陆内山前冲断结构分带的构造物理模拟实验

Physical modeling of thrusting structure zonation in front of an intracontinental orogen

冲断带物理模拟实验的现有模型无法模拟完整变形带,不完全符合中国复合陆内冲断的构造背景。通过设计具有横向、垂向流变差异的“挤压—碰撞”模型,模拟了冲断结构的分带特征和过渡带内逆断层演化。几何学分析表明,改进的实验模型可以模拟完整的变形带,从腹陆向前陆依次为厚皮带、过渡带、薄皮带,分别对应造山带、冲断带和盆地;断层的发育规律方面,实验模型与地质模型亦具有较好对应关系。运动学分析表明,过渡带内逆断层的演化经历了脆性变形、韧—脆性变形和韧性变形3个阶段,但有无滑脱层会造成逆断层的演化有所差异。横向上断层发育规律分析表明,初始破裂角小和演化时间短是冲断带内前缘逆断层倾角小于后缘的成因机制。

Existing experimental models do not simulate complete deformation zones,and do not totally match with the background of the composite intracontinental thrust belt in China.This work simulated the zonal charac teristics in thrust structures and the reverse fault evolution in the transitional zone by building a“compressioncollision”model which has rheological heterogeneity in vertical and horizontal directions.The geometric analysis shows that the improved model can simulate the complete deformation zones.The order is thick skinned zone,transitional zone and thin skinned zone from hinterland to foreland,which correspond to the orogen,thrust belt and basin,respectively.Moreover,fault development in the experimental model corresponds well with the geolo gical model.The Kinematic analysis shows that the development of reverse faults in the transitional zone has gone through three stages:brittle deformation,ductile-brittle deformation and ductile deformation,but the evolution of thrust faults varies with the presence or absence of a detachment layer.Besides,the small initial fracture angle and short evolution time are the controls for the formation of thrust belts in which the dip angle of the front thrust fault is less than that of the back one.