K-Ar age of high magnesium andesite dikes at the Toki River in Gifu Prefecture, central Japan.

Abstract

A high-magnesium andesite dike swarm intruding into the Jurassic mélange of the Mino-Tamba Belt and the Cretaceous Toki Granite is exposed along the Toki River in central Japan. At the time of intrusion, the direction of the maximum horizontal compressive stress was E-W in this area, as indicated by the predominant direction of the dike swarm. New K-Ar age dating suggests that the intrusive age of the dike swarm is 60-70 Ma. We point out of possibility that high-magnesium andesite magmatism occurred at 60-70 Ma in the eastern part of Inner Zone of Southwest Japan.