5:15 PM - 6:30 PM
[SVC48-P12] Chemical composition of Omine volcanic products which actived before Aso-4 pyroclastic flow
Keywords:Omine volcano, Takayubaru lava flow, Omine scoria, Melt inclusion
Eruption of Omine pyroclastic cone and effusion of associated Takayubaru lava occurred just before the caldera-forming Aso-4 pyroclastic eruption. Composition of Omine scoria and that of Takayubaru lava are similar, but the former shows a wider variation and a little more felsic than the latter.
Whole-rock chemical composition of Takayubaru lavas overlaps with that of Aso-4 pyroclastic flow deposits in some elements, however they show distinct compositional trends in other elements such as TiO2 and Na2O.
We further examined the composition of melt inclusions in the phenocrysts of plagioclase and orthopyroxene in Omine scoria by FT-IR. Composition of Omine melt inclusions in plagioclase is plotted in a narrow range of 67-70 SiO2, contrasting with 71-74 wt.% SiO2 of Aso-4 pyroclastics. Omine melt inclusions show distinct trends in MgO, FeO, TiO2 vs. SiO2 plots, and have more SO3 and less H2O than Aso-4 pyroclastics. Melt inclusions in plagioclase are SiO2-poor and less fractionated than groundmass glass. Thus they probably represent earlier stage of magma supply system.
The plagioclase phenocryst composition of Omine scoria shows a unimodal distribution. Whereas, those of Aso-4 pyroclastic flow deposits often show bimodal distribution and are more Ab-rich. Plagioclase phenocrysts of Omine scoria are either clear or with honeycomb structure. They both are in the similar compositional range; the latter showing a little wider range.
All the results indicate that the magma supply system of Omine volcano was different from that of Aso-4.
Whole-rock chemical composition of Takayubaru lavas overlaps with that of Aso-4 pyroclastic flow deposits in some elements, however they show distinct compositional trends in other elements such as TiO2 and Na2O.
We further examined the composition of melt inclusions in the phenocrysts of plagioclase and orthopyroxene in Omine scoria by FT-IR. Composition of Omine melt inclusions in plagioclase is plotted in a narrow range of 67-70 SiO2, contrasting with 71-74 wt.% SiO2 of Aso-4 pyroclastics. Omine melt inclusions show distinct trends in MgO, FeO, TiO2 vs. SiO2 plots, and have more SO3 and less H2O than Aso-4 pyroclastics. Melt inclusions in plagioclase are SiO2-poor and less fractionated than groundmass glass. Thus they probably represent earlier stage of magma supply system.
The plagioclase phenocryst composition of Omine scoria shows a unimodal distribution. Whereas, those of Aso-4 pyroclastic flow deposits often show bimodal distribution and are more Ab-rich. Plagioclase phenocrysts of Omine scoria are either clear or with honeycomb structure. They both are in the similar compositional range; the latter showing a little wider range.
All the results indicate that the magma supply system of Omine volcano was different from that of Aso-4.