抄録
We investigated U-series disequilibria of volcanic eruptives over the past 500 years from the Miyakejima volcano, Izu arc, Japan. The Miyakejima eruptives show 1) a trend almost parallel to the equiline in a (230Th/232Th)-(238U/232Th) diagram, and 2) a positive linear correlation in a (226Ra/230Th)-1/Th diagram. This is explained by the injection of a basaltic magma, followed by the change of the magma composition from basaltic to andesitic by mineral crystallization and wall-rock assimilation. Chemical diversity of the andesitic magma has originated from the different degree of crystallinity in the magma chamber, presumably due to the heterogeneity of magma temperature.
