有限元数值模拟技术在西湖凹陷中央反转构造带形成机制研究中的应用

在西湖凹陷中央反转构造带区域地质背景研究成果的基础上,基于有限元数值模拟技术,设计合理的有限元应力场模型和边界条件,模拟了西湖凹陷中央反转构造带的构造演化过程,探讨其成因模式。西湖凹陷中央反转构造带的构造演化过程可划分为3个阶段:(1)背斜带的初始形成阶段(始新世末,约32 Ma):在太平洋板块NWW-SEE向俯冲作用下,西湖凹陷的北部和中部地区分别形成了"A"背斜构造带和"B"背斜构造带两个不同高度的小背斜带;(2)背斜带的生长阶段(渐新世末,约23 Ma):在太平洋板块持续俯冲作用下,北部的"A"背斜构造带开始不断的向北扩展抬升,直至福江低凸起,背斜面积不断扩大。中部的"B"背斜构造带则不断的向南扩展抬升,当其扩展至西湖凹陷南部时,衍生出"C"背斜构造带和"D"背斜构造带两个小的背斜带;(3)背斜带的成型阶段(中新世末,约10 Ma):北部的"A"背斜构造带停止扩张,但垂向上仍继续抬升,抬升高度大于其它背斜构造带;中部和南部的"B"、"C"和"D"背斜构造带彼此连通,形成一个统一的大背斜构造带,由此东海陆架盆地西湖凹陷的中央反转带演化成型。

Application of the Finite Element Numerical Simulation Method to the Study on Formation Mechanism of the Central Inverted Structure Zone, Xihu Depression

On the basis of study on regional geological settings for the formation of the central inverted structure zone in Xihu Depression, the finite element numerical simulation method has been used for designing the reasonable finite element model to analyze the stress field and boundary conditions,and simulate the tectonic evolution history of the central inverted structure zone in Xihu Depression,and make cleat about its genetic model.The tectonic evolution of the central inverted structure zone in Xihu Depression can be divided into three stages.(1) The initial formation stage of anticline belt(late Eocene at about 35 Ma).During this stage,under the control of Pacific plate subduction in the direction of NWW-SEE,two anticline belts with different height formed in northern and central regions in Xihu Depression,namely "A" anticline belt and "B" anticline belt;(2) The growth stage of anticline belt(late Oligocene at about 25 Ma).During this stage,by the continuous subduction of Pacific plate,"A" anticline belt in northern part started to expand northward and uplifted continuously until to Fujiang lower uplift,and the area of "A" anticline belt has been enlarged continuously. While "B" anticline belt in central started to expand southward and uplifted continuously until to southern region of Xihu depression,then "C" anticline belt and "D" anticline belt developed;(3) The final formation stage of anticline belt(late Miocene at about 10 Ma).During this stage,"A" anticline belt in northern stopped expanding but uplifted continuously,and the uplift height was larger than other anticline belts.While,"B","C" and "D" anticline belt in central and southern parts connected to each other,and a single large anticline belt formed,thus the central inverted structure zone was finally shaped during this stage.