米仓山西缘变质杂岩地质和岩石地球化学特征

THE GEOLOGY AND PETRO-GEOCHEMICAL FEATURES OF METAMORPHIC COMPLEX IN THE WESTERN MARGIN OF THE MICHANGSHAN

米仓山西缘变质杂岩由后河岩群和八角树片麻岩(Bgn)构成,而后河岩群又可分为河口变粒岩—斜长角闪岩(Hgnt-amp)、汪家坪变粒岩(Wgnt),构造样式表现,为卵形穹盆构造和韧性剪切带。岩石地球化学特征表明,河口变粒岩—斜长角闪岩的原岩为中酸性火山岩、拉斑玄武岩和杂砂岩,形成于洋-岛弧环境;汪家坪变粒岩的原岩为杂砂岩和中酸性火山岩,形成于大陆或大陆边缘环境;八角树片麻岩的原岩为英云闪长岩—奥长花岗岩—花岗闪长岩(TTG)岩套。因此变质杂岩应形成于早前寒武纪(晚太古宙—早元古宙)。

The metamorphic complex in the western margin of Michangshan consist of the Houhe Rock-Group the Bajiaoshu Gneiss and which is composed of Hekou granulitite amphibolite and the Wangiaping granulitite.The structural styles in the metamorphic complex are characterized by gneiss domes and basins as well as ductile shear zones.Rock geochemical characteristics reveal that the original rock of the Hekou granulitite and amphibolite were intermediate-acidity volcanics, tholeiite and greywacke formed in the ocean and island are ehvironment,and that original rocks of the Wangjiaping granulitite were greywacke and intermediate-acidity volcanics formed in the con- tinent or continental margin environment,that the original rocks of the Bajiashu gneiss were tonalite-trondhjemite-granodiorite(TTG)suite.The structural and rock geochemical characteristics indicate that the metamorphic complex was formed in Late Archean to Early Protorozoic.