K-Ar AGE DETERMINATIN OF VOLCANIC ROCKS FROM THE HOHI GEOTHERMAL AREA, KYUSHU, JAPAN.

Seventeen volcanic rocks of Pliocene to Pleistocene ages from the Hohi geothermal area were dated by K-Ar method. Ages of about 0. 4-3. 1 Ma were obtained more precisely than before. Obtained age data are shown in connection with a previous stratigraphic classification: 'Kusu Group and its correlatives'; 0. 6-3. 1 Ma, //Hohi volcanics and its correlatives'; 0. 8-2. 0 Ma, 'Bungo Volcanics'; 0. 4-1. 1 Ma. , and 'Early Younger Volcanics': 0. 4-0. 7 Ma. Above results suggest that previous classification on the basis of the lithologic similarities does not represent time-stratigraphic relations of the volcanic rocks in the Hohi geothermal area. In order to evaluate previous K-Ar age data in the Hohi geothermal area, some volcanic rocks either from the same outcrops or from the same strata as those of the previous age data were analyzed. Both sets of data are concordant when considering the analytical error, and previous K-Ar data were found to be reliable.