著者

佐野 貴司 石川 晃 清水 健二 Tejada Maria・L・G 羽生 毅 中西 正男 石塚 治

出版者

独立行政法人国立科学博物館

雑誌

基盤研究(A)

巻号頁・発行日

2018-04-01

著者

佐野 貴司 テハダ マリア ルイサ 中西 正男 羽生 毅 三浦 誠一 末次 大輔 利根川 貴志 石川 晃 清水 健二 淸水 祥伽

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.130, no.4, pp.559-584, 2021-08-25 (Released:2021-09-23)

参考文献数

163

被引用文献数

2 4

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Large Igneous Provinces (LIPs), such as the Ontong Java Plateau (OJP) in the western equatorial Pacific, provide information on mantle processes and composition, and their formation may have global environmental consequences. The OJP is the largest oceanic plateau and is probably the most voluminous igneous edifice on Earth. Despite its importance, the size, volume, and formation rate of the OJP are not yet well constrained. The maximum extent of OJP-related volcanism may be even greater than currently estimated, because volcanological studies indicate that long lava flows (or sills) from the OJP may have reached the adjacent Nauru, East Mariana, and possibly Pigafetta basins. Moreover, the similarity in age and some geochemistry of lavas from the Ontong Java, Hikurangi, and Manihiki plateaus suggests that they once may have been part of a single LIP (Ontong Java Nui, OJN). If true, the massive volcanism may have covered > 1% of the Earth's surface. The lack of detailed knowledge of the size, age, and composition of the OJP has given rise to various models, such as a surfacing mantle plume head, bolide impact, and fusible mantle melting, but no model satisfies all observational data and no consensus has been reached on its origin. The OJP is divided into the High Plateau to the west and the Eastern Salient to the east. The basaltic basement of the OJP was cored at seven sites during Deep Sea Drilling Project (DSDP Site 289) and Ocean Drilling Program (ODP Sites 289, 803, 807, 1183, 1185, 1186, and 1187) expeditions, but all sites are exclusively located on the High Plateau. In order to examine the true extent of the OJP (i.e., whether the flows in the Nauru, East Mariana, and Pigafetta basins, as well as the Manihiki and Hikurangi plateaus are parts of the OJN), we propose drilling in the Eastern Salient and adjacent basins to recover basement samples. We also propose drilling through the sedimentary section on the Magellan Rise, a small plateau that formed > 20 Myr before the proposed OJN emplacement. Because of its greater age, the sedimentary sequence on the Magellan Rise may preserve ash layers or other chemical tracers that cover the entire eruptive history of OJN. The sediment layers from the Magellan Rise are also useful for evaluating environmental effects of OJN emplacement, including older and younger perturbations related to other LIPs.

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

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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.

著者

兼岡 一郎 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.38, no.4, pp.145-150, 1993

著者

清杉 孝司 巽 好幸 鈴木 桂子 金子 克哉 中岡 礼奈 山本 由弦 羽生 毅 清水 賢 島 伸和 松野 哲男 菊池 瞭平 山口 寛登

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-03-13

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Catastrophic caldera-forming eruptions that discharge more than 40 km3 of Si–rich magma as pyroclastics are rare but extremely hazardous events (eruption magnitude >7). Estimating the eruption volume of pyroclastics and the magma discharge rate in caldera–cycle is essential in evaluating the risk and cause of catastrophic caldera–forming eruptions. For this reason, we took sediment cores with Hydraulic Piston Coring System (HPCS) and Short HPCS (S-HPCS) of D/V Chikyu at Kikai volcano in January 11–14, 2020. Kikai volcano (Kikai caldera) is located about 45 km off southern Kyushu Island, Japan. Except two islands (Satsuma Iwo-Jima Island and Take-Shima Island) on the northern part of the caldera rim, most of the caldera structure is under the sea. At Kikai volcano, three ignimbrites are known; the 140 ka Koabi ignimbrite, the 95 ka Nagase ignimbrite, and the latest 7.3 ka Koya ignimbrite.Sediments were recovered from 5 sites about 4.3 km off the northeastern side of Take-Shima Island. Each drilling site was separated by 10–20 m from any other site. The sediment was not consolidated. Bioturbation was not observed. The sediment sequence, from the top of the cores, consists of gravel unit, ill-sorted lapilli unit, reddish tephra unit, sandy silt unit, and white tephra unit. The sedimentary facies of these sediments is as follows.Gravel unit: The presence of this unit in the upper part of the sequence is suggested by gravels which fell in the drilling holes and recovered with the sediments of the lower sequence. The gravels are consist of white tuffaceous rock, obsidian, gray volcanic rock, reddish altered volcanic rock, gray pumice and altered pumice. They are angular to sub-angular in shape and varying in size up to 5 cm in diameter.Ill-sorted lapilli unit: This deposit consists of ill-sorted lapilli size light yellow colored pumices and lithics of dark volcanic rock, gray volcanic rock, and obsidian. The maximum grain size of the pumice is more than 5 cm, whereas the maximum grain size of the lithic is about 4 cm. The abundance of the pumice component varies with depth. The thickness of the unit is more than 7 m at the drilling sites. The color of the pumice suggests that this unit may be a secondary deposit of underlying Koya ignimbrite deposit.Reddish tephra unit: It consists of layers (maximum thickness at least 40 cm) of slightly reddish to orange ill-sorted pumice lapilli and thin layers (~1 cm thick) of relatively well-sorted ash. The thickness of the deposit is more than 5 m at the drilling sites. The characteristic color of pumice suggests that this unit is the deposit of Koya ignimbrite. Formation of relatively thin layers of lapilli and ash may be due to the deposition under the sea.Sandy silt unit: It consists of very fine fragments of black volcanic rock. The sediment contains small fragments (~5 mm) of sea shells and other organic materials. Foraminifars were also contained in this deposit. The thickness of this unit is at least 20.36 m.White tephra unit: This deposit mainly consists of ill-sorted white pumice lapilli and relatively well-sorted ash. The maximum pumice size is at least 11 cm. The thickness of the deposit is at least 30 m. The deposit is characterized by the presence of crystals of quartz, which is known as a remarkable feature of the Nagase ignimbrite deposit to distinguish it from the other tephra at Kikai volcano. Especially, the middle part of the recovered Nagase ignimbrite deposit (63–64 m below the seafloor) shows unique sedimentary face: it consists of only crystals of quartz (<2 mm in size), orthopyroxene and clinopyroxene (<1 mm in size), and magnetite (<2 mm in size). Formation of the sedimentary face may be due to the deposition of hot ignimbrite under the sea.Description of these sedimentary units is essential to distinguish the ignimbrite deposits and understand their flow behavior in the sea. We will show the detail of these sedimentary facies in the presentation.

著者

羽生 毅 小川 奈々子 大河内 直彦

出版者

国立研究開発法人海洋研究開発機構

雑誌

基盤研究(C)

巻号頁・発行日

2014-04-01

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炭素を含む揮発性成分の地球表層とマントルの間の循環過程はよく分かっていない。マントルに地球表層由来の炭素が存在するかどうかを検証するために、火山岩に含まれる炭素濃度と同位体を分析する技術開発を行った。二酸化炭素は火山岩が噴出するときに容易に脱ガスするため、ガスを保持していると考えられる海底噴出急冷ガラス試料を対象とした全岩分析と、火山岩中の斑晶に含まれるメルト包有物を対象とした局所分析を行った。この手法をマントル深部由来の海洋島玄武岩に応用した結果、一部の海洋島玄武岩には地球表層由来の炭素が含まれている可能性が示唆された。

著者

岩森 光 横山 哲也 中村 仁美 石塚 治 吉田 晶樹 羽生 毅 Tatiana Churikova Boris Gordeychik Asobo Asaah Festus T. Aka 清水 健二 西澤 達治 小澤 恭弘

出版者

国立研究開発法人海洋研究開発機構

雑誌

基盤研究(A)

巻号頁・発行日

2014-04-01

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全地球に分布する主に第四紀に噴火した玄武岩の組成に基づき、地球内部の不均質構造を調べた。これは人体の血液検査に例えることができる。特に、最近提案された「マントルの東西半球構造」に注目し、(1)半球構造の境界付近の詳細研究、(2)地球全体のデータに関する独立成分分析、(3)水を含むマントル対流シミュレーションを行った。その結果、東半球はより親水成分に富み、かつマントル浅部から内核にいたるまで、超大陸の分布に支配される「Top-down hemispherical dynamics」を介して長波長の大構造を有することが示唆された。