K-Ar ages of the Hiruzen Volcano Group and the Daisen Volcano ( Japan).

Abstract

Seventeen volcanic rocks of the Hiruzen Volcano Group and the Daisen Volcano, in SW Japan, were dated by the K-Ar method to clarify the age of volcanic activity in this region and the evolution of these composite volcanoes. The eruption ages of the Hiruzen Volcano Group were revealed to be about 0.9 Ma to 0.5 Ma, those of the Daisen Volcano to be about 1 Ma to very recent. These results are consistent with geological and plaeomagnetic data of previous workers. Effusion of lavas in the area was especially vigorous at 0.5+ or -0.1 Ma. The aphyric andesite, whose eruption age had been correlated to Wakurayama andesite (6.34+ or -0.19 Ma) in Matsue City and thought to be the basement of the Daisen Volcano, was dated to be 0.46+ or -0.04 Ma. It indicates that petrographically similar aphyric andesite erupted sporadically at different time and space in the San'in district.-from English summary