Redetermination of the volcanic eruption time and analysis of geochemical characteristics of volcanic rocks in eastern Maotoushan of Beishan area, Xinjiang

Abstract：The field geological features, petrology, lithogeochemistry and high degree of accuracy isotope chronology of volcanic rocks in eastern Maotoushan of Beishan area, Xinjiang, are discussed in this paper. The rock association of this area is composed of basalt, basaltic andesite, andesite and tuff with the same components. U-Pb isotope SHRIMP dating shows that the eruption time of volcanic rocks should be Lower Permian. The volcanic rocks are of the calc-alkaline series. No obvious REE fractionation and clear negative Eu anomalies are observed, and there exist enrichment of Rb, Th and U, slightly fluctuation of Ba, Sr, and loss of Nb, Ta. An integrated analysis led the authors to believe that the early Permian volcanic rocks were formed in a fully shrunk residual sea basin environment, and the structural attributes at that time were similar to features of the epicontinental volcanic basin of the residual sea basin instead of having the characteristics of the rift.