基于粒子成像测速(PIV)技术的褶皱冲断带砂箱构造物理模拟研究

Sandbox Modeling of Fold and Thrust Belt Based on Particle Image Velocimetry(PIV)

在前人对褶皱冲断带的研究基础上,为进一步深入分析对比滑脱层数量、强度、深度等对褶皱冲断带的制约,设计了6组砂箱模拟实验,并运用粒子成像测速(PIV,Particle Image Velocimetry)技术的实时监测,计算出各阶段模型剖面上的速度场和涡度场,对褶皱冲断带的运动学过程和变形机制进行详细刻画和定量分析。实验结果表明,滑脱层的强度和深度均制约着褶皱断层的构造演化,滑脱层的强度越小,其上覆地层中的变形传播越远,滑脱层深度越深,对整个构造样式更具有控制作用,变形也就传播得更远。以微玻璃珠组成的滑脱层主要产生前展型逆冲叠瓦式构造,上部推覆体前缘水平位移较快;以硅胶组成的滑脱层上部形成叠瓦式构造,下部形成冲起构造,上、下两部分具有明显的分层变形特征。PIV监测结果显示,当上盘速度骤停,并且前缘涡度值骤降时,断坡形成并发展成断坪-断坡组合构造样式;下一条断层以相同方式在前缘形成,从而使褶皱冲断带向前陆方向扩展。将实验结果与龙门山南段褶皱冲断带进行了对比分析,得到了较好的印证。

Based on previous studies, this study used sandbox modeling to analyze the constraint of the number, intensity and depth of slip layers to the fold-thrust belt. Using particle image velocimetry （PIV） as a real-time monitoring technology, six sandbox modeling experiments were designed to calculate the velocity and vorticity of models to quantitative analyze kinematic and deformational mechanism of the fold-thrust belt. The results show that （ 1 ） the strength and depth of slip layers constrain the tectonic evolution of fold faults ; （2） the smaller the strength of slip layers is, the farther the deformation propagation of overlying strata is ; （3） the slipping depth is deeper, and the control action on entire structure is larger, thus the deformation spreads farther. The slip layer which is composed of micro-glass beads mainly produces preshow type of thrust imbricate structure, with faster rate of upper horizontal displacement at the nappe front edge. The upper layer which consists of silica gel main- ly generates imbricated structure, with washed form from the lower part of the formation. The upper and lower portions of the slip layer show distinct characteristics of hierarchical deformation. The PIV analysis shows that the ramp off the floor forms and develops into a combination of structural-style ramps when the disk speed arrests and the vorticity of the leading edge rapidly decreases, and the following fault forms in the same manner at the front edge, leading to the forward expansion of the fold-thrust belt. The comparative analysis of the southern section of the Longmenshan fold-thrust belt and experimental results shows good consistency.