胶东变质超镁铁—镁铁质岩石的地球化学特征及地幔源区性质

本文以地球化学方法为研究手段,结合野外宏观地质特征,论述了胶东地区前寒武纪变质建造中超镁铁—镁铁质岩石的地球化学性质及其成因。研究结果表明,该区超镁铁—镁铁质岩石为地幔不同程度熔融的产物,超镁铁质岩石相当于科马提岩类;镁铁质岩石为拉斑玄武岩类,并按橄榄质科马提岩→玄武质科马提岩→拉斑玄武岩演化系列的化学组成表现出连续的变化趋势。 拉斑玄武岩中的微量元素(主要是稀土元素)地球化学特征表明,其形成环境与现代板块构造的典型火山(岛)孤或孤后盆地环境相类似,并反映出地幔源区具有“富集型”地幔的特点,且存在着地幔不均一性。

GEOCHEMICAL CHARACTERISTICS OF METAMORPHOUS ULTRAMAFIC-MAFIC ROCKS IN JIAODONG GROUP AND THEIR PROPERTIES IN THE MANTLE SOURCE AREA

This article has demostrated the geochemical and genetic characteristics of ultramaf-ic-mafic rocks, which distributed in the Precambrian metamorphous formation inJiaodong district, through the geochemical methods and the field geological observatlons.The studies showed that the ultramafic-mafic rocks were the partial melting products ofmantle materials. The ultramafic rocks are related to komatiite and mafic rocks related totholeiite. These rocks suggested that there was a evolutional series from olivine komatiitethrough basaltic komatilte to tholeiite and a continual changing tendency on the chemicalcomposition.The trace elements (mainly REE ) geochemistry of tholeiites shows that the rocks o-riginated from the typical volcanic (island) arc or back-arc basin environment in the opinionof modern plate tectonics, and that the source area of mantle had the characteristics of"enriched"~ mantle and the mantle was unhomogeneous.