飛だ変成帯の角せん石のＫ‐Ａｒ年代

Abstract

K-Ar ages have been determined on hornblendes from seven metamorphic rocks and two Funatsu Granitic Rocks from the Hida Metamorphic Belt. The ages of metamorphic rocks range from 174 to 223 m.y., and grouped into two: about 220 m. y. and 175-195m.y. The former ages represent the time of the main metamorphism in the Hida Metamorphic Belt, whereas the latter may have resulted from rejuvenation by the intrusion of the Funatsu Granitic Rocks or from slow cooling. An age or 180m.y. is obtained on hornblende from the Shimonomoto type of the Funatsu Granitic Rocks, and it confirms the time of intrusion for the Funatsu Granitic Rocks. Hornblende from augen gneiss, gives an age of 213m.y., which is similar to that of hornblendes from the Hida Metamorphic Rocks, thus suggesting that the augen gneiss is genetically different from the typical Funatsu Granitic Rocks. It is interpreted that hornblendes dated here contain no excess argon.