Geochemistry and petrogenesis of the Late Jurassic Xuru Tso batholith in central Lhasa Terrane

The Late Jurassic magmatism is spreading in the central Lhasa subterrane, but their petrogenesis remains poorly constrained. This study presents new zircon U-Pb age, whole rock geochemistry, and zircon Hf isotopic data for the host granite and dioritic enclaves from the Xuru Tso area. The zircon dating for the host granite yields U-Pb age of 155. 1 +/- 0. 7Ma, which is identical to that of the dioritic enclave (155. 7 +/- 0. 7Ma). The host rocks are metaluminous to slightly peraluminous and high K calc-alkaline I-type granites, showing enrichment of large ion lithophile elements and light rare earth elements relative to high field strength elements. Their negative zircon epsilon(Hf)(t) values (-16. 6 similar to -6. 6) indicate that they were derived from antaxis of ancient Lhasa terrane crust. The dioritic enclaves are metaluminous calc-alkaline and exhibit overall negative but significantly higher zircon epsilon(Hf) (t) values (-8. 9 similar to -3. 8) in comparison with the host granites, suggesting that these enclaves may document the input from mantle lithosphere. These observations indicate that the Late Jurassic granitoids from Xuru Tso were formed by the magma mixing between mantle-derived melts and crust-derived silicic melts originating from ancient crust beneath central Lhasa subterrane, and can be best explained as reflecting the southward subduction of Bangong-Nujiang Neo-Tethyan oceanic seafloor.