Formation of the orogenic curvature: Insights from the Triassic Xuefengshan Belt, South China

The Early Mesozoic Xuefengshan Belt, located in the central part of the South China Block, East Asia, developed as an intracontinental belt during the Middle Triassic. Analyses of structural and strain patterns in Neoproterozoic conglomerates constrain the internal deformation and three-dimensional kinematic evolution of this fold-and-thrust belt. Finite strain data (RXZ) range from 1.1 to 3.2 and generally increase eastwards towards the deep units that represent the orogenic core. Our results also show that at basal décollement zone the schistosity-forming deformation has a gradient of stronger fabrics, higher strain ratios, and a dominant thrust-normal flattening mechanism. High structural levels exhibit lower strain ratios and later structural overprinting that locally modified the early strain patterns. Parallel to the belt, enhanced strain and tectonic uplifting along the northern and southern sections of the belt indicate an along-strike structural variation that corresponds to the formation of the orogenic curvature. During the thrusting propagation, large igneous intrusions escaped deformation due to their stiffness and facilitated strain accumulation on the peripheries, whereas stress in the central section migrated progressively and formed a tectonic salient towards the west without significant strain localization.