新疆和硕县乌什塔拉红山花岗岩岩浆起源及成因机制

红山花岗岩体位于新疆南天山乌什塔拉乡以北,乌瓦门-拱拜子和辛格尔两大区域性大断裂中间;岩石类型主要为二长花岗岩,其次为花岗闪长岩;SiO2含量为61.95%~76.37%,全碱(ALK)含量较高,为6.35%~8.3%,绝大部分具有高K钙碱性花岗岩的特征。A/CNK值为0.94~1.08,属于准铝质-弱过铝质花岗岩类;∑REE=137×10-6~244.5×10-6,LREE/HREE为4.1~6.7,表明LREE明显富集,δEu为0.14~0.27,显示出中等程度的Eu负异常。大离子亲石元素K、Rb及高场强元素Zr、Hf、Th相对富集,而Nb、Ta、P、Ti等相对亏损。锆石 U-Pb SHRIMP同位素年龄为297±3 Ma(待发表数据)。综合分析地球化学特征,认为其可能来自于石榴子石稳定的深部地壳,源区有相当比例的黑云母,最合适源区物质可能是碱性和高K钙碱性的安山岩和玄武质安山岩。地幔岩浆的低侵作用可能是导致下地壳物质部分熔融的主要原因。结合区域地质背景及微量元素投图分析,认为岩浆形成于从挤压环境向伸展环境转变的碰撞-后碰撞造山期。

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 The Zircon U-Pb SHRIMP isotope age is 297±3 Ma(unpublished data).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.