Japan Geoscience Union Meeting 2014

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

[S-VC53_28PO1] volcanic activities and tectonics

Mon. Apr 28, 2014 6:15 PM - 7:30 PM Poster (3F)

Convener:*Geshi Nobuo(Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology), Takuya NISHIMURA(Disaster Prevention Research Institute, Kyoto University), Ryuta FURUKAWA Ryuta(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Daisuke MIURA(Geosphere Sciences, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry), Takeshi Hasegawa(Department of Earth Sciences, College of Science, Ibaraki University), Kiyoshi Toshida(Geosphere Science Sector, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry)

6:15 PM - 7:30 PM

[SVC53-P03] Correlation between petrology and magneto-stratigrapphy of Holocene volcanic products from Aso central cones

*Yuichiro HIRAKAWA1, Toshiaki HASENAKA1, Nobutatsu MOCHIZUKI2, Yasushi MORI3 (1.Grad School Sci & Tech, Kumamoto Univ., 2.Priority Organization for Innovation and Excellence, Kumamoto University, 3.Kitakyushu Museum of Natural History and Human History)

Keywords:post-caldera central cones of Aso volcano, volcanic products, Holocene, paleomagnetic directions, petrography, chemical compositions

We collected samples from 25 sites where Yato et al. (2013) and Miyabuchi et al. (2012) reported magneto-stratigraphy of six different lava flows distributed in the northwestern region of Aso central cones. We conducted petrographic descriptions and chemical analyses of these samples and correlated them with paleomagnetic directions and stratigraphy of Miyabuchi (2009) based on radiocarbon dating.Kijimadake lava is divided into two lava flow units with different paleomagnetic directions suggesting interval of at least several hundreds of years. They show the same mineral assemblage, but different groundmass texture, modal composition and whole-rock chemical composition. The upper lava flow unit has the same petrological characteristics as Kishimadake scoria, whose estimation age was 4000 y.b.p. from the radiocarbon dating.Possibility of multiple eruptions has been suggested for Ojodake lava flows, because they are intercalated by soil, and show different paleomagnetic directions. However, no distinction was made in petrographic descriptions and chemical compositions between these lava flows. Six different lava flows younger than Akahoya tephra have similar appearance and similar petrographic characteristics, however they are distinguishable by chemical compositions. Lava flow units with possible simultaneous eruptions (e.g. old Kijimadake lava and Nakadake younger stage lava, Kamikomezuka scoria and old Ojodake lava) show about 1% difference in SiO2 content. A series of Holocene lava flows in Aso central cones are possibly derived from a common magma supply system with different conduits.