Magmatism and mineralization in the Sangye-Qulong magmatic section, Southern Tibet

Abstract

The Sangye-Qulong magmatic section in the Gangdese belt of southern Tibet records magmatic evolution spanning from oceanic subduction to continental collision. This work combines zircon U-Pb geochronology, whole-rock geochemistry, and Sr-Nd isotopes from pre-, syn-, and post-collisional intrusions along a ∼ 60 km NE-SW section. Results reveal that the Cretaceous high-Mg diorites originated through partial melting of oceanic slab, while the low-Mg adakitic granitoids (91.6 ± 1.5 Ma) were formed via lower crust melting. Syn-collisional Paleocene-Eocene granitoids (64.1–52.5 Ma) originated from juvenile lower crust during slab rollback. Miocene adakitic granitoids were derived from the thickened lower crust, and dioritic enclaves (16.5 ± 0.2 Ma) show a mixing trend between lower crust adakitic melts and Indian continental crust.

The Cretaceous rocks are hydrous and oxidized, associated with the Kelu Cu-Au mineralization. The scarcity of mineralization in syn-collisional rocks is largely linked to their limited water content and low oxygen fugacity. The Miocene rocks related to the Qulong porphyry deposit have the highest Sr/Y, V/Sc, Eu/Eu*/Y ratios and most enriched Sr-Nd isotopes, indicating high magmatic water content, oxygen fugacity, and the greater involvement of the Indian continental material. These findings demonstrate the Indian continental slab’s crucial role in the formation of post-collisional porphyry deposits.