PETROLOGICAL STUDY CONCERNING ORIGIN OF PELITIC SCHISTS IN THE SANBAGAWA BELT

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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.