長門構造帯産花崗岩類および美禰層群産花崗岩質岩礫のK-Ar年代値とその地質学的意義
1977 年 72 巻 7 号 p. 277-287
詳細
1977 年 72 巻 7 号 p. 277-287
K-Ar ages were determined on the micas in the granite from Nagato Tectonic Zone and granitic pebbles in the Upper Triassic Mine Group whose distribution is shown in Fig. 1. The age of 371 m. y. obtained on the granite from Nagato Tectonic Zone is slightly younger than those of ortho-gneisses and amphibolite in the same area. This is suggestive of the emplacement of the granites successive to the regional metamorphism in this zone. On the other hand, the granitic pebbles in the Mine Group show the age (170 and 206 m. y.) similar to those of the Hida metamorphic and granitic rocks. The similarity in the modal and chemical compositions, and triclinicity of constituent potash feldspars is also recognized. This indicates two stages of regional metamorphism accompanied by plutonism in the Nagato Tectonic Zone.
