Structural deformation and its dynamic mechanism of the Changjiang Sag in the East China Sea Shelf Basin

The Changjiang Sag is located in the northern part of the East China Sea Shelf Basin. Its tectonic development characteristics recorded and reflected key information on the formation and evolution of the basin and the process of plate convergence since the Late Cretaceous. However, the study on its tectonic deformation and dynamical mechanism is relatively weak. In this regard, the structural deformation characteristics and spatiotemporal differences of the Changjiang Sag were analyzed through detailed interpretation of multiple seismic profiles, and the dynamic mechanisms of its structural evolution and deformation process were discussed. Results indicate that the Changjiang Sag features a "three-concave and two-convex" structural framework with two major lithostratigraphic suits: Mesozoic and Cenozoic, primarily the Cenozoic, with the absence of the Oligocene. The overall depression is controlled by three sets of fault systems: NE, near EW, and NW, with local magmatic intrusion along the fault. The Changjiang Sag has a typical double-fault structure, and the strata were controlled by boundary faulting, being thicker in the eastern part and thinner in the western. Since the Cenozoic, Changjiang Sag has been influenced by multi-phased subduction and convergence of the Pacific Plate, the Indian Plate, and the Philippine Sea Plate, as well as the back-arc extensional processes. The tectonic system of the Changjiang Sag has undergone multiple transformations. Both extensional and inversional tectonics has developed, with complex spatial stacking relationships, and the latter features tectonic migration from west to east. Since the Miocene, stratigraphic deformation has been weak due to the buffering effect of the central uplift zone. Based on the characteristics of structural deformation, the tectonic evolution of the Changjiang Sag could be divided into five stages: extensional faulting in the Late Cretaceous-Early Paleocene, compressional and inversional activities in the Late Paleocene-Early Eocene, subsidence development in the Eocene, tectonic uplifting in the Oligocene, and overall depression, stabilization and deposition after the Middle Miocene. This study provided a reference for understanding the basin structural deformation and regional tectonic evolution in this area.