ABSTRACT

Thirteen dike swarms in Northeast Japan were dated by the K-Ar method. The K-Ar ages in this study give some crucial constraints to the volcanostratigraphy and imply that the geological situation of some dike swarms estimated in the other studies should be reexaminned while other dike swarms showed the K-Ar ages concordant with the geological ages. Available K-Ar ages of the volcanic rocks from the present and other studies indicate that the volcanic front in Northeast Japan had a temporal position about 22–23 Ma ago to the east of that in the Quaternary and that the volcanism appears to have been inactive from 17 to 21 Ma ago.