As the tectonic boundary belt, the south fault terrace, which consists of Wubao fault terrace and Zhenwu fault terrace, has complicated tectonic history and style.Based on the geometrical characteristics of the south fault terrace, guided by the stress-strain theory and extensional rate from the balanced section, we figured out the dominate extensional direction in different periods and analyzed the amount of extension and strike-slip of the south fault terrace, and their control on structural style.The evolution of the dominate extension direction of the Gaoyou sag can be divided into three stages since the late Cretaceous, including NW(K2t2-E2d), NS(E2s), and NW(Ny-Qd).Detailed understanding of the direction of stress field in the Gaoyou sag was obtained since the late Cretaceous in a quantitative way for the first time.Because the dominate extensional direction is not always parallel with the axis of fault terrace, Wubao fault terrace experie-nced 3 periods of tectonism, extension, right-lateral slip-extension, and extension.This resulted in the simple faults style with skew traces in plane view and horse tail-like in profiles.Similarly, Zhenwu fault terrace also experienced 3 periods of tectonism, left-lateral slip-extension, right-lateral slip-extension and left-lateral slip-extension, which resulted in the complicated faults style of grid fault trace in plane view and duplex horse tail-like in profiles.The study on the history of extension rate and strike-slip shows that E1f, E2d and E2s were the main periods of extension and strike-slip, which played a key role in the formation of structural style. © 2017, Editorial Office of Oil and Gas Geology. All right reserved.
