Abstract: The maximum length of overthrusts has long remained an unresolved enigma in structural geology. Theoretical
calculations typically limit their lengths to approximately 16 kilometers, yet geological observations, particularly in foreland basins, often reveal overthrusts extending far beyond this limit, reaching hundreds of kilometers. For instance, overthrust in the Southwestern Tarim Basin spans 230 kilometers, significantly exceeding theoretical predictions. This study employs analogue modeling based on the geological prototype derived from structural interpretation of the Hetian-Mazhatage seismic reflection profile. Four experimental setups are designed to investigate the formation mechanisms of ultra-long-distance overthrusts by simulating syn-tectonic growth strata (via adjustments to brittle cover thickness) and modulating the shear yield strength of the ductile décollements (through variations in silicone viscosity). Experimental results demonstrate that the low-viscosity décollements significantly enhance the forward propagation of deformation in the foreland direction, increasing both the velocity and distance of strain transfer. Conversely, high-viscosity décollements impede such propagation. Additionally, the inclusion of syn-tectonic growth strata in the models amplifies decoupling effects, accelerating and extending strain transfer toward the foreland, thereby facilitating the development of long-distance overthrusts. The experiments reveal that the synergistic interaction between low-viscosity décollements and syn-tectonic growth strata constitutes a critical precondition for the formation of ultra-longdistance overthrusts in the Southwestern Tarim Basin. These findings provide novel insights into the mechanisms governing the development of ultra-long-distance overthrusts in natural settings.

Key words: Southwest Tarim Foreland Basin, analogue modeling, overthrust, décollements, syn-tectonic growth strata