JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Oral

S (Solid Earth Sciences) » S-VC Volcanology

[S-VC50] [JJ] Volcanic and igneous activities, and these long-term forecasting

Sat. May 20, 2017 10:45 AM - 12:15 PM A04 (Tokyo Bay Makuhari Hall)

convener:Teruki Oikawa(Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Takeshi Hasegawa(Department of Earth Sciences, College of Science, Ibaraki University), Daisuke MIURA(Geosphere Sciences, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry), Nobuo Geshi(Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology), Chairperson:Akiko Matsumoto(Graduate School of Science, Hokkaido University)

11:30 AM - 11:45 AM

[SVC50-10] Omine volcano erupted just before Aso-4 pyroclastic flow

*Kousuke Shiihara1, Toshiaki Hasenaka1, ATSUSHI YASUDA2, Natsumi Hokanishi2, Yasushi Mori3 (1.Graduate School of Science and Technology, Kumamoto University, 2.Earthquake Research Institute, University of Tokyo, 3.Kitakyushu Museum of Natural History and Human History)

Keywords:Omine volcano, melt inclusion, honeycomb structure

Eruption of Omine pyroclastic cone and effusion of associated Takayubaru lava occurred just before the caldera-forming Aso-4 pyroclastic eruption. Composition of Takayubaru lava and that of Aso-4 pumice are similar, but the former was flowing eruption, while the latter was explosive volcanic eruption. We examined the composition of phenocrysts and melt inclusions in Omine scoria, and compared composition with those of Aso-4 pyroclastic flow deposits.
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.