K-Ar ages of high-magnesian andesite lavas from northern Kyushu, Japan

摘要

We determined the K-Ar ages for the high-magnesian andesites from Miocene-Pliocene period from Hikosan and Nagasaki areas in northern Kyushu, Japan. The obtained K-Ar ages of Hikosan and Nagasaki samples are 4.0-3.6 Ma and 5.8-3.7 Ma, respectively. These K-Ar ages suggest that the magmatisms of the high-magnesian andesites coincided with the development of the Okinawa Trough. The upwelling of the hot asthenospheric mantle associated with the backarc rifting probably has a close relationship with the origin of the northern-Kyushu high-magnesian andesite magma.