Chronology And Geochemistry Of Magmatic Rocks Of The Xuru Tso Batholith In Central Lhasa Terrane, Tibet

There are many Mesozoic magmatic rocks in the Lhasa Terrane, Tibet that has recorded many important informations of plateau tectonic evolution and deep process. The Lhasa Terrane has received considerable attentions by scholars as a natural laboratory of the continental-continental collision research. This years, many study of magma source regions and petrogenesis of the Cretaceous magmatites has been well conducted, while the study of the Late Jurassic granitoids in the central Lhasa Terrane, Tibet is still limited. In this paper, we focus on the Xuru Tso area, central Lhasa Terrane, select the host granites and dioritic enclaves and carry out a systematic petrography, zircon U-Pb gepchronology and _Hf isotopes,whole rocks elements study, attempting to provide more evidence for petrogenesis, tectonic setting and deep process in the area.According to the result of zircon U-Pb LA-ICP-MS dating of the Xuru Tso batholith, the age of the host granite（155.1±0.7Ma） is identical to that of the dioritic enclave（155.7±0.7Ma）, implying that they were the products of coeval magmatic events. The host granitic rocks are metaluminous to slightly peraluminous and high K calc-alkaline I-type granites, enrichment in LILE and LREE, lack of HFSE, and negative zircon ε_Hf（t）（-16.6^-6.6） values, indicating that they were derived from antaxis of ancient lower crust materials. The dioritic enclaves are metaluminous calc-alkaline and are characterized by negative zircon ε_Hf（t）（-8.9^-3.8） values, indicating that these enclaves were likely derived from partial melting of the ancient enrichment lithospheric mantle materials.Together with the published datas of the magmatic rocks of other areas of the central and northern Lhasa Terrane, this paper attempts to draw the conclusion that the granitoids from Xuru Tso area were formed by the varing extents mixing of mantle materials-dirved melts and crust-derived silicic melts from ancient basement of the central Lhasa Terrane in response to southward subduction beneath Lhasa Terrane of Bangong-Nujiang Ocean seafloor in Middle-Late Jurassic. And also, we believe that the coeval magmatic rocks of other areas of the central and northern Lhasa Terrane are the products of Bangong-Nujiang Ocean seafloor’s southward subduction.