早元古陡岭群变质杂岩的岩石地球化学特征

The Geochemical Features of the Douling Metamorphic Complex

河南省淅川县大陡岭至西峡县田关一带分布的陡岭群变质杂岩，由角闪岩相的变质岩石组成，主要包括片麻岩、钙硅酸粒岩、斜长角闪岩，夹少量的大理岩、石墨片岩和极少量的石英岩。岩石地球化学特征表明：片麻岩的原岩为一套泥砂质的沉积碎屑岩，具有后太古沉积岩的组成特点，形成于活动大陆边缘环境；透辉石变粒岩的原岩为钙砂质的沉积碎屑岩，但可能与片麻岩有着不同的物源区；斜长角闪岩有明显不同的两种产出状态和不同的两类稀土模式，一类呈夹层状与片麻岩互层产出，总稀土含量较低和不强的轻重稀土分离，原岩为非大洋型的拉斑玄武质火山岩；另一类则呈透境状产出，并具有很高的总稀土含量和强的轻重稀土分离，及明显的Ｅｕ负异常，原岩为拉斑玄武质的深成侵入岩。陡岭群变质杂岩有与秦岭群类似的岩石组合、原岩建造和时代等特征，形成于非大洋的活动大陆边缘环境。

The Douling Metamorphic Complex (the Douling Group) occurs as a early Proterozoic tectonic block in Qinling orogenic belt, being distributed in Xixia--Xichuan area, Henan Province, which mainly consists of metamophic rocks of amphibolite facies that include gneisses, Di-leptites and amphibolites.The gneisses have the mineral assemblage of PI+Bi+Mus +Q±Grt±Grph. Their original rocks are peliticarenaceous sedimentary rocks. The gneisses exhibit broadly the chemical feature of many post-- Archean sedimentary rocks and are considered to be formed in active continental margin. The Di--leptites are of low Al2O3,TiO2 andhigh CaO, MgO, and especially high CO2, with obviously lower TREE contents (62. 32-- 106μg/g),and a little higher LREE/HREE ratio. Its original rock is calc- arenaceous sedimental clastics. The amphibolites occur as two types: type Ⅰ is bedded to laminated and fine--grained, type Ⅱ is massive and coursegrained. They have similar major compositions, and are enriched in LIL and depleted in HSF elements, but their REE patterns are quite different. The type Ⅱ is significantly higher in LREE and has variable but more obviously negative Eu anormalies than the type Ⅰ, which indicates that they have different sources and different forming conditions. The regional setting, rock association, geochemistry and age of the Douling Metamorphic Complex can be compared with those of the Qinling Metamorphic complex and may belong to a part of the latter. Both of them formed in the active continental margin probably at the south margin of the North China Platform.