Material Composition of Diaoyu Islands Folded Zone and Reanalysis of Eastern Boundary of Prototype Basin of Xihu Sag in East China Sea

The restoration of Paleogene prototype basin is a key problem related to the study of sedimentary system and hydrocarbon accumulation of Huagang Formation and Pinghu Formation in the main exploration strata in Xihu Sag, whereas a reasonable understanding of the structural evolution of Diaoyu Islands folded zone in the east margin of Xihu Sag is the key to the problem.However, relevant studies are often limited by the weak data base of the research area.In this paper a breakthrough in the geological understanding through the comprehensive analysis of gravity, magnetic and seismic data innovatively is obtained.It is believed that in the early stage the Diaoyu Islands folded zone was part of the "East China Sea shelf outer margin uplift" and underwent intense magmatic hyperplasia in the later stage.Structurally, the part under the T20 interface in the folded zone is mainly composed of ancient metamorphic basement, magmatic rock mass and residual sag filling layer.The residual sag and strata in the folded zone are characterized by NE-trending and enechel on distribution.These strata are mainly Eocene Pinghu Formation deposited before Oligocene magmatic hyperplasia and transformation, and are the residual part of the eastern margin of the Paleogene prototype basin of Xihu Sag.The eastern boundary of the Paleogene prototype basin of Xihu Sag is located in the current Diaoyu Islands folded zone, and is a series of NE-trending faults in enechel on distribution, and there are different types of transition between faults.In the process of magmatic proliferation in the Diaoyu Islands folded zone, the rock mass upwelling along the boundary fault "submerged" the boundary of the prototype basin.The strata in the eastern margin of the prototype basin underwent large-scale uplift and denudation, and the original structural appearance and morphology were greatly changed.