著者

北風 嵐

出版者

日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.39, no.3, pp.104-109, 2010-05-30

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Sulfide blebs composing of bornite solid-solution, mooihoekite, isocubanite and pyrrhotite occur in andesite from the lava dome, Tarumai volcano, Hokkaido, Japan. The lava dome consists of two-pyroxene andesite. Some bornite solid-solutions are found as exsolution lamellae in mooihoekite which is originally crystallized as intermediate solid-solution (iss) in the Cu-Fe-S system at high-temperature, included in magnetite phenocrysts of the andesite. Isocubanite occurs closely associating with pyrrhotite included in orthopyroxene phenocrysts of the andesite, and is exsolved from the Cu-bearing pyrrhotite. Some bornite solid-solutions and mooihoekite are found in a ground mass as micro-crystals. The magnetite including mooihoekite and bornite solid-solution, and the orthopyroxene including pyrrhotite and isocubanite may be crystallized at different conditions. The crystallization temperatures are about 950 °C for the silicate melt including magnetite phenocrysts, and about 1150 °C for the orthopyroxene bearing silicate melt. Therefore, this andesite magma is thought to be formed by the magma mixing.<br>