Thrust Wedge Dominated Multilayered Propagation Using Finite Strain Sandbox Modeling: Growth of the Western Xuefeng Fold‐Thrust Belt, South China Block

AbstractFormation and propagation of thrust wedges in foreland fold–thrust belts are critical for the horizontal growth of orogenic belts. Based on the multilayered detachment system of the Western Xuefeng fold–thrust belt (WXFT), two sets of sandbox models were established to explore the thrust wedges propagation mechanisms. Anisotropy of magnetic susceptibility (AMS) and particle image velocimetry were used to quantify velocity, vorticity, and strain evolution of thrust wedges. Both models reveal that the cover sequence deforms as three distinct tectonic levels, each characterized by thrust wedges composed of flat–ramp thrusts and hanging wall folds. The bottom level features stacked thrusts forming an active roof duplex; the middle level develops box–shaped anticlines; and the upper level forms imbricate systems with chevron–shaped anticlines. Model 2 simulates a lithological transformation from shale to siltstone in the Lower Cambrian westward across the Qiyueshan Fault. This led to mechanical coupling of the middle and bottom levels west of the fault, where a single shallow detachment produced thrust wedges with chevron anticlines. In contrast, the southeast developed thrust wedges controlled by three detachments and erosion, forming box–shaped anticlines. Thus, thrust wedge styles and transitions may be significantly controlled by the abrupt change in mechanical properties of the Lower Cambrian in the WXFT. Additionally, the AMS results captured the strain state and intensity within the thrust wedges, further illustrating the influence of lithofacies variations on deformation mechanisms. We proposed a new thrust wedge dominated multilayered propagation model in the WXFT, with implications for understanding fold–thrust systems globally.