Magnetic fabrics of the South Dabashan Belt at the north margin of South China: Constraint on the origin of the arcuate trace of Chengkou Fault

Abstract

The South Dabashan Belt at the northern margin of the South China Block is a typical arcuate-shaped orogenic belt in western China. Its formation and evolution are important for understanding the collisional orogeny and intracontinental deformation in the South Qinling Orogen and its foreland basin. Anisotropy of magnetic susceptibility (AMS) can provide fabric patterns which can be used to discuss the strain of the South Dabashan Belt. Rock magnetism reveals that paramagnetic minerals dominate magnetic susceptibility and some ferromagnetic minerals also exist. Magnetic fabrics of Triassic and Jurassic strata are essentially type II fabric with well-developed magnetic lineation; further, they rarely show sedimentary fabric, indicating the early stage of the deformation processes. Magnetic fabrics show that early horizontal shortening strain is characterised by a radial pattern in the South Dabashan Belt. Our results indicate that the Chengkou Fault initially formed as a normal fault with arcuate shape during the opening of the Mianlue Ocean and has a controlling effect on the formation of the curved fold-and-thrust belt. Then, the later shortening strain overprints the previous deformation but barely changes the curvature of the Chengkou Fault.