Geoscience reports of Shimane University

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Geoscience reports of Shimane University 14
1995-12-25 発行


Protoliths of the metamorphic clasts from the Ohyamamisaki Formation within the Shimanto belt, Shikoku, Japan
Mabuchi, Emi
The conglomerates from the Ohyamamisaki Formation,located in the Shimanto belt,contain metamorphic clasts.On basis of their lithology and composition,these conglomerates can be divided into two different groups located in the northern and southern part of the Shimoyama area.
The main lithologies we can find in the clasts from the northemrn part are as follows : pelitic schists,including spotted schists,acidic tuff and basic schists.On the other hand,the clasts from the southern area can be identified as garnet-bearing siliceous pelitic schist fragments.
According to the chemistry of muscovite and garnet,these pelitic schists could be ascribed to the chlorite or garnet zone of the Sambagawa metamorphic belt.The garnets within the siliceous pelitic schists from the northern area are extremely rich in the spessartine component.The suggested route followed by these clasts is the following : Sambagawa metamorphic zone→(Mikabu greenstonebelt)→ Kurosegawa tectonict zone→ Shimanto belt.On the other hand,the clasts from the northern area are likely derived from the Kurosegawa tectonic zone.