Permalink : http://hdl.handle.net/2115/36671

Olivine tholeiite (transitional type between alkaline and tholeiitic basalt), quartz tholeiite and calc-alkaline andesite suite of Pliocene age are widely distributed in the central part of Tottori Prefecture, west Japan. Pyroxenes in this volcanic suite were analysed with the electron microprobe. From olivine tholeiite to quartz tholeiite, Ca-rich clinopyroxenes become rich in Fe and poor in Ca with progressive crystallization. Ca-rich clinopyroxenes in the andesites are similar to, or higher in Mg and Ca contents than those in the basalts. Ca-poor pyroxenes in the andesites have higher 100Mg/(Mg+Fe+Mn) ratios than those in the basalts. These features are considered to be characteristic in the calc-alkaline volcanic suite and probably reflect constant oxygen fugacity during the crystallization of the pyroxenes.