MESO-CENOZOIC TECTONIC FEATURES OF THE WESTERN DEPRESSION OF THE EAST CHINA SEA SHELF BASIN

The Western Depression(WD), one of the important secondary tectonic units in the East China Sea Shelf Basin(ECSSB), is composed of many subordinate sags. It plays a key role in understanding the tectonic deformation in the ECSSB and adjacent areas since Late Cretaceous and in provision of references in the study of the Pacific subduction, conversion of continental margin type and other related scientific issues. Based on the seismic data interpretation and previous studies, we analyzed the structure framework of the WD in this paper. Both the Mesozoic and Cenozoic tectonic layers are well developed in the WD, and they are characterized by a series of Meso-Cenozoic extensional structural styles, such as half-grabens, titled faulted blocks, domino faults and so on, formed in late Cretaceous due to transformation of stress field from compression to extension. Meanwhile, along with the stress inversion at the end of Late Cretaceous, the positive inversion tectonic patterns also can be seen in the Changjiang Sag of the WD. The distribution patterns and features of faults in the WD vary with time, while the magmatic rocks change in distribution area, time, scale and lithology. Both faults and magnetic rocks are distributed upon the regional tectonic direction. Since Cretaceous, the drifting direction and the subduction angles of the Pacific Plate have become the main factors for the formation of the Mesozoic and Cenozoic tectonic structures in the WD. In addition, the collision, compression and subduction of the Philippine Sea Plate to the Eurasian Plate have made the tectonic pattern more complicated.