Magma mixing and degassing processes of 2011 eruption series of Kirishima volcano, Japan, based on chemical analyses of minerals and melt inclusions
Abstract
Petrological studies of the essential products of phreato-magmatic, sub-Plinian, Vulcanian and minor ash eruptions in 2011 eruption series of Shinmoedake, Kirishima volcanic group, Japan, were carried out. Using the combined geological, petrological and gas emission observations from the 2011 eruptions, I investigated magma ascent and degassing processes of the eruptions. The bimodal plagioclase core composition, relatively small rims of olivines and pyroxenes, and diffusion profiles of the olivines indicate the mixing of mafic magma and felsic magma in several days before the sub-Plinian eruption. Melt inclusion analysis indicated that the end members of the magma mixing were basaltic andesite and dacite magmas and its mixing ratio was estimated to be 0.4 of the basaltic andesite. Magmas of the following Vulcanian and ash eruptions in February to June have similar mode composition, chemical compositions of phenocrysts, groundmass minerals and groundmass and zoning profiles of olivines of the eruptive products of to those of the sub-Plinian eruptions. These results indicate that magma mixing process proposed for the sub-Plinian eruptions also occurred in eruptions showing various styles. These results suggest that the mafic magma input to felsic magma intermittently occurred after the sub-Plinian eruptions to cause the minor eruptions in March to June. The amount of the degassed magma that was estimated based on sulfur content of melt inclusions of the end member magmas and SO2 flux observation was larger than that of eruptive products in 2011, indicating the degassing of the magma in the chamber due to convection of the magma in a conduit.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.V53B2830S
- Keywords:
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- 1043 GEOCHEMISTRY / Fluid and melt inclusion geochemistry;
- 8410 VOLCANOLOGY / Geochemical modeling;
- 8430 VOLCANOLOGY / Volcanic gases;
- 8434 VOLCANOLOGY / Magma migration and fragmentation