Petrogenesis and geodynamic significance of Neoproterozoic (∼925 Ma) high-Fe-Ti gabbros of the RenTso ophiolite, Lhasa Terrane, central Tibet

The Precambrian origin and evolution of the Lhasa Terrane remain unclear. Here, we present new zircon U-Pb isotopic and whole-rock geochemical data for the RenTso gabbros of the central Lhasa Terrane. These data indicate that these gabbros formed during the early Neoproterozoic (∼925 Ma) and have affinities with high-Fe-Ti basaltic rocks, given that they contain low concentrations of SiO2 (39.8-49.0 wt%) and high concentrations of FeOT (11.3-23.5 wt%), TiO2 (2.19-5.70 wt%), and V (333-1204 ppm). These gabbros also have N-MORB-like trace element features such as low (La/Sm)N ratios (0.50-0.57) and the absence of negative Nb-Ta anomalies. Combining these features with the high whole-rock εNd(t) (+5.04 to +7.55) and zircon εHf(t) (+7.8 to +13.0) values for these samples indicate that the RenTso gabbros formed by the partial melting of depleted asthenospheric mantle. The Fe-Ti enrichment in these gabbros reflects conditions of low oxygen fugacity during magma fractionation. These gabbros are spatially associated with troctolite and peridotite units, indicating that together these units form a typical ophiolitic lithological assemblage. These geochemical and field observations suggest that the study area contains a subduction-unrelated-type ophiolite that most likely represents the embryonic crust of the Mozambique Ocean following continental rifting and breakup. The results therefore indicate that the Lhasa Terrane has a Precambrian affinity with the East African orogen and occupied a different position to the Qiangtang Terrane within the Rodinia supercontinent.