Variation of petrological features caused by style of eruption in the western volcanic chain of the Aonoyama Volcano Group, Southwestern Japan

Abstract

Abu Monogenetic Volcano Group and Aonoyama Volcano Group, which are active in the Quaternary, are distributed in the northern part of Yamaguchi Prefecture. The Abu Monogenetic Volcano Group are composed of more than 50 volcanoes with diverse topography, such as pyroclastic cones, lava plateaus, and lava dome with flat tops. This magma was produced by melting the lithosphere due to the rise of the mantle asthenosphere. On the other hand, the Aonoyama Volcano Group is a Quaternary island arc volcano related to the subduction of the Philippine Sea Plate and consists of more than 20 lava domes. Both the Abu Monogenetic Volcano Group and the Aonoyama Volcano Group are aggregates of small volcanic bodies. There are significant differences between these groups in topographical features and magma origin in spite of neighboring position of them. Recent studies for Aonoyama Volcano Group have reported that Nabeyama shows a different topography from the lava dome, and that Chojagahara represents a lava plateau. Because the Aonoyama Volcano Group has not only lava domes but also various topography, it is necessary to review the definition of the Aonoyama Volcano Group. This study aims to clarify the style of eruption of the western volcanic chain of the Aonoyama Volcano Group, which remains volcanic topography well, based on geology and petrography and to consider the variation of petrological features caused by these styles.