In situ zircon Hf-O isotopic constraints on the genesis of quartz diorite in Narusongduo Pb-Zn mining area, Tibet

Narusongduo Pb-Zn deposit is located in the southern margin of the middle Lhasa terrane. The characteristics of the magma source and genetic mechanism of the premetallogenic quartz diorite in the mining zone have not been well explained. The zircon oxygen isotope feature of quartz diorite in Narusongduo deposit is reported for the first time in this study. The age of quartz diorite is 83.0 Ma, which is consistent with the late Cretaceous 'magma burst' in the south Lhasa terrane. The zircon Hf-O isotope composition is relatively uniform, Hf (t)= -2.55~0.99, with the average value of -0.80, the corresponding tDM2 is 1088~1312Ma; and the 18O values range between 6.50 and 7.87, with the average value of 7.15. In situ zircon Hf-O isotopic measurements for the samples yield a binary mixing trend between mantle and continental crust, with mantle-related components as a primary contributor. Combined with other geochemical characteristics, the late Cretaceous magmatism in Narusonduo deposit is part of the late Cretaceous 'magma burst' in the south Lhasa terrane. It is the response to the late Cretaceous magmatism caused by the northward subduction of the Neotethyan. Our study shows that the significant late Cretaceous magmatic activities are not only limited in the south Lhasa terrane, but also blossomed in the middle Lhasa terrane.