11:30 AM - 11:45 AM
[SVC50-10] Omine volcano erupted just before Aso-4 pyroclastic flow
Keywords:Omine volcano, melt inclusion, honeycomb structure
Phenocrysts of Omine scoria is composed of plagioclase, clinopyroxene, orthopyroxene and opaque minerals, and scoria contain microphenocrysts of hornblende. Most of Plagioclase has honeycomb structure.
Whole-rock chemical composition of Takayubaru lava and that of Omine scoria are similar. Whole-rock chemical composition of Omine scoria overlap with that Aso-4 pyroclastic flow deposits in some elements, however they show distinct compositional trends in other elements such as TiO2, Na2O and MgO.
The plagioclase phenocryst composition of Omine scoria shows bimodal distribution. Main peak is An55 and sub peak is An45. Plagioclase which has sub peak has honeycomb structure and show reverse zoning. The clinopyroxene phenocryst composition shows unimodal distribution and normal zoning, but the orthopyroxene phenocryst composition shows normal and reverse zoning.
Composition of Omine melt inclusion in plagioclase, clinopyroxene and orthopyroxene are plotted in a narrow range of 68 - 70 wt.% SiO2, but several melt inclusion in orthopyroxene are plotted 71 – 74 wt.%. Omine melt inclusions show distinct trends in major element vs. SiO2 plots, and have less H2O than Aso-4 melt inclusion.
Sr isotopic ratios of Aso-4 and Takayubaru lava are nearly equal. The results indicate that the magma supply system of Omine volcano was different from that of Aso-4. In addition, Omine magma chamber was injected magma of different composition.