Zircon U-Pb geochronology and Hf isotopic geochemistry of Jiangba,Bangba,and Xiongba granitoids in western Gangdese,Tibet

The study on the Mesozoic granitoids in the western Gangdese belt is still limited.This paper presents the zircon SHRIMP U-Pb dating and Hf isotopic results on the Jiangba,Bangba,and Xiongba granitoids.The results are also applied to the discussion of the granitoids distribution as well as the nature of the crustal basement from which the granites originated.The ages of the Middle-Late Jurassic Jiangba granodiorite and Xiongba alkali granite are 170±3Ma and 149±3Ma,respectively.The ages of the Bangba orthogranite and its quartz monzodiorite enclaves are 144±3Ma and 133±3Ma,respectively,suggesting the Early Cretaceous magmatism.The Hf isotopes(eHf(t))and Hf crustal model age of the Middle-Late Jurassic Jiangba(-16.8~-13.4 and 2.1~2.3Ga)and Xiongba(-11.3~-6.2 and 1.6~2.0)granitoids are similar,which indicates an enriched,Paleoproterrozoic crustal basement under the study areas.The Early Cretaceous Bangba intrusive(eHf(t)=-4~-0.8,model age=1.2~1.5Ga)and the dioritic enclave(eHf(t)=-2.8~+0.6,model age=1.2~1.4Ga)have similar features,suggesting the magma mixing event during their forming processes.The result in this paper further implies that the Paleoproterrozoic crustal basement has involved in the reworking of the Mesozoic magmatism,although they have not been revealed on the surface.