黒富士火山と甲府盆地北方に分布する火山岩類の火山活動とK-Ar年代
1994 年 89 巻 1 号 p. 15-20
詳細
1994 年 89 巻 1 号 p. 15-20
Kurofuji Volcano occupies the northwestern margin of the Kofu Basin and the older Cenozoicvolcanic rocks are distributed in the eastern part. The oldest Taragatoge Volcanic Rock consisting of subaqueous andesite effused at 7.9 Ma in the central part of the area. During 6.1-4.3 Ma, the Higashiyamanashi Volcano-Plutonic Complex was formed by eruption of rhyolite-dacite welded tuffs and minor andesite lava followed by intrusion of granodiorite in the eastern part. The Mizugamori Volcanic Rock of andesite composition occupied the central part derived from many vents, while the magnetic polarity changed from Gauss Normal Epoch to Matuyama Reversed Epoch in 2.4-1.7 Ma.
Kurofuji Volcano began its dacitic activity at 1.0 Ma forming the main shield of five pyroclas-tic-flow sheets and lava domes built up at the top at 0.5 Ma. The youngest andesite cone, the Kayagatake stratified cone, formed at the west flank of the main shield at 0.2 Ma.
These volcanic activities suggest that the volcanic front around this area moved about 20km from the east in 8-2 Ma to the west in 1.0-0.2 Ma, farther away from the Japan Trench.
