Provenance of the Devonian Liuling Group sandstones: Constraints on Paleozoic North–South China Block tectonics

Abstract

The Devonian Liuling Group (DLLG) and its surrounding strata provide massive information about the Paleozoic subduction–suture–extension process of the North China Block (NCB) and South China Block (SCB). Systematic field-based sedimentology, sandstone modal composition, whole-rock elemental composition, and detrital zircon U–Pb dating were employed. The sedimentary sequence of DLLG shows that the water depth deepened and then shallowed, which is characteristic of an extensional basin. Analysis of the tectonic setting and geochronology revealed that the fore-arc sedimentary system (FAS) and DLLG were sourced from the North Qinling Belt (NQB) and NCB. An age population with a single peak at 420 Ma from the FAS suggests that the island arc existed at 420 Ma, indicating that the subduction of the Shangdan Ocean did not finish until the late Silurian. The DLLG deposits were mainly from basement material of the NQB, indicating that the Shangdan Ocean closed before the Middle Devonian, which implies that the NQB and South Qinling Belt (SQB) were spliced during the Early Devonian. This rapid transition from subduction to extension and the absence of molasse hint that no full orogeny occurred during the suture process and that the DLLG formed in a post-suture extensional rift basin.