川西地区构造滑脱层岩石力学特征及构造变形意义

Lithomechanics of Décollement Layers and Tectonic Significance in the Longmenshan Thrust Belt, Western Sichuan

通过川西地区岩石样品单轴抗压强度测试和三轴抗压强度测试,认为岩石抗压强度与岩石密度具正相关关系。早期地层常具有较大的岩石抗压强度、弹性模量、泊松比,粘聚力亦具有类似变化趋势。构造滑脱层应具有相对较小的单轴抗压强度、较小的弹性模量和较小的泊松比。该区从上侏罗统至中奥陶统各地层中发育多套滑脱层,即上侏罗统蓬莱镇组、中三叠统雷口坡组、下泥盆统和志留系等。滑脱层在构造变形中多表现为各逆冲断裂下部汇聚或尖灭消失的构造软弱带,且滑脱层上部层位构造变形强度较大,多形成密集分布的逆冲断裂带,而滑脱层下伏区域构造变形微弱,多形成倾角较缓的单斜构造或者宽缓褶皱。

Many sets of décollement layers were developed in the western Sichuan basin,and these layers have an important influence on the process of tectonic deformation.This study does experiments of uniaxial compressive strength and triaxial compressive strength with rock samples from the studied area.The results show that there is a positive correlation between the compressive strength of rock and rock's density,and that the rock with older age usually has bigger compressive strength,with similar trends of elastic modulus,poisson ratio and cohesion.Therefore,the décollement layers should have smaller compressive strength,smaller elastic modulus and smaller poisson ratio.So several décollement layers were developed between the Upper Jurassic and the Middle Ordovician in the studied area such as:Upper Jurassic Penglaizhen Formation,Middle Triassic Leikoupo Formation,Lower Devonian and Silurian etc..These décollement layers are typical weak tectonic belts,leading lots of giant thrust faults merged or disappeared in them,and the sets of layer above the décollement almost have more intensive deformation than layer under sets,lots of thrust faults may be found in the above layers,however,only some gentle monoclines or wide folds were developed under the décollement layers.