岩鉱
Online ISSN : 1881-3275
Print ISSN : 0914-9783
ISSN-L : 0914-9783
青麻-恐火山列,陸奥燧岳,恐山,七時雨および青麻火山のK-Ar年代
東北日本弧第四紀火山の帯状配列の成立時期
伴 雅雄大場 与志男石川 賢一高岡 宣雄
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ジャーナル フリー

1992 年 87 巻 2 号 p. 39-49

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New K-Ar ages of four volcanoes; Mutsu-Hiuchidake, Osoreyama, Nanashigure, and Aoso volcanoes are presented. All of which are located in the Aoso-Osore volcanic zone along the Quaternary volcanic front of the Northeast Japan arc, and characterized by relatively low-K contents.
The obtained ages are as follows: 0.73±0.05 Ma for Mutsu-Hiuchidake, 0.74+0.06, 0.81±0.05 Ma for Osoreyama, 0.96±0.09, 1.06±0.07 Ma for Nanashigure, and 0.38±0.04, 0.40±0.02, 0.38±0.03, 0.38±0.04, 0.38±0.05 Ma for Aoso volcano.
Lateral and temporal variation of silica-normalized potassium contents (SiO2=57.5%) of the rocks from volcanoes, which are distributed in the volcanic front side during the past 4 m. y., is investigated. Lavas with relatively low potassium content have erupted continuously during past 4 m.y. in the whole area, whereas lavas with relatively high potassium content have erupted from volcanoes of the Sekiryo zone with ages younger than 0.7-1.0 Ma which is the formation age of the present volcanic zonation.

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