Salt-layer coupling controls active deformation and foreland landscape: Insights from the Kuqa fold-and-thrust belt, Northwest China

Coupling among deep-crustal structures fundamentally controls crustal rheology and deformation across multiple scales. Weak and mobile salt, acting as a highly ductile quasi-fluid, plays a key role in mediating this coupling from shallow to deep-crustal levels. However, how spatial variations in salt-layer coupling shape surface deformation and landscape evolution remains poorly understood. The Kuqa foreland, Northwest China, with spatially variable salt bodies, provides a natural laboratory for addressing this question. We integrated morphotectonic mapping, Quaternary geochronology, seismic-profile interpretations, and quantitative geomorphic analyses to examine how salt-layer thickness and coupling among basement, salt, and sedimentary cover control active shortening and surface morphology. Results show that in western Kuqa, thick salt layers (>3 km) promote partial to full structural decoupling, accommodating 3−4 mm/yr of active shortening in the hinterland Kelasu belt and ∼2 mm/yr across the frontal Qiulitage belt. Long-term uplift of both belts produced a symmetric subsidence center and a longitudinal river-dominated landscape. In eastern Kuqa, active shortening deformation is concentrated in the frontal Qiulitage and Yaken anticlines, where basinward thrust propagation and distal decoupling above the region’s thick salt layers (>3 km) generate asymmetric subsidence and transverse river-dominated landscape. Low-relief, high-channel-steepness landscapes reflect buried, active detachment folding along gypsum-salt layers. These findings highlight the fundamental role of salt-layer coupling in linking deep geodynamic processes to surface deformation and foreland landscape evolution.