K-Ar dating of the volcanic rocks in the Ryukyu arc

Abstract

High magnesian andesites from Kume-jima and Iriomote-jima, the Ryukyu islands were dated by the K-Ar method with the basalts from Kobi-sho and Sekibi-sho, the Senkaku islands. The obtained K-Ar ages of the high magnesian andesites are 6.08 ± 0.46 Ma and 13.1 ± 1.1 Ma for the sample (s) from Kume-jima and Iriomote-jima, respectively. The volcanic activity of the high magnesian andesite magma continued intermittently for at least 6 Ma. The K-Ar age of the basalt from Sekibi-sho is 2.59 ± 0.19 Ma. The age of the basalt lava from Kobi-sho is as young as 0.2 Ma or even younger, and indicates that Kobi-sho is a Quaternary volcano.