Ocean–continent transition of the northeastern Paleotethys during the Triassic: Constraints from Triassic sedimentary successions across the Qinling Orogen, central China

Abstract

To decode the northeastern Paleotethys ocean–continent transition process, a geological profile is constructed across the southern Ordos Basin, central Qinling Orogen, and northern Sichuan Basin. Along the transect, abundant detrital zircon age data, sandstone petrological compositions, and paleocurrent directions taken from the Triassic sedimentary successions across the Qinling Orogen reveal systematic tectonic variations in ocean–continent transition processes. The Early Triassic sedimentary succession was deposited in a foreland basin which was part of the northeastern Paleotethys Ocean and received recycled North Qinling Orogen detritus in a collisional tectonic setting. This evidence implies that the North Qinling region was undergoing intense erosion during the subduction of the Paleotethys oceanic crust. In the Middle Triassic, continued subduction brought the foreland basin in the Huicheng region to an end, and the depocenter migrated westward to the West Qinling and Songpan-Ganzi regions under a convergent collisional tectonic setting. In the Late Triassic, the West Qinling and Songpan-Ganzi regions were still receiving sediment, while the North and South China Blocks entered the continental collision process. The detrital material in the southern Ordos Upper Triassic Yanchang Formation continued to be eroded from the North China Block in a collisional tectonic setting. The sediments in the northern Sichuan Basin were mainly sourced from the South China Block and South Qinling area in a collisional setting, and the Songpan-Ganzi region continued to converge and eventually evolved into a collisional tectonic setting. The Paleotethys ocean–continent transition represents a complete second half of the Wilson cycle, and mountain building preconditioned the paleotopography and influenced the basin formation.