不同变形速率下前陆褶皱冲断带的发育特征——基于砂箱物理模拟实验研究

Correlationship between Deformation and Various Shortening Velocities of Fold-and-Thrust Belt: Evidence from Sandbox Modeling

构造模拟实验是研究和模拟自然界地质构造现象、变形特征、成因机制和动力学过程的一种物理实验方法。本文基于砂箱构造物理模型高、中、低速7组不同单向挤压速度的构造模拟实验,揭示不同变形速率下砂箱物质变形的几何学、运动学及其演化特征,探讨不同变形速度（尤其是不同量级速度）对前陆褶皱冲断构造变形的重要性。高速单向挤压变形过程中（0.4-0.1mm/s）,砂箱模型中石英砂体后缘构造加积强烈,砂体变形主要以楔形体向前扩展变形为主,其构造样式主要表现为前展式叠瓦冲断构造。中速挤压变形过程中（0.05-0.005mm/s）,砂体后缘加积相对较弱,构造变形样式主要为砂箱楔形体前缘先形成（前展式为主）逆冲断层,当达到临界楔形体后,反冲断层发育并与前展式逆冲断层构成冲起构造,构造样式上表现为叠瓦构造与冲起构造的无序叠加。低速挤压变形过程中（0.002mm/s）,砂箱物质构造样式以典型冲起带为主。由于砂箱模拟过程的时效性,即如何在最有效时间内获得最全面而复杂的演变过程,通过本次系列实验,我们建议将此有效挤压速度设定为0.05-0.005mm/s范围内,可以先后清晰而全面的获得高速和低速挤压下砂体的变形过程和构造样式。

Brittle deformation in shallow crust is generally characterized by a long tectonic history and complex geological features which result from interdependent parameters. Using similar initial conditions of sandbox model（ pure quartz sand thickness： 15 mm,10 mm,10 mm and red quartz sand thickness： 1 mm）,we investigated different geometry kinematics and evolution of a thrust wedge with various shortening velocities.Under high velocity（ 0. 4 - 0. 1mm / s）,the thrust wedge shows strong shortening and deformation along the wedge back,which is characterized by piggyback imbricate-thrust structures. Under lower velocity（ 0. 05 - 0.005 mm / s）,the thrust wedge is characterized by gentle deformation and piggyback imbricate thrusting at first,followed by out-of-sequence retro-thrusting and backward pop-up structure after a critical wedge has been achieved.In particularly,Under the lowest velocity（ 0. 002 mm / s）,the deformation is characterized by Pop-up structure.Due to the temporality of sandbox modeling under low shortening velocities（ i. e.,how to unravel the maximum likelihood,the most complex deformation process with a most effective time）,the choice of an effective shortening velocity is vital for the mechanism sandbox model. Therefore,we suggest a suitable and low velocity range（ 0. 05 -0. 005 mm / s） can set down in most of our modeling.