Sandstone composition and tectonics in East Asia mobile belt

该项目的目的是了解东亚活动带砂岩的成分特征，并阐明其与活动带构造背景、盆地情况、气候和沉积环境的一般关系。Kiminami等人提出的Al_2O_3/SiO_2-碱度指数图。(1992)及其类似的K/Al-(Fe，Mg)/Al图解已被开发出来，作为了解沉积盆地古构造背景的工具。在日本群岛二叠纪至白垩纪积累了系统的砂岩成分资料。在该项目的控制下进行了380次化学分析。利用重矿物组合和石榴石、尖晶石、角闪石、斜长石等碎屑矿物的化学成分，从不同时代和构造背景的关键建造中提取了准确的生油岩信息。对近井地区第四系沉积物进行了碎屑石英同位素特征研究。此外，还从韩国锡霍特-阿林、菲律宾、澳大利亚东部和新西兰收集和积累了Abundact和高质量的砂岩数据。这些资料有助于阐明从古生代到现代的环太平洋构造运动。对白垩系埃佐组和古近系奥陶系泥川组浊积岩进行了水力分馏，认为砂粒粒度控制的成分差异在砂粒组内并不严重，但砂泥之间的差异是关键的。水力分馏在Al_2O_3/SiO_2-碱度指数图上清楚地显示出来。成分变化还受沉积环境、海平面高低、海侵或海退等沉积条件的控制。这些例子通过这个项目得到了澄清。这些基础研究提高了基于砂岩成分的古构造环境的精确重建。

The purpose of this project is to know the compositional characteristics of sandstones in the East Asia mobile belt and to clarify their general relationship to the tectonic setting, basin situation, climate and sedimentary environments in mobile belt. Al2O3/SiO2-Basicity Index diagram proposed by Kiminami et al. (1992) and its similar diagrams such as K/Al-(Fe+Mg)/Al diagram have been developed as a tool to know ancient tectonic setting of sedimentary basins. Systematic data of sandstone composition were accumulated for the Permian to Cretaceous in the Japanese Islands. 380 chemical analysis were performed under the control of this project . Heavy mineral assemblage, and chemical composition of detrital minerals such as garnet, spinel, amphibole and plagioclase have been used to detect precise information of source rocks from the key formations of various ages and tectonic setting. Isotope characterization of detrital quartz was tried for the Quaternary sediments of the Kinki district. Abundact and high quality data of sandstones were gathered and accumulated also from Sikhote-Alin, Korea, Philippine, eastern Australia and New Zealand. These data enable to clarify the Circum-Pacific tectonic movement from Paleozoic to Recent. Hydraulic fractionation was checked for turbidites of the Cretaceous Ezo Group and Paleogene Otoanshigawa Group, and concluded that compositional difference controlled by grain size is not serious within sand-size fraction but critical between sand and mud. Hydraulic fractionation is clearly shown on the Al2O3/SiO2-Basicity Index diagram. The compositional variations are also controlled by sedimentary conditions such as sedimentary environments, high stand or low stand of sea-level, and marine transgression or regression. These examples were clarified by this project. These basic researches improve the precise reconstruction of ancient tectonic setting based on sandstone composition.