Subduction to closure of the Bangong–Nujiang Meso-Tethyan Ocean: Constraints from Mesozoic magmatic rocks in the Jiang Co area, north-central Tibetan Plateau

Abstract The subduction and closure of the Bangong–Nujiang Meso-Tethyan Ocean remain unresolved, hindering our understanding of the early evolution of the Tibetan Plateau. Here we present new data for Jurassic–Cretaceous andesitic and granitic rocks from the Jiang Co area of the north-central Tibetan Plateau. Jurassic magmatic rocks have zircon U-Pb ages of ca. 160 Ma and variable εHf(t) values of −10.2 to +0.5. They show geochemical affinities with high-Mg diorites and I-type granites. High-Mg diorites typically formed from melts of sediments that interacted with the overlying mantle wedge. Concurrently, I-type granites commonly originated from the mixing of magmas derived from the crust (Amdo–Dongka Co terrane) and mantle. These rocks suggest that the southern branch of the Bangong–Nujiang Meso-Tethyan Ocean probably experienced initial intraoceanic subduction in the Middle–Late Jurassic. Cretaceous granitic rocks have zircon U-Pb ages of ca. 110 Ma and negative to positive εHf (t) values of −6.4 to +5.2. Compared with Jurassic magmatic rocks, these rocks are more compositionally diverse, involving calc-alkalic metaluminous–peraluminous ferroan (A2-type) and highly fractionated I-type granites that were generally derived from magma mixing between ancient crust and depleted mantle. These rocks usually formed in a collisional setting, which indicates that the Bangong–Nujiang Meso-Tethyan Ocean had closed by this time. Finally, we propose that the Bangong–Nujiang Meso-Tethyan Ocean experienced four-stages of tectonic evolution during the Middle Jurassic to Early Cretaceous: initial intraoceanic subduction (170–155 Ma), flat subduction (155–140 Ma), slab rollback (140–130 Ma), and continental collision (120–110 Ma) during the Mesozoic. The timing of the final oceanic closure is regionally constrained to 130–120 Ma.