Japan Geoscience Union Meeting 2016

Presentation information


Symbol S (Solid Earth Sciences) » S-VC Volcanology

[S-VC48] Volcanic and igneous activities, and these long-term forecasting

Sun. May 22, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

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), Yoshihiro Ishizuka(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Nobuo Geshi(Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology)

5:15 PM - 6:30 PM

[SVC48-P12] Chemical composition of Omine volcanic products which actived 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, 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.