Intra-continental Dabashan orocline, southwestern Qinling, Central China

Using field investigation, structural analysis, and 40Ar–39Ar and fission-track geochronology, we synthesize the structural architecture, stress fields, and tectonic evolution of the Dabashan orocline, southwestern Qinling. Three paleostress fields govern deformation: The first (Late Triassic to Early Jurassic, T3–J1) reflects ∼N–S to NNE–SSW shortening in the foreland of the Qinling–Dabie orogen and is the result of the collision of the North China and Yangtze blocks; the principal structures in the Dabashan belt are ∼E-trending folds. The second event (Late Jurassic to Early Cretaceous, J3–K1) shows NE–SW shortening; a fold-thrust belt formed with ∼150 km shortening above a detachment layer at 10–12 km depth. During this event, the Dabashan foreland acquired its convex-to-southwest oroclinal shape. The third event (Late Cretaceous to Paleogene, K2–E) reflects ENE–WSW or NE–SW extension coeval with the formation of local basins. The Dabashan orocline formed due to pinning of the Qinling–Dabie thrust front at two basement culminations within the subducting Yangtze craton; foreland progradation was made possible by the activation of a Lower–Middle Triassic gypsum-salt detachment of the Sichuan-basin sedimentary pile. During expansion, movements were radially along the orocline. This study gives an example of intra-continental orogeny when terminal deformation is governed by foreland heterogeneities.

► This work gave a case study that an intra-continent orogen formed finally in J3–K1. ► The orocline was controlled successively by three stages of paleo-stress fields. ► The orocline largely experienced three episodes of deformation since Mesozoic.