新疆苏海图地区火山岩地球化学特征及构造环境分析

Geochemical Characteristics and Tectonic Environment of Volcanic Rocks in Suhaitu Arear,Xinjiang

苏海图组火山岩发育自然铜矿化,具有从拉斑玄武岩系列向钙碱性玄武岩系列过渡的特点。依据地球化学特征,表明其TiO2含量较低(<1%),玄武岩高的Al2O3含量、低的稀土含量,并且稀土元素曲线具有平缓型到轻稀土低度富集的特点。微量元素原始地幔标准化图解上,它们均富集大离子亲石因素(LILE),亏损高场强元素(HFSE),具有强的Nb和Ta的负异常,Ti的低负异常,以及P和Sm的低正异常。Zr/Nb值和Sm/Nd值接近MORB的范围,Th/Nb值大于0.11,Nb/Zr值小于0.04。以上这些特征均显示出典型岛弧岩浆的特点。所以,苏海图组火山岩为火山弧火山岩,其构造背景为大陆岛弧,源区可能为被流体或沉积物交待改造的亏损地幔。

Native copper mineralization has been found in volcanic rocks of Suhaitu formation,with a feature of transition from tholeiite basalts to calc-alkaline basalts.Geochemistry shows that the volcanic rocks have lower TiO2content（less than 1%）,fewer Rare Earth Elements and high Al2O3content.In addition,their REE pattern is characterized by the weak enrichment of LREE.In the primitive mantle normalized trace element spider diagram,Suhaitu volcanic rocks are characterized by the enrichment of large ion lithophile elements,and deficit of the high field strength element.They have strongly negative anomalies in Nb and Ta,weakly negative anomalies in Ti,and weakly positive anomalies in P and Sm.Their Zr/Nb and Sm/Nd ratios are close to the range of MORB,the value of Th/Nb is larger than 0.11,while the Nb/Zr ratio is less than 0.04.All these characteristics mentioned above suggest that volcanic rocks of Suhaitu formation were typical volcanic arc rocks,their tectonic environment was continental island arc,and its magmas were generated by partial melting of the depleted mantle modified by fluids or sediments.