Middle to Late Triassic felsic and mafic magmatism in the eastern West Qinling Orogen, Central China: A record of the Paleo-Tethyan oceanic crust advance to retreat

Abstract

The tectonic setting of Indosinian magmatism in West Qinling Orogen and the tectonic evolution of the Paleo-Tethys remain hotly debated. Here we present SHRIMP zircon UPb dating, major-trace elemental and Sr-Nd-Pb-Hf isotopic data for four granitic and gabbroic plutons across the eastern West Qinling Orogen, from north to south including Guanshan, Fengxian, Mishuling and Miba. Our new data indicate that the Fengxian granitoids, emplaced at 238 Ma in a continental arc setting, show adakitic affinity and were formed by partial melting of subducted sediments. The southern Guanshan granitoids, emplaced at 235–229 Ma in a continental arc setting, also show adakitic affinity but were generated by partial melting of thickened (>50 km) lower crust. The northern Guanshan granites and gabbros were emplaced at 217–216 Ma in a back-arc setting, with the former generated by partial melting of normal (40–50 km) lower crust and the latter derived from asthenospheric mantle. The Mishuling granitic pluton contains abundant mafic microgranular enclaves, both emplaced at 214 Ma in a back-arc setting with the host granitoids formed by partial melting of normal (40–50 km) lower crust and the enclave magmas derived from asthenospheric-lithospheric mantle. The Miba granitoids, emplaced at 216 Ma in a continental arc setting, show adakitic affinity and were generated by partial melting of thickened (>50 km) lower crust. We suggest that the Paleo-Tethyan oceanic crust had subducted near the Shangdan suture by 238 Ma and successively advanced northward, approaching southeastern Qilian Orogen at 235–229 Ma. Then slab rollback initiated and gradually migrated southward. The slab subduction did not cease before 214 Ma.