Discovery and geological significance of the andesite intercalation in the"Dibuco Formation"of Nixiong area,central Tibet
Due to the lack of high-precision chronological constraints,the age and stratigraphic attribution of the"Dibucuo Formation"in Nixiong area are controversial.In this paper,the weighted average age of 120 Ma was obtained through zircon U-Pb dating from the andesite intercalation in the"Dibucuo Formation".These data,in combination with the existing research data on detrital zircons of the"Dibucuo Formation"in the studied area,led us to conclude that the so-called"Dibucuo Formation"was formed in Early Cretaceous(130～120 Ma),which is consistent with the formation age of the volcanic-sedimentary strata of the Zenong Group in this region.It is thus suggested to tentatively classify the"Dibucuo Formation"into the Zenong Group.According to the whole-rock geochemistry of andesite samples and the in-situ zircon Hf isotopic composition,it is believed that the andesite was derived from the mixture of crust-derived felsic magma and mantle-derived basaltic magma,and formed in the subduction tectonic environment.By further summarizing and analyzing the spatio-temporal transformation of Meso-Cenozoic magmatism in the Lhasa terrane,it is revealed that the dynamic mechanism of the formation of this set of andesites is mainly related to the northward subduction of the Neo-Tethys oceanic slab.
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