高级检索

    秦岭旬阳盆地下古生界钠长石岩岩石学和地球化学特征

    Geology and geochemistry of Lower Paleozoic albitite in the Xunyang basin, South Qinling

    • 摘要: 提要:热水沉积钠长石岩在南秦岭上古生界中颇具特点,与南秦岭众多的大型、超大型铅锌成矿关系密切。最近,在南秦岭旬阳盆地下古生界铅锌矿集区内的志留系梅子垭组地层中首次识别出一条近东西方向延伸长达10余千米的钠长石沉积岩带,与地层整合产出,渐变过渡,厚层块状、条带状、角砾状构造,均粒微-细晶结构、内碎屑结构;其化学成分以富含SiO2、Al2O3及Na2O为特征,富Fe、Mn,贫Co、Ni、Cu等微量元素;该钠长石岩的∑REE、LREE、HREE均较围岩偏低,具明显Eu亏损的特征。球粒陨石标准化配分曲线为右倾曲线。通过与秦岭泥盆纪热水沉积钠长石岩的岩相学及岩石化学对比,结合本区下古生界属于扬子北缘被动陆缘裂谷环境,初步认为这里下古生界钠长石岩可能属于热水沉积成因。

       

      Abstract: Abstract:Hydrothermal sedimentary albitite in the Upper Paleozoic in the South Qinling is closely related to many large-superlarge lead-zinc deposits in the south Qinling orogenic belt. Recently, a nearly E-W-striking, over 10 km long albitite zone has been recognized for the first time in the Lower Silurian Meiziya Formation in a Lower Paleozoic lead-zinc ore deposit concentration area of the Xunyang basin, South Qinling. It shows a conformable contact and gradational relationships with the country rocks and has thick-bedded and massive, banded, brecciated structures and fine and very fine equigranular and intraclastic textures. It is chemically characterized by enrichment in SiO2, Al2O3 and Na2O and is rich in the trace elements Fe and Mn and poor in the trace elements Co, Ni and Cu. Its ∑REE, LREE and HREE are lower than those of the country rocks and exhibit pronounced Eu depletion. The chondrite-normalized REE distribution patterns are inclined to the right. In comparison with the petrography and petrochemistry of hydrothermal sedimentary albitite in the Devonian of the Qinling, combined with the fact that its Lower Paleozoic belongs to a passive continental-margin rift environment on the northern margin of the Yangtze plate,the authors think that the Lower Paleozoic albitite in question is probably of hydrothermal sedimentary origin.

       

    /

    返回文章
    返回