内蒙古大苏吉地区埃达克质花岗岩地球化学特征及其地质意义

Geochemical characteristics and geological significance of adakitic granite in Dasuji,Inner Mongolia

大苏吉花岗岩体位于内蒙古中部东西向白云鄂博-赤峰花岗岩带上,主量元素分析显示：富硅,铝碱质量分数偏高,相对富钠贫钾,贫钙、镁,岩浆分异演化程度高,属过铝质钙碱系列岩石.稀土和微量元素分析显示：稀土元素富集程度低,轻稀土相对富集,重稀土相对亏损,δ（Eu）=1.28~6.58,呈w（Eu）正异常.w（Sr）高,w（Y）、w（Yb）低,w（Sr）/w（Y）高,大离子亲石元素K、Th、Rb、Ba、Sr等富集,高场强元素Ta、Nb、Y、Yb等相对亏损,与典型的埃达克岩微量元素地球化学特征相似.综合分析表明,大苏吉地区埃达克质花岗岩可能是由俯冲的玄武质洋壳板片部分熔融形成的,埃达克质花岗岩的确定为探讨板块俯冲构造演化提供了新的证据,对深化该区成矿规律和找矿具有借鉴和指导意义.

The Dasuji granite rock bodies are located in the Baiyunebo-Chifeng granite belt in the east-west axis of the middle Inner Mongolia.The major element of rock samples showed that the rock bodies are characterized by rich silicon,high level aluminum and alkali,relatively rich sodium,poor potassium,calcium,magnesium and high degree of magmatic differentiation evolution,and they belong to peraluminous calcium alkali series.Based on the rare earth and trace elements analysis,the results exhibited a low-degree enrichment in rare earth elements,LUEE concentration,HREE deficit,δ（Eu）=1.28~6.58 with a positive w（Eu） anomaly.The content of w（Sr） is high and w（Yb）,w（Y） is low;w（Sr）/w（Y） is high and large ion lithophile elements K,Th,Rb,Ba,Sr are of a high level;highfield strength elements Ta,Nb,Y,Yb are relatively deficient,all of which features are similar to the trace element geochemical characteristics of typical adakite.An integrated analysis suggested that the adakite granite might have originated from the partial meting of the subducted basaltic oceanic crust plate.The confirmation of adakite can provide new evidence for discussing about the plate tectonic evolution and a very useful reference or guide to studying the metallogenic regularity and prospecting.