Bull. Volcanol. Soc. Japan
Vol. 58 (2013) No. 1, pp. 19-42

ArticleTemporal Variation for Magmatic Chemistry of the Sakurajima Volcanoand Aira Caldera Region, Southern Kyushu, Southwest Japan since 61 kaand Its Implications for the Evolution of Magma Chamber System
Masaki TAKAHASHI＊, Tadashi OTSUKA＊＊, Hisashi SAKO＊＊, Hiroshi KAWAMATA＊＊＊,Maya YASUI＊, Tatsuo KANAMARU＊, Mei OTSUKI＊＊＊＊, Tetsuo KOBAYASHI＊＊＊＊＊,
Kazuhiro ISHIHARA＊＊＊＊＊＊ and Daisuke MIKI＊＊＊＊＊＊(Received October 5, 2011 ; Accepted December 19, 2012)
The temporal variation of magmatic chemistry and the evolution of magma chamber system of the Sakurajima
volcano and Aira caldera region since 61 ka are studied based on the whole-rock major element, incompatible traceelement and rare earth element chemistry of the eruptive products. The magmas of the Sakurajima volcano and Airacaldera region since 61 ka consist of four groups: (1) basaltic to basaltic andesitic magma of the mantle origin, (2)rhyolitic to high silica rhyolitic magma of the crustal origin, (3) dacitic magma and (4) andesitic magma produced bymagma mixing of the mafic magma of mantle origin and the crustal felsic magma. Around 61 to 60 ka, basaltic tobasaltic andesitic, andesitic and rhyolitic magmas were active in the Aira caldera region, and the Shikine andesite andthe Iwato pyroclastic flow deposit were erupted. After a dormant period of about twenty-four thousands of years, therhyolitic magmatism resumed and the voluminous high silica rhyolitic magma erupted at 29 ka to form the large-scale
Osumi pumice fall and Ito pyroclastic flow deposits. The felsic magma produced the Iwato pyroclastic flow deposit
and the Osumi pumice fall and Ito pyroclastic flow deposits were similar in composition; the latter high silica rhyolite
can be derived from the former rhyolite by crystallization differentiation. The rhyolitic to high silica rhyolitic magma
chamber system was stable and long-lived with duration of about thirty thousands of years. The magmatic activity of
the Sakurajima volcano began at 26 ka after a quiescent period of about three thousands of years. The Moeshimarhyolitic magma discharged at 13.8 ka in the Aira caldera constitute another magma chamber system different from thatof the Sakurajima volcano. The magma chamber system of the Sakurajima volcano was composed of the low Ti-P typeand high Ti-P type dacitic and andesitic magmas. The magma chamber system of the low Ti-P type, which was activefrom about 14 to 4 ka, comprises at least the three sub-systems based on the whole-rock chemistry, while that of thethhistorical eruption since 8 C is restricted to the high Ti-P type and consists of the three sub-systems, the youngest ofwhich has been active since the subaqueous An-ei eruption at 1779AD. The duration of the activity of each magma
chamber sub-system of the Sakurajima volcano is rather short, the time span of which is thousands to several hundredsof years.
Key words : Sakurajima volcano, Aira caldera, felsic magma, magmatic chemistry, magma chamber

1．Introduction
The Sakurajima volcano in southern Kyushu is one of
the representative active dacitic to andesitic volcanoes in
the late Quaternary Japanese islands, which is constructedon the southern margin of the large-scale Aira caldera with＊

Department of Geosystem Sciences, College of Humanitiesand Sciences, Nihon University, 3-25-40 Sakurajyosui
Setagayaku, Tokyo 156-8550, Japan.
＊＊
Graduate School of Science and Technology, Ibaraki
University, 2-1-1 Bunkyo, Mito 310-8512, Japan.
＊＊＊
Department of Earth Sciences, Faculty of Science, Ibaraki
University, 2-1-1 Bunkyo, Mito 310-8512, Japan.
＊＊＊＊
Graduate School of Integrated Basic Sciences, Nihon University, 3-25-40 Sakurajyosui Setagayaku, Tokyo 1568550, Japan.

a dimension of 24×20 km. The eruption of the Sakurajima volcano is now continuing from the Showa crater atthe upper slope of the eastern flank of the volcano. Themagma of the Sakurajima volcano is estimated to be being
fed from the magma chamber beneath the Aira caldera, to＊＊＊＊＊

Graduate School of Science and Technology, Kagoshima
University, 1-21-35 Korimoto, Kagoshima 890-0055,Japan.
＊＊＊＊＊＊
Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, SakurajimaYokoyamacho, Kagoshima 891-1419, Japan.
Corresponding author: Masaki Takahashi
e-mail: takahashi.masaki@nihon-u.ac.jp