Geochronological and Geochemical Characteristics of the Mesoproterozoic A-type Granite in the Western Yangtze Block and its Tectonic Implications

In order to elucidate the characteristics of the Mesoproterozoic tectonic evolution of the western margin of the Yangtze Block, this paper carried out systematic studies of zircon LA-ICP-MS U-Pb dating, whole rock geochemistry and Sr-Nd isotope analyses on the granite exposed in the Julin area of the western margin of the Yangtze Block. LA-ICP-MS zircon U-Pb geochronological results show that two representative granite samples give formation age of 1063±9 Ma and 1064±6 Ma, respectively. The whole-rock geochemical results show that the Julin granites are characterized by high Si and K, low Mg, Ca, P and Ti. The average A/CNK is 1.37, indicating a high-potassium calc-alkaline peraluminous series. The REE patterns show a right-leaning "seagull" type, with negative Eu anomalies. They are enriched in high field strength elements (e.g., Zr, Th and Hf) and large ion lithophile elements (e.g., Rb and K), and depleted in Ba, Sr, P and Ti. They show enriched Nd isotope compositions with εNd(t) values from -9.90 to -4.53. The above results indicate that the Julin granites were formed in the late Mesoproterozoic and exhibit geochemical characteristics similar to those of A-type granites. Comprehensive studies suggest that the Julin granites were derived from partial melting of old continental crust. They were formed in a post-collisional or post-orogenic extensional environment, which is closely related to the aggregation of the Rodinia supercontinent. © 2021, Science Press. All right reserved.