Sandstone Composition in Mobile Belt : An Example from Japanese Islands

对研究结果进行如下总结：采用化学分析方法研究了白垩系Hidaka超群、北上北带侏罗系、侏罗系Tanba群、白垩系-古近系Shimanto超群、超Tanba带二叠纪、舞津带三叠纪、白垩系Izumi群、Chichibu带二叠纪、thenkai海槽等岩心样品的砂岩和砂岩。研究揭示了日本主要盆地碎屑岩的化学特征，以及各地质时期砂岩化学成分的鲜明特征。研究还得出了岩浆弧类型与砂岩化学特征之间的关系。对多个盆地的砂岩进行了模态分析，揭示了砂岩组成的时代特征。(1)日本西南部内带和秩父带二叠系砂岩主要属于缺乏石英的中间火山砂岩相。(2)大岛带、北北上带、米诺带、坦巴带和赤父带侏罗系砂岩属富石英花岗质砂岩相。(3)白垩纪砂岩模态组成具有区域性差异。石曼托、叶左、希达卡等欧亚边缘盆地的砂岩属于富石英-缺石英、酸性-中酸性火山砂岩相。

The following summary of the research results is obtained.1. Sandstone and sands from the Cretaceous Hidaka Supergroup, Jurassic of the northern Kitakami Belt, Jurassic Tanba Group, Cretaceous-Paleogene Shimanto Supergroup, Permian of Ultra-Tanba Zone, Triassic of the Maizuru Belt, Cretaceous Izumi Group, Permian of the Chichibu Belt, core samples from thenkai Trough and others were studied by means of the chemical analysis. The studies have revealed chemical features of clastics from the staple basins in Japan, and a distinctive character of chemical composition of sandstones in each geologic time. The studies also have resulted in the relation between the type of magmatic arc and chemical features of sandstone.2. Modal analysis of sandstones from many basins has revealed the character of times on sandstone composition.(1) Sandstones from the Permian in the inner belt of southwest Japan and in the Chichibu Belt belong predominantly to a quartz-deficient intermediate volcanic sand petrofacies.(2) Sandstones from the Jurassic in the Oshima Belt, northern kitakami Belt, Mino Belt, Tanba Belt and Chichibu Belt belong to a quartz-rich granitic sand petrofacies.(3) Cretaceous sandstones show regional variation in modal composition. Sandstones from such basins situated on the Eurasian margin as Shimanto, Yezo and Hidaka belong to quartz-rich to quartz-deficient, acidic to intermediate volcanic sand petrofacies.