K-Ar age of the volcanic rocks, the sedimentation and the deformation in the Omine Belt, Northern Fossa Magna, central Japan.

Abstract

K-Ar ages for four volcanic units were measured in the Omine Belt, Northern Fossa Magna, central Japan. Two samples of ash flow tuffs for the measurement were taken from the lower Miasa Formation, one sample of a lava from the middle Taroyama Andesite and one of an ash flow tuff from the upper Omine Formation. The K-Ar ages all resulted around 2 Ma. It means that the Omine Belt which built up more than 3,000m thick fans formed in relatively short time span in a pullapart basin around 2 Ma.