Geochemistry and petrogenesis of Jurassic granites in Nyemo area, South Lhasa terrane, Tibet

The Gangdese batholith is an important magmatic record of the northward subduction of the Neo-Tethys Ocean and the Indian -Eurasian collision, and Nyemo is located in the middle of the Gangdese batholith. In this paper, we report the zircon U-Pb geochronology, element geochemistry and zircon Hf isotopes of the host granites and gabbroic enclaves from Nyemo area. Zircon U-Pb dating results show that both the host granites ( 197 190Ma) and enclaves ( 195Ma) were formed in the Early Jurassic, and they should be emplaced at the same time. The host rocks are slightly peraluminous and high K calc-alkaline granites, which enriched light rare earth elements such as K, U and Sr, and depleted high field strength elements such as Nb, Ta and Ti. Their zircon e,(t) values varied within the range of + 13. 9 + 16. 0, indicating they may have been derived from partial melting of the juvenile crust. The gabbroic enclaves are metaluminous calc-alkaline rocks with rare earth elements and trace elements distribution characteristics similar to the host rocks, and their zircon EHf( t) values are within + 13. 8 + 16. 0, showing that they may represent the juvenile lower crust formed in the Jurassic, which is the magmatic source of the host rocks. Based on previous studies, we suggest that the host granites and enclaves in Nyemo may be related to partial melting of mantle and juvenile crust caused by the northward subduction of the Neo-Tethys Ocean.