Petrogenesis of Daxiong pluton in western Gangdese, Tibet: zircon U-Pb dating and Hf isotopic constraints

LA-ICP-MS zircon U-Pb age,whole-rock major and trace element,Sr-Nd and zircon Hf isotopic compositions from the Daxiong pluton,western Gangdese are used to constrain its origin.The predominant lithology observed in Daxiong pluton is granodiorite,in which diofitic enclaves are well developed.Zircon U-Pb dating for one granodiorite sample yields an emplacement age of 107±1Ma.Zircon Hf isotopic analysis yieldse_(Hf)(t) values of - 1.0 to +3.0,with two-stage model age ranging from 974 to 1226Ma.Granodiorites are silica enriched in composition (SiO_2=70.65%～71.10%),with high contents of CaO (3.21%～3.26%) and low contents of K_2O(2.81～2.99%) and P_2O_5(0.09%).Both granodiorite and dioritic enclave are medium-K calc- alkaline,and exhibit similare_(Nd)(t) values (-4.6,and -3.2,respectively).Their two-stage model ages are identical,consistent with the zircon Hf isotope model age.Geochemical characteristics combined with field and petrographic observations show that the dioritic enclave can be considered as the mafic microgranular enclave.Our data indicate that an important magmatic mixing event probably occurred in middle-western Gangdese belt during the late of Early Cretaceous time.