The structural deformation process and exploration of 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 features have recorded key information about 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 through detailed interpretation of multiple seismic profiles are analyzed, and based on this, the dynamic mechanisms of its structural evolution and deformation process are discussed. The results indicate that the Changjiang Sag has a "three-concave and two-convex" structure, with development of two major tectonic layers: 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 is a typical double-fault structure, with strata controlled by boundary faulting that exhibits a characteristic of being thicker to the east and thinner to the west. Since Cenozoic, influenced by multiple periods of 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 inversion tectonics have developed, with complex spatial stacking relationships, and the latter has the features of migrating from west to east. Since Miocene, stratigraphic deformation has been weak due to the buffering effect of the central uplift zone. Based on the characteristics of tectonic deformation, the tectonic evolution of the Changjiang Sag can be divided into five stages: Late Cretaceous-Early Paleocene extensional faulting, Late Paleocene-Early Eocene extrusion reversal, Eocene subsidence development, Oligocene tectonic uplift, and post-Middle Miocene overall depression stabilisation and deposition. This study can provide reference for basin structural deformation and regional tectonic evolution.