Mesozoic and Cenozoic tectono-thermal reconstruction of the western Bohai Bay Basin (East China) with implications for hydrocarbon generation and migration

Studies on the tectono-thermal evolution of the western Bohai Bay Basin (WBBB), including the Jizhong Sub-basin and Cangxian Uplift, are important for further petroleum exploration and exploitation. This study aims to reconstruct the tectono-thermal history of the WBBB based on a combination of 125 vitrinite reflectance (Ro) data and seven apatite fission track (AFT) and nine apatite (U-Th)/He (AHe) ages. The effective AFT ages range from 60.3 to 97.0 Ma, with mean track lengths of 10.86–12.64 μm. The variable single-grain AFT ages are explained to be due to the parameter D_par. The effective AHe ages range from 21.1 Ma to 75.0 Ma. Two rapid cooling events revealed by the thermal modeling results occurred during the Early-Late Cretaceous (130–90 Ma) and Late Eocene-Early Miocene (40–18 Ma), respectively. The Fuping Complex, which is located in the western margin of the WBBB and mainly composed of the Paleo-proterozoic high-grade gneisses, experienced the intensive extension-detachment during the Early-Late Cretaceous along with the subduction of the Izanagi Plate, that was probably responsible for the first cooling event. The second cooling event was caused by the subduction of the Pacific Plate during the Middle Eocene-Early Miocene (43–23 Ma), as well as the collision of the Indian and Eurasian Plates and the rollback of the subducting Pacific Plate during the Early Miocene (23–18 Ma). The WBBB experienced two heat flow peaks of ∼75 and ∼80 mW/m² during the Early Cretaceous and the Late Eocene, respectively. During the Late Eocene-Early Miocene, rapid subsidence in the Baxian Depression (one secondary tectonic unit of the Jizhong Sub-basin) coupled with the rapid uplift in the Cangxian Uplift caused the Shahejie Formation of the middle-upper Eocene to generate gas during the Early Miocene. Meanwhile, tectonic movement during the Early Miocene also caused faults to become migration paths, as revealed by the homogenization temperature of the fluid inclusion. This study provides new insights regarding the tectonic and hydrocarbon evolution of the WBBB.