东天山企鹅山群火山岩地球化学特征及其地质意义

Geochemical and Sr-Nd Isotopic Characteristics of the Volcanics from the Qi'eshan Group in Eastern Tianshan and Its Implications

根据主量元素、微量元素和Sr-Nd同位素地球化学研究结果,觉罗塔格构造带中企鹅山群火山岩企鹅山群火山岩分为拉斑玄武岩和钙碱性玄武岩,拉斑玄武岩和钙碱性玄武岩均具有高铝、低钛和相对富集轻稀土元素(LREE)、大离子亲石元素的特征,与典型的岛弧玄武岩相似。钙碱性玄武岩具有显著的Eu的负异常,其不相容元素含量显著高于拉斑玄武岩,在La/Sm-La图解中,钙碱性玄武岩为结晶分异作用的产物,拉斑玄武岩则为平衡部分熔融的产物。Sr-Nd同位素特征表明企鹅山群火山岩源自亏损地幔。在玄武岩构造环境判别图中样品均落入岛弧玄武岩范围内。通过综合该区岩石组合特征、地球化学特征、地球物理特征,认为企鹅山群为康古尔洋壳向北俯冲在大南湖岛弧南侧形成的石炭纪岛弧火山岩。

Based on the geochemical data including major elements, trace elements and Sr-Nd isotopes of the volcanics from Qi＇eshan Group occurring in the Jueluotage tectonic belt in eastern Tianshan, the volcanic rocks can be divided into theoleiitic series and talc-alkaline series. All of these volcanics show relative enrichment in aluminium, LREE, LILE and depletion in titanium. The calc-alkaline basalt has a characteristic of Eu anoma- lies, and the contents of incompatible trace elements are higher than those of the tholeiite basalt. The calc-alka- line basalt is the product of crystallization differentiation, and the tholeiite basalt is the product of partial melting from the La/Sm-La diagram. Initial Sr and Nd isotopic compositions show that the basahs from the Qi＇eshan Group are derived from depleted mantle. In the discrimination diagram, samples from the Qi＇eshan Group are plotted in the field of island are basalt. The characteristics of the rock combination, geophysics, geochemistry, and the results of previous studies suggest that Qi＇eshan Group formed in Dananhu island arc setting owing to the northward subduction of the Kanggur ocean