东海西湖凹陷沉降史与构造演化

The Burial History and Evolution of Xihu Depression

本文利用钻井及地震剖面资料获取现今地层厚度数据,通过去压实、构造剥蚀量及沉积物负荷校正,计算不同时期的沉降量及沉降速率,恢复凹陷构造沉降史;在此基础上应用McKenzie的均一多幕拉伸模型计算单井拉伸因子β,其结果表明西湖凹陷由北向南雁列式开裂成盆;综合构造沉降、拉伸因子计算结果,并结合构造应力场特征,本文将西湖凹陷的新生代构造演化划分为左行拉伸裂谷、热沉降和右行拉伸裂谷三大阶段。

The Xihu depression is located in the northeast of Eastern China Shelf basin. With the drilling and seismic reflection profile data, stratigraphic unit depth and its lithologic association are given to describe present sedimentary column, compaction coefficients and surface porosity of each strata sequence. It is calculated by geometric method used to calculate the depositional amount and subsiding rate of each depositing period, to review the sedimentary process and burial history by back-stripping modeling. According to MeKenzieg uniform lithosphere stretching modal, this paper analyzes the tectonic subsidence history and evolution of the Xihu depression by forward and reward modeling. The effect of eroding amount and sedimentary loading has been considered in the process of calculation. The sedimentary and tectonic subsiding rate history shows the character of three stage evolution： accelerate, decelerate and reaccelerate stages. Stretching factor β shows echelon distribution in plan map, and that the value of northern and southern sub-depressions decreases from north to south. The calculation result of tectonic subsidence history and stretching factor indicates that the echelon rifting of Xihu depression occurred from north to south. According to the character of stress field, the Cenozoic tectonic evolution of the Xihu depression could be divided into three stages： sinistral strike rifting （E1-E3 ）, following thermal subsidence （N1） and late dextral strike rifting （ N1 -Q）.