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Day 2, June 11（Tue.） Room P1 (Multipurpose Hall)・Room P2 (Conference Room 101+102)
- 2P-22（1A-O1-1515）
Insights into the Magma Plumbing System of the Kirishima Volcano Group from Isotopic Ratio of Helium in Olivine
(1Univ. Tokyo, 2Kumamoto Univ., 3Nippon Koei Co.)
oRai Yoneda1, Hirochika Sumino1, Masataka Kawaguchi1, Toshiaki Hasenaka2, Yasuhisa Tajima3
Here, we report isotopic compositions of noble gases in olivine in pumice of the Shinmoe-dake 2011 eruption. Geophysical observations and petrological investigations on the Kirishima volcano group, including Shinmoe-dake, have suggested that there are deep basaltic and shallow silicic magma chambers) (Suzuki et al., 2013; Aizawa et al., 2014). In addition, data on noble gas isotopes in the fumaroles have been accumulated including nearby volcanoes (Sumino, et al., 2020). This study aimed to discuss the consistency between the proposed subsurface structure and the isotopic compositions of noble gases through a comparison of the isotopic ratios of noble gases in the phenocrysts and fumaroles. The isotopic ratios of helium resulted in 3He/4He = 7.46 ± 0.09 RA (1 RA = 1.4×10-6). This is lower than that of Iwo-yama (~7.9 RA) (Sumino, et al., 2020). Both the Iwo-yama and Shinmoe-dake magmas are thought to be derived from the silicic magma chamber fed by the deeper basaltic magma chamber (Aizawa et al., 2014). This suggests that a gas flow pathway directly connects the deeper magma chamber and the Iwo-yama fumaroles or that the crustal assimilation process of the magma ascending during the eruption was recorded in the olivine phenocrysts.