南沙海槽南缘逆掩推复构造地区的动力学分析

Dynamic analysis of nappe structure region in the southern margin of the Nansha Trough

提出南沙海槽南缘推复构造的运动和形变是一种周期性的弹塑性运动 ,周期约为 1 4Ma .建立推复楔形体的动力学模型及两个约束条件 ,求解得推复楔形体的底部中点的推复方向的主应力和逆掩面动摩擦系数的解析式 .建立推复楔形体前缘地层被推复剪断的力学模型、密度模型和内摩擦角模型 ,求得推复前缘地层被推复剪断时的有效主应力、静岩压应力、推复方向的主应力及其合力和推复构造应力的解析式 ,建立推复底部的有效塑性屈服模型 ,求得推复底部屈服时中点的有效主应力和推复方向的主应力的解析式 .选择两个剖面进行动力学计算 ,得到推复楔形体前缘的两个应力图、逆掩面的动摩擦系数及推复方向的主应力的合力 .

The movement and deformation of nappe structure in the southern margin of the Nansha Trough are proposed, which have elasto plastic periodicity,and the periodicity is about 1 4 Ma.Based on the dynamic model and two restricting conditions established for accretionary wedge of the nappe,the analytic solutions of principal stress in thrust direction at the midpoint of the nappe base and dynamic friction coefficient of thrust fault planes are presented.By establishing mechanical model of shear fault formation,density model and model of angle of internal friction which are in the front strata of the accretionary wedge of the nappe, effective yielding principal stress,lithostatic pressure,principal stress in the thrust direction and their resultant force,structure stress are solved for forming shear fault during overthrust.By establishing effective plastic yielding model in the nappe base,principal stresses of being effectively yielded and the thrust direction at the midpoint of the nappe base are solved.Two sections are selected to make dynamic calculation,and two stress figures, the dynamic friction coefficients of thrust fault planes and the resultant force of the principal stress in the thrust direction are obtained.