三峡工程库首区及狮子口重力滑动构造系统的构造应力场研究

STRESS FIELD OF THE EASTERN AREA OF THE YANGTZE GORGE RESERVOIR AND THE SHIZIKOU GRAVITATIONAL GLIDING SYSTEM

基于野外实测和室内测试、计算分析及有限元模拟，对三峡工程库首区燕山期和喜山期的区域构造应力场以及狮子口重力滑动构造应力场进行研究。区域构造应力场的主要特征是：燕山主期σ＿１和σ＿３近水平，分别近Ｓ—Ｎ向和Ｅ—Ｗ向，σ＿２近直立，差异应力２００ＭＰａ、变化范围１５０～２５０ＭＰａ；喜山主期σ＿１近水平，总体方向ＮＥ７０°—ＳＷ２５０°，差异应力１００ＭＰａ，变化范围８０～１２０ＭＰａ。在空间变化上，前者表现为南部差异应力高于北部差异应力，后者的变化规律不太明显。狮子口重力滑动构造系统的应力场比较复杂，总体呈近Ｅ—Ｗ向的前缘挤压、后缘拉伸，而滑动系统内部叠置产出的三个滑块也分别表现出后缘拉伸、前缘挤压并交替出现的特点，反映了区域应力场背景下的局部构造应力场特征。

Systematic study on the regional stress field in the eastern area of the Yangtze Gorge Reservoir and the local stress for the Shizikou gravitational gliding system has been carried out by stereographic and statistical analyses on numerous conjugate joints, slickensides, styolites and microstructures including fractures with their veinlets, pressure solution seams and tectonic lenses. The regional principal compressive stress (σ1 ) is determined to be horizontal with two stress groups directed S-N and NEE 75°-SWW250° respectively. Based upon quantitative analysis on regional paleostress field by rock rupture criterion combined with e-twin ratio and dislocation density methods, the differential stress during S-N compressive deformation is estimated at 200MPa. whereas that during NEE 75°-SWW250° compression at 80-120MPa. The cross-cutting relationships between conjugate joints, fault striae, microstructures and regional faults and folds indicate that the S-N-and NEE 75°-SWW250°-oriented compressions were active during the main stages of the Yanshanian and the Himalayan movements respectively. It is shown by finite-element simulation that the Yanshanian differential stress in the southern area has higher strength than that in the northern section. In contrast, no significant spacial variations in differential stress have been found for the Himalayan compression. Stereographic and statistical analyses on minor structures inside the Shizikou gravitational gliding system reveal that the stress field of that system is generally characterized by front-edge compression and back--edge extension with gently dipping σ3 towards NE-SW and moderately dipping to nearly vertical of at the back edge, and gently dipping of towards NE-SW and moderately dipping to nearly vertical a3 at the front edge. The stress field of the Shizikou gravitational gliding system is defined to be the local one superimposed on the regional field yielded by the main stage of the Yanshanian movement.