation, field geological observation and structural analysis, and apatite (U−Th)/He (A−He) chronology to study the deformation characteristics and time in the Xishanmeiyao area. The study area exposes the Xishanmeiyao thrusts, which is characterized by the thrusted the late Carboniferous gabbro and Permian granite to the Middle Lower Jurassic Longfengshan Formation coal-bearing strata (J_1-2ln). A series of the NE direction imbricated thrust faults were developed with fault dip is 40°~50° in the footwall. The gabbro and granite klippen forming on the hang wall with the thrust nappe distance of ~10 km. The AHe data of the late Carboniferous gabbro record the 160~130 Ma cooling event, it is indicated that the area experienced near NE compression deformation during the late Middle Jurassic to early stage of Early Cretaceous, which may be the coupling result of the closure of Bangong−Nujiang ocean final in the southern and the Mongolia−Okhotsk Ocean in the northern margin of Asia. The AHe data of deformed Jurassic record the 120~100 Ma cooling event related the footwall exhumation during subsequent normal faulting, which may be the caused by the collapse of thickened crust. The tectonic inversion of the near E−W normal fault causing that the deformed Jurassic and overlying rocks were overlayed to the Lower Cretaceous, indicative of the weak compressive deformation after Late Cretaceous in the southern part of Beishan and overprinted the pre-existing compressive and extensional structures.