K-Ar ages of the Izu-Bonin Islands

Abstract

Several volcanic rocks from O-shima, Kozu-shima and Hachijo-jima of the Izu Islands, from Chichi-jima and Haha-jima of the Bonin Islands and from Iwo-jima of the Iwo Islands were dated by K-Ar method. The rocks from the Izu Islands give the ages of less than 2— 3m.y., while the ages of the rocks from Chichi-jima and Haha-jima are about 30—40m.y. The rock from Iwo-jima indicates a very young K-Ar age of about 0.03 m.y. These results confirm that there is a clear difference in age of volcanic activity between the Izu Islands and the Bonin Islands. This difference has also been suggested geologically. © 1970, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.