| Timetable |
| Download Conference Program |
| Download All Abstracts |
| Zoom Access |
| Corporate Program |
Poster Presentations
Day 3, June 24（Tue.）
Room P (Maesato East, Foyer, Ocean Wing)
- 3P-AM-47
Helium Isotopes in Olivine and Pyroxene Crystals in Volcanic Rocks Revealing the Magma Plumbing System of the Kirishima Volcano Group
(1School of Science, UTokyo, 2RCAST, UTokyo, 3ERI, UTokyo, 4Kumamoto Univ., 5Nippon Koei)
oRai Yoneda1, Hirochika Sumino2, Masataka Kawaguchi3, Toshiaki Hasenaka4, Yasuhisa Tajima5, Nanae Fukushima2
Noble gases, particularly helium isotopes, are valuable for tracing Earth's materials and volcanic activity. The 3He/4He ratio varies across geochemical reservoirs: 1.4×10-6 (= 1 RA) in the atmosphere, high in the mantle (~8 RA), low in the crust (<0.02 RA). Helium isotopes in volcanic gases can indicate eruptions but are limited because of high diffusivity and atmospheric and crustal interactions. To address this, noble gas isotopes in olivine and pyroxene crystals were analyzed. These minerals trap magma inclusions, preserving helium isotopic signatures. In this study, minerals that erupted in the Kirishima volcano group, which includes the Shinmoe-dake and Ohachi volcanoes, were analyzed. Noble gases were released by crushing the minerals in a vacuum, purified with hot Ti-Zr getters, and separated by an activated charcoal trap. Then their isotopic compositions were measured by a magnetic sector mass spectrometer. The result showed that pyroxenes had more mantle-like 3He/4He ratios (~8 RA) than olivines (~7.4 RA) for the samples from Shinmoe-dake, suggesting differences in crystallization timing and magma degassing. Ohachi lavas showed even higher 3He/4He (7.9–8.4 RA), implying a deeper magma source than Shinmoe-dake.