Control of strike-slip and pull-apart processes to tectonic transition of the southern East China Sea Shelf Basin

The East China Sea Shelf Basin (ECSSB) lies among the Eurasian Plate, the Pacific Plate, and the Indian Plate. Its formation and evolution since the Mesozoic was controlled by the combined effect of westward subduction of the Pacific Plate and actions of the large-scale ductile shear zone on the South China Platethe Changle-Nan'ao Fault Zone. This paper selects the southern ECSSB with well-developed Mesozoic strata as the study area. By analysing the basin architectures and structures of each structural unit, calculating the fault growth index, and referring to the sandbox modelling results, we consider that the Oujiang Sag belongs to a strike-slip pull-apart basin controlled by the Changle-Nan'ao Fault Zone, while the Minjiang Sag and the Jilong Sag are extensional basins without strike-slip property. The Mesozoic evolutionary process of the ECSSB can be divided into three stages on the basis of the three main strike-slip movements of the fault zone. In the Middle-Late Jurassic, the subduction of the Izanagi Plate induced the dextral shearing in a ENE direction of the Changle-Nan'ao Fault Zone, which then formed NW-SE-directed transpressional structures inside the ECSSB. In the Late Jurassic-Early Cretaceous, the motion sense of the Izanagi Plate gradually shifted to the northwestwards, inducing the sinistral-thrusting of the fault zone. Following this, the initial NW-SE-directed compressional structures were stretched into the original sag. By the Late Cretaceous, the retreat of the subducting Paleo-Pacific Plate led to the turning of the regional stress field from compression to transtension. Being influenced by the dextral strike-slip-related structures of the Changle-Nan'ao Fault Zone, the Oujiang Sag developed extensive strike slipping-related structures and was assembled into a left-stepping en echelon pattern. The Minjiang and Jilong sags, however, gradually grew into extensional depressions under successive extension due to the great distance from the strike-slip fault zone.