ABSTRACT

Ca, Sr and Ba contents of various volcanic rocks from four volcanoes (Okata, Gyojanoiwaya, Fudeshima and Oshima) in Oshima, Izu Islands, Japan, have been determined by an inductively coupled plasmaoptical emission spectrometry. In a Sr/Ca-Ba/Ca diagram, three older volcanoes (Okata, Gyojanoiwaya and Fudeshima) gave the same Sr/Ca-Ba/Ca systematics, while younger volcano (Oshima) showed a different Sr/Ca-Ba/Ca systematics. The two different systematics seem to have branched off from a common precursor, suggesting that the primary magma was the same in terms of degree of partial melting of “mantle materials”, but crystal fractionation process in “magma chamber” was different.