On the Significance of the Gneissic Rocks Found as Xenoliths in Andesite on the Sangun Metamorphic Belt of Yamaguchi Prefecture

Gneissic rocks are found as xenoliths in the andesite of Mitakésan (Kimpôzan), 15 km to the north-northeast of Tokuyama City, Yamaguchi Prefecture. The xenoliths consist mainly of gneisses derived from basic rocks, containing hornblende, biotite, and plagioclase, in some specimens with clinopyroxene. Quartzo-feldspathic gneisses, consisting of biotite, plagioclase, and quartz, sometimes with garnet, pelitic gneiss, and non-foliated magmatites are also included. Judged from their rock association and mineral assemblage, they cannot be correlated to the gneisses either of the Ryôké or the Sangun metamorphic complex. The occurrence of gneiss xenoliths testifies to the presence of sialic layer, underlying the Sangun crystalline schists, which are characterized by the nature of the glaucophanitic metamorphism.