Zircon U-Pb ages, genetic evolution and geological significance of Carboniferous granites in the Harlik Mountain, East Tianshan, Xinjiang

Extensively developed granitoids in northern Xinjiang have constituted one of the hotspots in the study of granite in the western Central Asian Orogenic Belt. LA-ICP-MS zircon U-Pb analysis of the Xiaopu biotite monzogranite and Qinchengnan hornblende monzogranite in the Harlic area yielded crystallization ages of 316±4Ma and 320±3Ma. Their petrological and geochemical characteristics show that Xiaopu pluton belongs to high-K calc-alkaline and weakly peraluminous series of I-type granite, whereas the Qinchengnan pluton belongs to high-K calc-alkaline and metaluminous series with A-type granite characteristics. The Xiaopu pluton has positive zircon ε_Hf (t) values of +8.0~+13.8, and the Qinchengnan pluton has higher ε_Hf (t) values up to +10.8~+16.7, with corresponding Hf model ages (T_DM^c) of 822~450Ma and 641~268Ma, respectively. These isotopic compositions indicate that young crust served as the main source of the granite generation. Combined with coeval basic rocks with similar isotopic compositions in this region, it can be believed that these young granites might have been related to the new mantle-derived basic magma underplating and exhibited the post-collision vertical growth. Additionally, the Qinchengnan granites have A-type granite characteristics, thus providing a further evidence for the transition period of Late Carboniferous from collision to post-collision settings.