抄録
We investigated the geology of Okanodake volcano and the area adjacent to it in the Futago Volcanic Group, NE Kyushu, Japan. Based on the geology and petrology of this area, the formation of Okanodake Volcano (biotitehornblende dacite) began with phreatomagmatic eruptions and ceased with effusion of lava. The age of the eruption is assumed to be 1.19Ma. The volcanic products consist of pyroclastic deposits, pyroclastic surge deposits and block-and-ash flow deposits, and intrusive rock. SiO2 contents range from 63-67wt.% and K2O contents range from 1.9-2.4wt.%. Each of the volcanic products is classified within the calc-alkali series. The volume of the various volcanic products were calculated to be ca. 0.07km3, 0.008km3, and 0.002km3, respectively. The total volume is ca. 0.06 DRE km3.
