Early Paleogene strike-slip transition of the Tan-Lu Fault Zone across the southeast Bohai Bay Basin: Constraints from fault characteristics in its adjacent basins

The Tan-Lu Fault Zone (TLFZ) is the largest continental-scale strike-slip fault zone in East China. It experienced a complex Meso-Cenozoic deformation and controlled the development and evolution of the Bohai Bay Basin (BBB). Though its Mesozoic sinistral and Cenozoic dextral motions have been well documented, its strike-slip transition history and mechanism from sinistral to dextral motions in the Early Paleogene remain poorly understood. To investigate these issues, we made a thorough analysis on the fault geometry and kinematics as well as the response of depocentre in the Early Paleogene of the sags adjacent to the TLFZ across the southeast BBB. The results show that the WNW-/NW-, E-W-, and ENE-/NE-trending extensional faults developed in the Early Paleogene of those sags share almost the same geometrical and kinematic features. Such features indicate that the TLFZ is sinistral in Ek(3)-Ek(2) depositional stage, extension dominated in Ek(1) depositional stage, and dextral in Es-4(L) depositional stage. Such strike-slip transition of the TLFZ is a comprehensive effect of the plate events around the Eurasian Plate. The NNW-directed subduction of the Pacific to the Eurasian plates triggers the sinistral motion of the TLFZ during 65-55Ma, but this sinistral motion is terminated by the far-field effect of the NNE-directed India-Eurasia collision initiating at 55Ma. Then, the kinematic adjustment of the Pacific Plate from NNW to WNW breaks the stress balance exerted on the TLFZ by the subduction of the Pacific to Eurasian plates and the India-Eurasia collision and makes it turn into dextral motion gradually during 48-42Ma.