VOLCANIC ROCKS FROM KAYO-DAKE VOLCANO, AKITA PREFECTURE

Kayo-dake volcano is located in Akita Prefecture and is one of the volcanoes of Nasu Volcanic Zone. The main stage of volcanic activity was in the Early Quaternary. The volcano consists of lavas and a small amount of pyroclastic rocks. They are basalt, mafic andesite and andesite which belong to the tholeiite series and andesite of the calc-alkali rock, series. The rocks of the tholeiite series surpass those of the calc-alkali rock series in quantity. In the beginning of volcanic activity, basalt and mafic andesite of the tholeiite series were effused, and then, andesite belonging to the same rock series was erupted. After an intermission of activity, andesite of the calc-alkali rock series forming parasitic volcanoes, lava flows from a central crater, and a central cone, was effused. It may be a distinctive feature of this volcano that a comparatively large amount of andesite of the tholeiite series is present.