| Abstract |
Glaucophanitic metamorphic rocks are exposed limitedly in the Kiyama district, about 10 kilometers east of Kumamoto City. These rocks are overlain unconformably by the Mifune group of Cretaceous age o...n the southern side. They consist mainly of prominent basic rock with interbeded sandstone and shale, and about 1500 meters in thickness. The Kiyama metamorphic rocks trend NEE direction and generally dip to the north at high angle. The grade of metamorphism increases regularly toward the upper horizon. Based on the distribution of some minerals, this district is divided into two zones; Zone I: quartz, albite, epidote, chlorite, actinolite, calcite, muscovite and glaucophane. Glaucophane is confined to the basic rock. Zone II: quartz, albite, epidote, chlorite, actinolite, calcite, muscovite, garnet, tourmaline, biotite, and hornblende. Incipient biotite, garnet and hornblende are stable in the pelitic rcck. This zone is also characterized by the occurrence of large spotted albite. Actionolite and epidote are stable in all. These two zones are correspondent from upper part of the glaucophane schist fades to the lower part of the epidote amphibolite facies, respectively. From the recent K-A age determination using muscovite, the metamorphism took place in Carboniferous in age. This result indicates that the metamorphic rocks in question are the oldest ever known by absolute age in Japan. But this must carefully be investigated. The relation of the metamorphic rocks of this district with those of the Sanbagawa metamorphic zone is discussed.show more
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