Cenozoic evolution and deformation in the Eastern and Western Depression of the Liaohe Subbasin, Bohai Bay Basin: Insights from seismic data

In rift basins with multiphase extension, the reactivation of pre-existing faults plays an important role in the evolution and partitioning of deformation. The Liaohe Subbasin is located in the northeastern Bohai Bay Basin, and the Tanlu Fault Zone (TLFZ) runs through it and experienced extension and right-lateral strike-slip during the Cenozoic. Therefore, it is an ideal region for studying the deformation and evolution of rift basins. Based on 3D seismic data, we document the structure and fault characteristics of the Eastern and Western Depressions of the Liaohe Subbasin, identify periods of activity on normal and strike-slip faults, and analyse the evolution and mechanisms of the Cenozoic evolution of this subbasin. Our main results show that (1) the main faults in the Western Depression exhibited extensional motion throughout the Palaeocene, while the Eastern Depression exhibited significant right-lateral motion during the Oligocene following the early extension stage. (2) The Cenozoic evolution of the Liaohe Subbasin can be divided into four stages: (i) an initial extension stage (the Palaeocene to the Eocene), (ii) an extension stage with initial strike-slip (Early Oligocene), (iii) a right-lateral strike-slip stage (Late Oligocene) and (iv) a postrift stage (after the Neogene). (3) The upwelling of mantle material caused by the subduction and rollback of the Pacific Plate led to the extension of the Liaohe Subbasin from the Palaeocene to the Eocene. The TLFZ began right-lateral motion at 40 Ma and experienced strong right-lateral deformation when rifting was weak in the Oligocene and enhanced deformation after 12 Ma. (4) In this multiphase rifting process, under moderate obliquity, strike-slip deformation is obvious in the areas close to pre-existing faults, while extensional deformation is obvious in areas farther away. (5) Cenozoic extension and strike-slip deformation due to partitioning of strain are caused by obliquely reactivation of TLFZ. This study suggests that the reactivation of pre-existing strike-slip faults plays a major role in evolution and strain partitioning. Moreover, the results will contribute to future hydrocarbon exploration in multiphase rift basins.