3D Structure of the Mesozoic Tan-Lu Fault Zone and Its Impact on Basin Evolution: Insights from the Southern Bohai Bay Basin, NE China

The Cenozoic Tan-Lu Fault Zone, as the largest strike-slip fault system in eastern China, features complex deformation patterns and mechanisms and a tectonic evolution process that has been investigated by previous studies. Here, we present high-resolution seismic profiles across the whole southern Bohai Bay basin, linked to the Tan-Lu Fault Zone that allow us to observe two types of Mesozoic fault systems: an E-W trending basement fault set, and a NNE trending basement fault set. Considering the tectonic events that have happened since the Mesozoic and the intersection relationship between the two fault systems, we propose that the E-W trending basement faults are thrust faults, which can be attributed to the Triassic collision between the South China Block and the North China craton. The NNE trending basement faults are interpreted as strike-slip faults formed during transpression, due to multiple phases of subduction of the Pacific plate during Jurassic to Late Cretaceous. Both fault systems have been reactivated as normal faults during Early Cretaceous rifting, leading to the formation of a conjugate rift basin. The widespread Early Cretaceous extension promoted volcanic activity, allowing significant volumes of deep-seated magmatic material to rise along these two sets of faults and to erupt onto the surface. The spatial distribution of the volcanic products was structurally controlled by fault boundaries, leading to the formation of a large-scale, quadrangular Mesozoic volcanic basin.