Differential magmatism and tectonic evolution during the rift stage within the Baiyun Sag of the Pearl River Mouth Basin in the northern South China Sea

To investigate the magma-related formation mechanisms and structural evolution of sags within a passive continental margin setting/configuration, we selected the Baiyun Sag in the Pearl River Mouth Basin (PRMB) and identified its spatiotemporal magmatic distribution during the rift stage based on high-precision 3D seismic data, drilling data, and geochemical data. Totally three stages of syn-rift magmatism were revealed. Strong and continuous crustal extension and thinning, crustal extension and thinning with simultaneous magmatic activity, and intermittent crustal extension and thinning were suggested to be the development mechanisms of the main Baiyun Sub-Sag (M-BSS), eastern Baiyun Sub-Sag (E-BSS), and western Baiyun Sub-Sag (W-BSS), respectively. Complex multi-stage magmatism is the direct cause of the formation of high-angle sag-controlled faults with lowangle detachment characteristics in the Baiyun Sag. In addition, we explored the genesis of the multi-episodic magmatism, dynamic mechanisms, and differential evolution of fault basin structures in the Baiyun sag, which are essentially related to the reactivation of Mesozoic pre-existing faults, the differential extensioninduced flow of the Cenozoic lithosphere material, and the along-fault magmatic material upwelling. This study not only serves as a significant guidance for oil and gas exploration in the Eocene strata of the northern SCS, but also provides insightful ideas for analyzing magmatic and tectonic activity in other petroliferous basins with a similar setting.