Study On The Controlling Factors Of Fold-Thrust Belt

The fold-and-thrust belts is a transitional zone between the orogenic belt and the basin,formed by regional extrusion stress with fold and reverse thrust deformation as the main tectonic deformation zone.This zone records the process of orogenic belt deformation and propagation to the foreland,and a full understanding of the factors controlling the occurrence and development of folding and retrograde faulting is important in understanding the development of fold-and-thrust belts and orogenic belts.The deformation of fold-and-thrust belts is related to various factors such as the rate of shortening,crustal thickness,décollement,syn-rift deposition,and climate.Analogue modeling is the main tool used to understand the mechanism and dynamics of tectonic deformation.Previous studies have analyzed the factors influencing the fold-and-thrust belts,but most have focused on univariate experiments,while the mechanism of the combined influence of multiple factors on tectonic deformation has not been systematically studied.To clarify the influence of brittle slip layer,ductile slip layer,pre-existing faults,and syn-rift deposition on the development of fold-and-thrust belts,we designed six sets of targeted physical analog modeling.The six sets of experiments are bilaterally symmetric extrusion experiments that compare the number of brittle slip layers,slip layers in pre-existing fault-bearing environments,and slip layers in syn-tectonic deposition and pre-existing fault-bearing environments,respectively.We combined the velocity field,strain field,and fault formation time obtained from PIV analysis to reveal the influence of the combination of slip layers,syn-rift deposition,and pre-existing faults on the development of foldand-thrust belts.The experimental results show that in the purely brittle strata,a single brittle slip layer accelerates the lateral transfer of tectonic deformation and facilitates the further formation of foreland faults.The double-layer uniform brittle slip layer slows down the propagation of tectonic deformation and stores the stress to inhibit the formation of foreland punching faults.In the environment with pre-existing faults,the pre-existing faults are preferentially propagated around to form conjugate folds.In the environment where the pre-existing faults are present,the slip sheets have the effect of separating the tectonic storage stresses vertically and accelerating the stress transfer to the preexisting faults horizontally.In a syn-rift depositional environment with pre-existing faults,the slip layer has the effect of draping and decoupling the brittle layers separated by sedimentary amplification,and the slickensides enhance the amplification of tectonic deformation in the depositional environment.The experimental findings validate previous geological interpretations of the folded belt in the east Sichuan area and provide a theoretical basis for the role of the double slip layers in controlling the development mechanism of the folded belt.