Petrological Study of the Myoko and Kurohime Volcanoes, Japan: Crystallization Sequence and Evidence for Magma Mixing

Abstract

Quaternary volcanic rocks of the Myoko and Kurohime volcanoes, central Japan, are divided into two types, R-type and N-type, according to the presence or absence of reversely zoned mafic phenocrysts. Disequilibrium phenocryst assemblages, such as Mg-rich olivine with Fe-rich orthopyroxene and augite, Mg-rich normally zoned pyroxenes with Fe-rich reversely zoned ones, and a wide (commonly bimodal) compositional variation of plagioclase phenocrysts are commonly observed in the R-type rocks.