Petrogenesis of I -type garnet-bearing granite in the Yangbajing area within the Gangdese Batholith, Tibet

High silica granites ( HSGs) are common to large granitic batholiths worldwide. It is important for understanding crustal anatexis during arc magmatism and the evolution of continental crust. Within the Gangdese batholith, field observations and zircon U-Pb dating reveal a suite of HSGs occurred in the Yangbajing area, which formed at 64.9 +/- 0. 3Ma similar to 64. 1 0. 3Ma. Here, the petrographic, mineralogical, whole -rock geochemical and isotopic composition were carried out on the Yangbajing granite, and the results show that: (1) it belongs to the high -K calc-alkaline series, with high content of SiO2 and K2O, but low MgO, MnO, CaO and P2O5, and a gull -like REE pattern, and strong negative Eu anomalies, and enrichment in K, Rb, Pb, Th and U, and depletion of Nb, Ti and P; (2) magmatic garnets with almandine and spessartite significant enrichment in HREE, Sc, Y, and Zn, attributed to strong fractional crystallization of plagioclase; (3) fractional crystallization of plagioclase with high An components has also resulted in the decrease of Al/NK ratio in the evolved magma, which increased the solubility of zircon; and (4) zircon Hf and whole rock Nd isotopic compositions show enrichment characteristics (epsilon(Hf)(t) = -17. 1 similar to -11. 7; epsilon(Nd) ( = - 9. 0 similar to - 7. 6), suggesting that the melting of ancient crust magmatic materials and then underwent strong fractional crystallization, leading to the formation of I -type garnet -bearing granite.