The Tectonic Evolution Of Yuquan Structure And Its Surrounding Areas In The East China Sea

This research based on a large amount of seismic and drilling data carries out calibration and structure interpretation to 10 seismic reflection horizon(Tg,T34,T32,T30,T21,T20,T16,T12,T10,T0) and exceed 30 two-dimensional lines surrounding Yuquan structure. It takes use of the thought of combining quality and quantity,regional and local structure research. Additionally the study apply various geological analysis methods such as section extension analysis,fault activity rate calculation,the reversal rate analysis of fault and balanced section study. In terms of geometry,kinematics and dynamics,the study simulation-analyze and research reverse tectonic style, reverse period, reverse strength and tectonic evolution process of the main target intervals systematically and quantitatively and it offers a reference to the oil and gas exploration of the basin。The study found that the Yuquan structure had mainly undergone three tectonic reverse movement such as Yuquan, Huagang and Longjing. The three movements partly correspond to three apparent regional unconformable surface such as T30(late Eocene),T20(late Oligocene),T12(late Miocene).Among them, the late Miocene Longjing movement(T12) is the strongest twisting-pressure reversion tectonic movement,enabling early developed central depressive basin uplift continuously and suffer erosion. Finally it create a modern central reversion structure framework. Because of the research of Yuquan structure geometry,we found that Xihu depressive basin was rich in reversion types and it could identify five basic reversion structure types in the research area:both the upper and lower normal model, lower normal and upper inverse model, both the upper and lower inverse model, lower concave and upper convex model, lower normal and upper uplift model. There are lots of inverse structure planar geometry combinations,such as y-shaped, anti-y-shaped, into-shaped,people-shaped, compound y-shaped. fire-shaped, flower-like-shaped and brush-shaped etc seven inverse tectonic combination styles.As to the inverse strengthen, the calculate result of the inverse tectonic activity rate and the inverse quantitative statistics to the research area showed that the central uplift reverse structure generally displayed a weaken trend from the north part (reverse fault activity rate and reverse the rate of respectively 5.3-5.9m/Ma,0.5-0.96) to the south (inversion tectonic activity rate and reversal rate were 2.3-2.8m/Ma.0.24-0.5).The penetration of northern reverse fault obviously stronger than that of the southern reverse fault.Through the production of the balanced section and the regional dynamics of the Yuquan structure, we can know that the Yuquan structure began to develop in the ancient-Eocene and it experienced multi-stage tectonic evolution. Prior to the Oligocene, the basin is characterized by extensional tectonic style. In the Oligocene-Miocene it dominated in extrusive tectonic style. From the Miocene to now it has generally developed regional extensive strike-slip structure. During the Cenozoic era, the basin generally evolve five stages such as the rifting-concave stage, the rupture-concave stage, the depression-concave stage, the reversal depression-concave stage and the regional subsidence stage. Different tectonic evolution stage has different tectonic effect. Every effect controls different tectonic styles and trap development and evolution of the basin.Yuquan structure developed a number of faults.It can be divided into one, two, three level fracture by the scope and impact. In addition,Through the drawing of the region structure. It can be found that the formation of reverse fault time is from north to south, from west to east.