Detrital zircon characteristics of Paleoproterozoic-Ordovician in the Olongbuluke Terrane: implication for the affinity of Olongbuluke Terrane and the closure of the Proto-Tethys Ocean

The Qilian-Qaidam Orogenic Belt (QQOB) belongs to the western Central China Orogenic Belt (CCOB), recording a nearly complete evolutionary history of the South Qilian and North Qaidam Ocean (branches of the Proto-Tethyan Ocean). However, some debates still exist, such as the affinity and amalgamation processes of microblocks in the western CCOB and the closure time of the South Qilian and North Qaidam Oceans. The Olongbuluke Terrane (OLT), as a connecting area located at the central of QQOB, where Precambrian to Paleozoic sedimentary successions are well developed, offers a unique window to address the tectonic history of the South Qilian and North Qaidam Ocean basins. In this study, detrital zircon UPb ages combined with ophiolitic, magmatic and high-pressure to ultrahigh-pressure metamorphic records and field investigations, indicate that the OLT was part of a passive continental margin during the early Paleozoic and there was still a microblock, named the North Qaidam Terrane (NQT), between the Qaidam Block (QB) and the OLT. Considering the regional geology, at ca. 517 Ma, an obvious provenance change occurs in the OLT, inferring the collision between the OLT and NQT. Subsequently, the North Qaidam Oceanic plate subducted to the NQT, and the North Qaidam Ocean closed at ca. 450 Ma. The similar detrital zircon UPb age spectra of simultaneous deposit flysch sequences between the Shihuigou Formation in the OLT and the Balonggonggaer Formation in the South Qilian Accretionary Belt indicates the onset of collision between the OLT and CQT at ca. 458 Ma. The detrital zircon UPb age spectra of microblocks from the early Paleozoic strata of the northern Tibetan Plateau shared a North Indian affinity, indicating that the closure of the Proto-Tethyan Ocean may relate to the formation of the Gondwana landmass. Until the late Devonian to early Carboniferous period, with the opening of the Paleo-Tethyan Ocean, the QB, OLT and CQT drifted as an entirety from the Gondwana landmass.