Late Cretaceous Dongco granodiorite porphyry, Tibet: Product of lithospheric delamination

The Bangong-Nujiang suture zone is an important part of Tethyan tectonic domain, which is significant for revealing the evolution of Tethys Ocean, Tibet Plateau.The Late Cretaceous granodiorite porphyry in Dongco area from Southern Qiangtang terrane was selected to study petrology, zircon U-Pb age, Lu-Hf isotopic and whole-rock geochemistry.Zircon U-Pb dating and Lu-Hf isotopic analysis yields an age of 74.1±1.1 Ma, with positive ε_Hf(t) values of 4.5~6.9.Geochemical data reveal that the granodiorite porphyry belong to high-K calc-alkaline series, enriched in light rare earth elements with weak negative Eu anomaly and strong fractionation between light and heavy rare earth elements.In spider diagram, it is enriched in Rb, Th, U, K and Pb, and depleted in Ba, Nb, Ta, La, Ce, P and Ti.It is inferred that the granodiorite porphyry was derived from partial melting of thickened juvenile lower crust.Combined with previous research, it is concluded that the Dongco granodiorite porphyry was emplaced in post-collision tectonic setting as the product of lithosphere delamination, postdating the closure of Bangong-Nujiang Ocean.