Magmatic Origin and Petrogenesis of Hongshan Granite in Wushitala, Heshuo County, Xinjiang, China

The Hongshan granite pluton is located in north Wushitala town, south of Tianshan Mountain, between Wuwamen-Gongbaizi and Xinge'er, the two huge regional fractures. The granite is composed mainly of monzonitic granites together with granodiorites. As to the chemical components, SiO₂ takes up 61.95%~76.37%, the Alkali content is relatively higher, with K₂O+Na₂O of 6.35%~8.3%. SiO₂ and K₂O values of most samples are plotted of high-K calc-alkaline granites. The A/CNK value of 0.94~1.08 shows that Hongshan granites belong to metaluminous-peraluminous type of granites. Hongshan granites are also characterized by higher REE gross of 137×10^-6~244.5×10^-6, LREE/HREE of 4.1~6.7, which indicates LREE obvious enrichment. δEu is 0.14~0.27, demonstrating moderate negative Eu anomalies. In addition,Hongshan granites are enriched in K, Rb(LILE) and Th, Hf, Zr(HFSE), and depleted in Ta, Nb, P, Ti, Sr, etc. The Zircon U-Pb SHRIMP isotope age is 297±3 Ma(unpublished data). According to the comprehensive analysis of the geochemical characteristics, these granites most likely come from lower crustal materials in the stable garnet field with a significant proportion of biotie. Alkaline and high-K calc-alkaline andesite and basaltic andesite may be the most suitable source material. The underplating or intraplating scheme may be the main reason of the partial melting of lower crustal materials. In combination with regional geological background and trace element diagrams of the tectonic settings, it is suggested that these high-K calc-alkaline granites were emplaced during the orogenic period of collision to post-collision when the compression environment is transformed to extension environment.