Geochemical Characteristics and Tectonic Significance of the Volcanic Rocks from Lower Triassic Huari Formation in West Qinling

The Huari Formation, located in Hezuo region of West Qinling, are mainly consist of neutral to acidic volcanic rocks, including dacite, andesite, volcanic breccia and tuff. The rock geochemical results show that, these rocks belong to calc-alkaline series, with the characteristics of high potassium and alumina, low alkali and titanium. Moreover, the geochemical features of these rocks on trace elements are similar with the ones of typical volcanic island arc. The total rare earth elements are 61.91×10^-6~185.58×10^-6, with an average of 128.04×10^-6, showing LREE enrichment, HREE depletion with weak negative Eu anomalies (average is 0.98). Combined with the tectonic evolution of western Qinling orogenic belt, it's suggested that lower Triassic Huari Formation was formed in island arc setting.