Sandstone composition and tectonics in East Asia mobile belt

本项目的目的是了解东亚活动带的砂岩组成特征，阐明其与活动带的构造背景、盆地形势、气候和沉积环境的一般关系。Kiminami等（1992）提出的Al2O3/ sio2 -碱度指数图及其类似的K/ al -(Fe+Mg)/ al图已被发展成为认识沉积盆地古构造背景的工具。积累了日本列岛二叠系至白垩系砂岩组成的系统资料，在本项目控制下进行了380次化学分析。利用榴石、尖晶石、角闪洞、斜长石等碎屑矿物的重矿物组合和化学成分，从不同时代和构造背景的关键地层中获得了精确的烃源岩信息。对近基地区第四纪沉积物进行了碎屑石英同位素表征。在锡霍特-阿林、韩国、菲律宾、澳大利亚东部和新西兰等地也收集和积累了大量高质量的砂岩资料。这些资料有助于厘清古生代至近代的环太平洋构造运动。对白垩系埃佐组和古近系Otoanshigawa组浊积岩进行水力分馏，认为粒度控制的浊积岩在砂级段内成分差异不严重，但砂泥组分差异较大。水力分馏在Al2O3/ sio2 -碱度指数图上清晰地显示出来。沉积物成分的变化还受沉积环境、海平面高低、海侵或海退等沉积条件的控制。本项目对这些例子进行了澄清。这些基础研究提高了基于砂岩成分的古构造背景精确重建。

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.