摘要
坦桑尼亚维多利亚湖绿岩带位于坦桑尼亚太古宙克拉通西北部,是重要的金成矿带。火山岩类型主要为变质镁铁质火山岩和变质长英质火山岩,具有双峰式火山岩特征。文章通过对维多利亚湖地区变质火山岩主量元素、微量元素及稀土元素的研究,了解了坦桑尼亚绿岩带构造演化环境和成岩机制。岩石地球化学特征表明:变质镁铁质火山岩属于钙性岩系列,源岩为亏损洋脊玄武岩幔源(DMM)物质和俯冲消减物质(SDC)的混合物;变质长英质火山岩呈高Na_2O/K_2O比值和高Al_2O_3含量,强烈的负Nb异常,重稀土元素含量低(Yb为0.24×10~(-6)~0.68×10~(-6))并有较强的分异作用,这些特征与典型的太古宙TTG岩套相似。该区熔岩具有洋中脊玄武岩和岛弧玄武岩地球化学亲和性特征,具有聚敛边缘构造背景,形成于太古宙弧后盆地。
The Victoria Lake greenstone belt in NW Archacan craton in Tanzania is an important gold-forming belt. The volcanic rocks mainly consist of metamorphic mafic volcanic rocks and felsic rocks,showing the characteristics of bimodal volcanic rocks.This paper presents a study of the volcanics from the Victoria Lake area on its major and trace elements to further understand the tectonic evolution.Petrogeochemical characteristics show that metamorphic mafic volcanic rocks represent a calcic rock series,which are a result of the interaction between DDM and SDC sources; metamorphic felsic rocks are characteristed by high Na2 O/K2 O ratios and Al2 O3,large negative Nb anomalies and low HREE contents leading to highly fractionated REE patterns.These characteristics are similar to typical of Archaean TGG suits ﹒ The lavas in this area show the mixture of MORB and arc-like geochemical affinities,presenting a convergent margin tectonic setting,which are formed in an Archaean back arc basin.
引文
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