LA-ICP-MS zircon U-Pb chronology, Hf isotopes and geochemistry of the Xinjie granites in western Yunnan and their implications

The Xinjie granite body is located in the north of the Changning-Menglian suture zone. The rock type is mainly monzogranite. LA-ICP-MS zircon U-Pb dating indicates that the Xinjie granite body was emplaced at about 82Ma of Late Cretaceous. The major element chemical data of the Xinjie granites show that SiO2 values vary from 74.28% to 75.17%, with high K2O (K2O/Na2O=1.44~1.73), low CaO (0.37%~0.41%) content, and A/CNK 1.10~1.22. The Xinjie granite body displays obvious enrichment of Rb, Th, K and LREE, and relatively negative anomalies of HFSE such as Nb, Ta, Ti, Zr and Hf. It is suggested that the Xinjie intrusion belongs to peraluminous S-type granite. The negative εHf(t) values are distributed in a wide range (-16.9~-0.5), which, together with ancient Hf-isotope crust model age (1.19~2.28Ga), indicates that the intrusion mainly originated from re-melted ancient crust materials with the addition of varying degrees of mantle materials. The partial melting was related to the subduction of Neo-Tethyan plate.