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

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.