Geometry and kinematics of Wensubei-Yeyungou fault and its implication for the genetic mechanism of North Tarim uplift

Abstract：The structural deformation of paleo-uplifts in the cratonic basin is an ideal place to explore the deformation behaviors in the interior of the tectonic plates and the continental ductile structural geology, with the study of faulting being a breakthrough point in this aspect. Based on the newly acquired geophysical data and the recently finished exploratory wells, this paper discusses the fault systems of the north Tarim uplift of the Tarim basin, especially the geometry and kinematics of the northern boundary fault of Tarim basin. It is discovered that the Wensubei-Yeyungou fault acts exactly as the northern boundary fault, having distinct reflections in the gravitational and magnetic fields as well as along the seismic profiles. It is 600 km in length, and is composed of three segments from west to east, i.e., Wensubei fault, Wenbashi fault, and Yeyungou fault. It was first produced at the end of Early Ordovician, resulting from the breakthougth at the front limb of a large fault-related fold system caused by the subduction of the thrust fault into the basement ductile detachment zone from the south to the north. It took its shape at the end of the Caledonian movement. By the end of Permian period, responding to the strong compression from the north, the southward thrust tectonic system not only took the shape of the former detachment zone, but was also superimposed upon and modified the former Caledonian thrust tectonic system, giving rise to a large-scale anti-form thrust system consisting of a series of small-scale fault blocks, and made the whole fault zone take its shape finally. During the Himalayan movement, the tensile-torsional fault system was developed along the axial zone of the north Tarim uplift. The Wensubei-Yeyungou fault zone was subjected to sinistral transpression, and the re-activation was propagated from the east to the west. Hence it was characterized by prolonged evolution, multi-stage development, inheritance, superposition, and compounding. It had a marked trend of a strong-weak-strong evolution process, namely, the activity was strongest in the early Paleozoic, became weakened or calm in the Mesozoic-early Cenezoic period, and got stronger once again in the late Cenezoic. The faulting in the western segment was possibly much stronger than that in the eastern segment. Its formation was largely related to the collision between the Tarim continental block and the peripheral terrains due to the closing of the North Kunlun Ocean at the end of the early Ordovician, the closing of the South Tienshan Ocean at the end of Permian, and the closing of the Neo-Tethyan Ocean in the Paleogene respectively. These phenomena suggest the important influences of the adjacent plate tectonic events upon the intra-plate deformation. The fault zone seems to be an important oil and gas accumulation zone. The study of the mechanism and evolution is helpful to the expansion of hydrocarbon exploration in the area, as evidenced by the discovery of oil and gas resources in the Xiqiu anticlines.