Abstract:

 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 mainly 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.

Key words: sandbox modeling, slip layer, velocity field, vorticity field, fold-thrust belt, the southern section of Longmenshan