[SVC36-P09] Outgassing and Oxidation processes of viscous magmas inferred from micro-Raman and IR spectroscopy
Keywords:Oxidation texture, Raman spectroscopy, IR spectroscopy, obsidian
At the Akaishiyama obsidian lava on Shirataki, northern Hokkaido, Japan, we can observe the red-colored oxidized obsidian mingled with black-colored obsidian. The mingled obsidian shows various contrasts and distributions on the hand specimen, and we can consider that such various oxidation texture reflects the different mechanisms of outgassing and oxidation during the eruption. In this study, we used the microRaman and IR spectroscopy to characterize the oxidation state in the obsidian. We obtained the 2 types of Raman spectra of oxide microlites in red and black obsidians, respectively. Compared with referential spectra, we identified the captured spectrum as magnetite and hematite. Furthermore, the height of 470 cm-1 on the glassy part shows the degrees of oxidation. The IR spectroscopy shows the different water concentration between red-colored and black-colored obsidian glasses. The red-colored oxidized glass shows lower water concentration than black-colored obsidian glasses. Based on the analytical results of microRaman and IR spectroscopy and, we discuss the formation process of heterogeneous oxidation textures during the eruption.