PETROLOGICAL STUDY CONCERNING ORIGIN OF PELITIC SCHISTS IN THE SANBAGAWA BELT

研究了三百川带绿泥石带泥质片岩的岩石化学和矿物学特征的多样性。A1203/Si02、Na20/K20、Mn0/Ti02对沉积环境的判断(Roser和Korsch，1986：Sugisaki，1984等)与片岩的碳、氮含量一起显示出很大的变化，这可能是由于环境的差异和变质过程中的部分化学作用所致。岩石学和矿物学研究表明，在一些泥质片岩中存在中压型变质成因的白云母、钠长石斜长石、石英、碳质物质以及可能的尖晶石(估计来自玄武岩)等碎屑矿物的产状。包括地质和岩石学研究在内的综合研究表明，原始岩石是细碎片状的(硅质层-片岩)，至少来自几个不同的盆地，如通常供应大陆碎屑的深海扇，以及通常供应大量基性火山碎屑岩的远洋或半深海深海盆地，以及与鞘褶皱形成、远洋浊积岩沉积有关的构造体制。它首先由Faure(1983)引入，并延伸到ASemigawa地区的绿泥石带。因此，桑巴加瓦带是一个由多个不同盆地形成的岩石组成的混合地体，并遭受了简单的剪切变形，这与推覆构造的形成密切相关。

Diversity of pelitic schists of the chlorite zone in the Sanbagawa belt in terms of their petrochemical and mineralogical featured was examined in the Asemigawa area, central Shikoku and some other places. A1203/Si02,Na20/K20,Mn0/Ti02, which are diagnostic for estimation of sedimentary environments (Roser and Korsch, 1986: Sugisaki, 1984 etc), show wide variation togehter with Carbon and Nitrogen contents for the schists probably due to diversity of the environments and partly chemical modification during the metamorphism. Petrographical and mineralogical studies reveal occurrences of detrital minerals such as muscovite of intermediate-pressure type metamorphics origin, albitic plagioclase, quartz, carbonaceous materials and probably spinel(estimated from fuchsite) in some of pelitic schists.Comprehensive examinations including geological and petrological studies suggest that original rocks was finely laminated(chert-laminite) and have derived from, at least, a few different basins such as a deep sea fan, where clastics of continent origin were commonly supplied, and a pelagic or hemi-plagic deeep sea basin where a large amount of mafic volcanicalastic rocks were commonly supplied and distal turbiditemay have been deposited.Deformation regime related to sheath fold formation, which was firstly introduced by Faure (1983), extended to the chlorite zone in the Asemigawa area. Thus, the Sanbagawa belt is an amalgamated terrane composed of rocks originated a few different basins, and suffered simple shear deformation which sebsequently related to nappe formation.