本州弧・琉球弧会合部における火山活動

抄録

The late Cenozoic crustal movements of Japanese islands are represented by the Green tuff and Island-arc movements (FuzITA, 1970). Kyushu is one of the most important regions of the late Cenozoic volcanism in southwest Japan, because it occupies the position of geologic joint between the Honshu (Japan proper) and Ryukyu arcs, which are characterized by many different volcanic activities. The volcanic activities of the Green tuff movement in Kyushu, which began in the early Miocene and terminated in the late Pliocene. These volcanism are represented by Green tuff, the Hizen dolerites, the Sobosan and first Setouchi volcanics, the Matsura basalts and other volcanics of the Tairiku (Continental) series. The volcanic activities of the Island-arc movement in Kyushu, which began in the early Pleistocene period. These volcanism are represented by the Hohi and Bungo volcanic activities, and the activities of volcanoes of the Sanin and Ryukyu series. The Hohi and Sanin volcanic activities are closely related the Honshu and Ryukyu arcs. The pyroclastics and lavas of the Hohi volcanic rocks in the early Pleistocene are widely distributed in northern and central Kyushu, which is located geologic joint between the Honshu and Ryukyu arcs. Moreover, it is conceivable that the early Pleistocene period was the immature stages of the recent island arc, and at the same time the recent trench had just constituted in this period. Distribution of the volcanoes of the Sanin volcanic series in the middle and late Pleistocene was controlled by geologic structure of two arcs, which is combination of ENE-WSW direction of the Honshu arc and NNE-SSW direction of the Ryukyu arc.