Zircon U-Pb age, Hf isotope, petrogeochemical characteristics and tectonic significance of the I type granites in the middle part of Xiemisitai Mountain in West Junggar

Jigentai is in the middle part of western Junggar. The authors found a set of Late Devonian granites surrounded by middle stage Variscan granite. The LA-ICP-MS zircon U-Pb age is 364.0±6.0Ma, suggesting Late Devonian granite which was discovered for the first time in this area. The lithology is composed of hornblende quartz monzonite and hornblende diorite. The rock has lower TiO₂ (0.49%~0.54%), relatively higher Al₂O₃ (16.09%~16.74%), and higher total alkali content (7.07%~8.52%), and has rich sodium. The distribution curve of rare earth elements shows a steep and moderate right-inclined curve, with relative enrichment of large ion lithophile elements Ba, K, Sr and high field strength elements Zr, Hf, Sm but relative depletion of high field strength elements Nb, Ta, P, Ti. The rock has a positive ε_Hf(t) (6.09~-12.91). The geochemical and mineralogical characteristics of the rock indicate that the rock mass is an island-arc type and I-type granite, and the source rock might have been partially melted from the material of the shear zone between the subduction plate and the lithosphere at the bottom of the island arc, and was in the process of ascending. It was contaminated by the upper crust. The discovery of the Late Devonian Island Arc Type I-granite in this area reveals the successive connection of the ocean basin stage, the subduction and accretion stage and the post-collision stage.