How was intraplate deformation in the Youjiang tectonic belt of southwestern South China influenced by marginal orogenesis?

The dynamics of Mesozoic intraplate deformation within the South China block and its association with plate-margin orogenesis have long been debated. To address this issue, we conducted detailed structural mapping and zircon U-Pb dating in the Youjiang tectonic belt of the South China block. The results indicate four phases of deformation (D1−D4) that produced three standard types and 10 subtypes of superimposed folds. D1 is characterized by top-to-the-W thrusting at 244−237 Ma. D2 is divided into D21, D22, and D23. D21 comprises top-to-the-NE thrusting at 237−218 Ma, D22 generated top-to-the-SW back-thrusting ca. 218 Ma, and D23 is characterized by top-to-the-NE thrusting at 218−187 Ma. D22 overprinted D1 with an angle of ∼60° between f1 fold axes and the maximum principal compressive stress P22, resulting in type 1d, 1e, and 1f superimposed folds. D23 overprinted D1 with an angle of ∼30° between f1 and P23, resulting in type 2a superimposed folds. The different types of superimposed folds can be distinguished by the angle between the early fold axes (fe) and the orientation of the subsequent maximum principal compressive stress (Pl). D3 is characterized by top-to-the-NW thrusting at 175−127 Ma. D3 overprinted D1 and D2 folds, forming type 1a, 1b, and 1c or type 2a and 2b superimposed folds, depending on the geometry of the earlier folds. D4 is characterized by NE-trending normal faults that formed at 93−82 Ma. Changes in kinematics and the types of superimposed folds were related to clockwise rotations of the South China block by ∼30° and ∼5°−10° during the Triassic and Jurassic−Early Cretaceous, respectively. Intraplate deformation in the Youjiang tectonic belt was generated by progressive propagation of the foreland fold-and-thrust belt during Triassic collision of the South China block and Indochina, and selective reactivation of the Jiangshan-Shaoxing suture zone along the existing weak tectonic belt during Jurassic−Cretaceous subduction of the Paleo-Pacific plate. The superimposed folds of the Youjiang tectonic belt were formed as a result of clockwise rotation of the South China block from the Triassic to Cretaceous.