Formation and Forward Propagation of the Indosinian Foreland Fold-Thrust Belt and Nanpanjiang Foreland Basin in SW China

Orogenic growth, characterized by formation and forward propagation of fold-thrust belts and foreland basins, is predicted by wedge models of thrust systems. The growth of the Nanpanjiang fold-thrust belt and foreland basin system of the Indosinian orogenic belt in the southwestern South China remains poorly understood. The development of the Indosinian foreland system remains underappreciated due to few constraints on structural styles, kinematics and ages. Surface cross sections, seismic profiles and detrital zircon data are presented to address the structural styles and evolution of the Indosinian foreland system. The results reveal that the fold-thrust belt is characterized by fault-related folds with deeper duplexes and shallower imbricates, which yield a NNE-SSW regional shortening magnitude of similar to 36%. Our new constraints indicate that the Nanpanjiang region experienced multi-staged thrusting during the Indosinian orogeny (D-1). The D-1(1) affected the southernmost southern fold-thrust belt, producing thick-skinned thrusts involving Neoproterozoic basement and initiating the Nanpanjiang foreland basin. During the D-1(2), NNE-verging thick-skinned thrusting continued and was followed by thin-skinned thrusting in the northern fold-thrust belt. Locally preserved foreland basin deposits at the northernmost Nanpanjiang Basin define D-1(3). The progressive D-1(4) co-axially deformed the residual basin into a wide and gentle syncline. Thus, the progressive D-1(1) to D-1(4) deformation sequence of NNE-verging in-sequence thrusting and foreland basin migration describe the kinematic and dynamic relationship between fold-thrust belt and foreland basin during the Indosinian tectonic event. Indosinian D-1 structures were subsequently refolded by the Yanshanian tectonic event (D-2), forming N- to NE-striking cleavage and arcuation of D-1 fold axes.