New insights on the geometry and kinematics of the Shunbei 5 strike-slip fault in the central Tarim Basin,China

摘要

Integrated geological-geophysical methods have been used to depict the geometric characteristics and kinematic evolution of the Shunbei 5 (SB5) and adjacent Shunbei1 (SB1) strike-slip faults in the central Tarim Basin, China. Geometric evidence for strike-slip faulting includes the occurrence of positive and negative flower structures in stepover zones, oblique secondary splay faults, en echelon folds, and adjacent secondary faults. The multihumped along-strike and along-dip displacement variations of the SB5 fault provide insights into the initial segmentation, interaction and polycyclic growth of the fault zones both in plan and section views: The SB5 fault initiated as an apparent "X-type" conjugate pure shear fault system in the north and a simple shear fault system in the south respectively. At depth (mainly in Cambrian to Middle Ordovician rocks), the northern and southern parts of the SB5 fault exhibit a typical dextral strike-slip architecture consisting of multiple fault segments connected via transpressional push-up or transtensional pull-apart stepovers or bends. The southern part has a linear, narrow sinistral ridge system. At shallower depths (in Upper Ordovician to Middle Devonian rocks), the lower subvertical faults propagated upwards as en echelon normal faults in the north, and as a two-phase, partitioned system consisting of boundary grabens and en echelon normal faults that dissected the earlyformed border grabens in the south. With progressive deformation, the northern and southern parts of the SB5 fault reactivated and transferred into one large, sinistral fault in Upper Devonian to Permian rocks. Four major tectonic phases matching the kinematic evolutions of regional fault systems and uplifts in the study region, have also been recognized in the Middle Ordovician to Cretaceous. The pull-apart stepover and single fault zones developed in Middle Ordovician rocks are favorable fracture-related reservoirs.