文献一覧: 浜田盛久 (著者)

6 0 0 0 OA 鬼界カルデラ噴火の総合理解に向けた噴出物化学組成データベースの構築

著者: 上木賢太原口悟吉田健太桑谷立浜田盛久 Iona McINTOSH 宮崎隆羽生毅
出版者: 特定非営利活動法人日本火山学会
雑誌: 火山 (ISSN:04534360)
巻号頁・発行日: vol.68, no.1, pp.3-21, 2023-03-31 (Released:2023-03-31)
参考文献数: 60

Kikai caldera, a submarine caldera to the south of Kyushu, is the source of the youngest caldera-forming supereruption during the Holocene (i.e., the Kikai-Akahoya eruption at 7.3 ka). During its volcanic history, the Kikai caldera has experienced at least three caldera-forming supereruptions (i.e., the Kikai-Akahoya, Kikai-Tozurahara and Koabi eruptions). To better understand the processes of submarine caldera-forming supereruptions and the evolution of the large felsic magma bodies from which they derive, we have constructed a geochemical database for the eruption products of the Kikai Caldera, including proximal deposits and distal tephras (https://doi.org/10.6084/m9.figshare.20066630). We compiled geochemical data reported in various papers and proceedings from both domestic Japanese and international journals. The new database, comprising 413 individual samples from 59 publications, contains all available major- and trace-element concentrations, isotopic ratios, analytical methods, geographical coordinates (latitude, longitude, and altitude) of sampling points, age data, refractive index, and geological and petrological information. The database is freely available to the public online. Based on the constructed database, we review the current geochemical understanding of Kikai caldera magmatism and discuss geochemical characteristics of magmas from the Kikai caldera. The difference in magma composition between the two recent caldera-forming supereruptions (the Kikai-Akahoya eruption at 7.3 ka and the Kikai-Tozurahara eruption at 95 ka) is clearly seen in the compiled data. Moreover, we find that the distal tephra represents a more SiO2-rich magma composition than that of the proximal deposits, especially in the case of the Kikai-Akahoya eruption.

2023-06-28 06:04:22
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5 0 0 0 OA 島弧における初生マグマの含水量の推定:実験岩石学とメルト包有物分析からの制約

著者: 浜田盛久東宮昭彦
出版者: 一般社団法人日本鉱物科学会
雑誌: 岩石鉱物科学 (ISSN:1345630X)
巻号頁・発行日: vol.40, no.3, pp.91-100, 2011 (Released:2011-07-22)
参考文献数: 69

The slab-derived fluids and/or hydrous slab melts released from a subducted slab ascend into the mantle wedge, lower its melting temperature and thus induce generation of hydrous arc magmas. The estimation of H2O concentration in primary arc magmas provides an important constraint on pressure and temperature conditions of magma generation at subduction zones. This paper gives an overview of the estimation of H2O concentration in primary arc magmas by combining two petrological methods: experimental petrological studies and analyses of melt inclusions. Melting experiments of hydrous primary arc magmas have clarified that the P-T condition of magma generation shifts toward lower temperature and higher pressure with increasing H2O concentration. Another experimental constraint is that only primary magmas with low H2O (≤ 2 wt%) can erupt without modification of their primary composition by crystallization differentiation due to comparable dT/dP between olivine liquidus and basalt adiabat. However, this does not exclude presence of hidden H2O-rich primary magmas at depths. Indeed, the H2O concentrations in primary melt estimated from the analyses of primitive melt inclusions suggest wide variation (e.g., ~ 2 wt% at Kamchatka arc and ~ 4 wt% at Central American arc). H2O-rich primary magmas may ascend and erupt after differentiation and/or supply volatiles to magmas at shallower level and cause so-called “excess degassing”. Analyses of melt inclusions also clarified that the H2O concentration in primitive melt inclusions is almost constant or decrease from volcanic front to rear arc. This observation is opposite to a previous understanding that H2O concentration in primary melt increases as well as incompatible K2O across the arc.

2012-01-15 12:35:27
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1 0 0 0 IR 岩石学的にみた伊豆大島火山のマグマ供給系 (特集巨大地震と火山活動(Part 1))

著者: 浜田盛久
出版者: 東京大学地震研究所
雑誌: 東京大学地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)
巻号頁・発行日: vol.91, no.3, pp.41-54, 2016

Izu-Oshima is an active volcano located on the volcanic front of the Izu arc. It erupts island arc low-K tholeiite magma. During the past 150 years it has erupted repeatedly at intervals of 30-40 years. Thirty years have already passed since its last eruption (1986-1987) ; therefore, the next eruption is expected in the near future. The hypothesis that the next eruption of Izu-Oshima volcano is triggered by an aftereffect of the M9Tohoku-Oki earthquake, which took place on March 11th, 2011, is considered. In both the 9th century and the period between the 17th century and the 20th century, volcanism of Izu-Oshima volcano seems to have been activated in association with earthquakes occurring near the volcano. While some eruptions occurred after earthquakes, others occurred before earthquakes. It is possible that regional tectonic stress can trigger both major earthquakes and intense volcanic activity, although this hypothesis should be tested at Izu-Oshima volcano and/or elsewhere. Petrological studies of Izu-Oshima volcano are also reviewed to understand its magma plumbing system, providing useful information to prepare for its next eruption. It is proposed that polybaric crystallization differentiation of H2O-saturated magmas proceeds in both the magma chamber at 4 km depth (~3 wt.% H2O in melt) and the magma chamber at 9km depth (~5 wt.% H2O in melt). The H2O-rich nature of the basaltic magmas beneath the volcano suggests that a future eruption of Izu-Oshima volcano could be highly explosive if dissolved volatiles in melt are not sufficiently degassed from magma ascending through the conduit