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

Foreland fold–thrust belts act as key engines of continental growth and reworking by accommodating crustal shortening and internal deformation during long-term continental evolution. Within these systems, the formation and propagation of thrust wedges represent the primary mechanisms by which shortening is accommodated and translated into the horizontal growth of orogenic belts. However, current understanding of thrust wedge evolution in foreland systems remains largely based on static structural interpretations, providing limited quantitative and time-resolved constraints on kinematics, strain partitioning, and wedge propagation mechanisms.

Here we investigate thrust wedge formation and propagation in a multilayered continental crust using analogue sandbox experiments inspired by the Western Xuefeng fold–thrust belt of South China, a representative intracontinental orogenic system. Two sets of experiments were designed to simulate different detachment configurations and lateral variations in rheology. Anisotropy of magnetic susceptibility (AMS) and particle image velocimetry were integrated to quantitatively constrain strain distribution, kinematic evolution, as well as velocity and vorticity fields within thrust wedges.

By reproducing multilayered deformation in foreland fold–thrust belts, the sandbox experiments provide a quantitative framework to link thrust wedge propagation with the redistribution of strain and the horizontal growth of orogenic belts. The experiments reveal that the cover sequence deforms as three distinct tectonic levels, each characterized by specific thrust wedge geometries: stacked thrusts forming an active roof duplex at the bottom level, box-shaped anticlines at the middle level, and imbricate systems with chevron-shaped folds at the upper level. In Model 2, a lithological transition from shale to siltstone across the Lower Cambrian Qiyueshan Fault led to mechanical coupling between the middle and bottom levels in the west, producing thrust wedges with chevron anticlines above a single shallow detachment. In contrast, the southeast region, controlled by three detachments and surface erosion, developed box-shaped anticlines. These observations indicate that abrupt lateral changes in lithology strongly influence thrust wedge styles and transitions. Furthermore, AMS measurements capture the magnitude and orientation of strain within the wedges, highlighting how lithofacies variations modulate deformation mechanisms and strain partitioning.

Based on quantitative analyses of wedge kinematics and strain, we propose a new thrust wedge dominated multilayered propagation model in the Western Xuefeng fold–thrust belt. This framework connects local wedge dynamics to continental-scale crustal evolution, providing a basis for understanding fold–thrust dynamics in intracontinental orogens worldwide.