1993 Volume 88 Issue 7 Pages 352-358
The Miocene Tomari volcanic rocks occurring in the Shimokita Peninsula, Northeast Japan arc were dated by K-Ar method. The results show that all the Tomari volcanic rocks have almost similar K-Ar ages of about 13-15 Ma, although they were stratigraphically divided into five units. This indicates that all these volcanic units in the Tomari area were formed by a nearly simultaneous volcanism of Middle Miocene age along the northern-most portion of the volcanic front of 13-16 Ma, which lie 30-50km east of the Quaternary volcanic front.