Late Cretaceous Gabbros in the Yanhu Area, Northern Xizang: Implications for the Post-collisional Delamination Process of the Bangong-Nujiang Suture Zone

Late Cretaceous magmatic rocks are extensively exposed along the flanks of the Bangong-Nujiang Suture Zone in central Qinghai-Tibet Plateau. However, the geodynamic mechanism has always been controversial due to the lack of constraints on the mafic rocks. Here, we report zircon U-Pb age, whole-rcok major and trace element geochemistry, and zircon in situ Hf isotopes of gabbros in the Yanhu area, Northern Xizang, to provide new constraints on the geological evolution of the Bangong-Nujiang Suture Zone. Zircon U-Pb dating results indicate that gabbros formed at 100 Ma with εHf(t) values of 6.60–8.33. The results show that the gabbros have geochemical affinity to OIB-type rocks but have obvious depletion of Nb-Ta. These geochemical features indicate that the gabbros belong to intraplate mafic rocks, derived from the partial melting of the upwelling asthenosphere with various degrees of crustal contamination. Our results, combined with those of the regional coeval mafic dykes and high-Mg adakitic rocks, demonstrate that the gabbros were formed in post-collisional extension setting, which was triggered by the delamination of the over thickened eclogitic lower crust after the Lhasa-Qiangtang continental collision. The identification of the Yanhu gabbros provides direct petrological evidence of mantle convection induced by post-collisional delamination in Northern Xizang. © 2024 Science Press. All rights reserved.