岩石强度对冲断层形成特征影响的砂箱实验研究

Experimental study with sandbox of the influence of rock’s intensity on formation of thrusts

实验通过地形变化的砂箱模型模拟了两盘岩石强度差异对冲断层形成特征的影响作用。模型设计为在基底收缩参与的情况下 ,变形前地面坡度递增的单侧挤压系列。实验结果显示 ,当变形前地形水平乃至初始地面坡度很小 (<7°)时 ,挤压作用形成两组倾向相反的冲断层。若初始地面坡度显著 (>7°) ,则只形成倾向与挤压方向相反的一组冲断层。结合应力分析认为 ,若两盘岩石强度均一或相近 ,挤压作用形成两组对冲断层 ;当强度明显差异的两盘发生碰撞时 ,强度大的一盘优先向能量弱的方向释放能量 ,形成向另一盘仰冲的一组冲断层。实验结果与陆陆碰撞带剖面断层形态上有较好的相似性。

This experiment simulates the influence that the difference of rock’s intensity of two blocks exerts on the character of thrusts. The models are compressed from one direction with contractive substrate and the initial surface of models is oblique with gradually increasing gradient. The results show that if the original surface is level or the initial gradient is smaller than 7 degrees, the compression induces two groups of thrusts with opposite dip. If the original surface gradient is greater than 7 degrees, the compression causes one group of thrusts whose dip is opposite to the compressional direction. Stress analysis shows that the compression induces two groups of thrusts whose dip are opposite if the two walls have consistent or similar intensity. As two walls whose intensities are obviously different are pressed together, the stronger wall will release energy towards the weaker one first, as a result a series of thrusts with one wall abducting upon another can be formed. The result of experiment is very similar to the actual section of collision zone between two continents.