Mechanism of Formation of Premian Volcanic Rocks in Sawu′er Region, Xinjiang, China: Constraints from Rare Earth Elements

A large quantity of Premian volcanic rocks formed in Sawu′er region of Xinjiang, China. Based on the analysis of the rare earth elements′ (REEs) geochemical characteristics of the volcanic rocks, the correlativity of REE and major elements, and diagrams of covariant relation of REE, combined with the research results of the regional geological setting, petrology, and petrochemistry characteristics, it is inferred that the mechanism of the formation of Premian basic and intermediate volcanic rocks is mainly attributed to equilibrium partial melting, and the magmatic fractional crystallization is not significant, whereas the rock-forming processes of medium-acidic volcanic rocks is influenced by both partial melting and fractional crystallization. The REE geochemical research provided important evidence for the mechanism of magmatism of the Premian post-collision stage and the geodynamical evolution process.