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Poster Presentations
Day 2, June 23（Mon.）
Room P (Maesato East, Foyer, Ocean Wing)
- 2P-AM-31
Noble gas isotope analyses of the volcanic rocks in Ioto island (Iwo-Jima) from the latest eruptions since 2022
(1Univ. Tokyo, Komaba, 2Univ. Tokyo, RCAST, 3NIED)
oSoho Yamamoto1, Hirochika Sumino2, Masashi Nagai3
Ioto Island (Iwo-Jima) is one of the active volcanic islands of the Izu-Bonin-Mariana island arc, located about 1,250 km south of Tokyo. In July 2022, a magmatic eruption spewing pumice (foamed volcanic rock) occurred off the coast of Okinahama in the southern part of Ioto for the first time in recorded history. One main purpose of this study is to compare the helium isotopic ratio between the volcanic rock and the volcanic gas in Ioto and to reveal the interaction between them. Olivine and pyroxene were collected from the pumice and noble gas isotopes were measured with a magnetic sector mass spectrometer (modified VG-5400) at the University of Tokyo. 3He/4He of olivines, pyroxenes were 3.3 - 4.7, 2.0 - 4.5 Ra (where atmospheric 3He/4He of 1.4×10-6 ≡ 1 Ra), respectively. This value is lower than the volcanic gas values collected in 1997-2002, ranging from 4.7 to 5.6 Ra (Sumino et al., 2004) and also lower than the highest value of the volcanic gases (2024) of 6.0 Ra. This indicates that minerals of the pumice may have trapped low 3He/4He magma in the shallow magma chamber where crustal contamination occurs.