Origin and tectonic implications of granitoids from the eastern segment of the South Altyn Block, North-western China: Constraints from petrogeochemistry, zircon U-Pb dating, and Lu-Hf isotope geochemistry

The South Altyn Block (SAB), located along the southern margin of the Altyn Tagh in Qaidam Basin, has a significant relationship with the tectonics of the Qaidam Basin basement. This study presents the petrological features, geochemical compositions, and zircon U-Pb and Hf isotope data of four granitic plutons from the eastern segment of the SAB to constrain the petrogenesis and tectonic setting of this region during the Palaeozoic. Basing on previous U-Pb dating results, the zircon U-Pb analysis in this study suggests that Palaeozoic magmatic events can be subdivided into four episodes: Late Cambrian (approximately 502 Ma), Late Ordovician (approximately 444 Ma), Early Devonian, and Middle Permian (approximately 271 Ma). The Palaeozoic granitoids were derived mainly from Neoproterozoic juvenile crustal components, with minor palaeoproterozoic ancient materials. The S- and I-type granitoids in Late Cambrian indicate a compressional tectonic environment with respect to subduction, and A-type granitoids suggest post-collision regime. The Late Ordovician granodiorites of A-type imply typical magmatism within a post-collision extensional setting. Ascribing to the subduction of Palaeo-Tethys Ocean during the Devonian, S-type granites were emplaced in the Early Devonian accompanied with the crust thickening. The Middle Permian magmatic events include a series of S-type granitoids, demonstrating the setting of oceanic subduction along with the closure of the Palaeo-Tethys Ocean.