著者

松野 哲男 巽 好幸 島 伸和 鈴木 桂子 市原 寛 清杉 孝司 中岡 礼奈 清水 賢 佐野 守 井和丸 光 両角 春寿 杉岡 裕子 中東 和夫 山本 揚二朗 林 和輝 西村 公宏 古川 優和 堀内 美咲 仲田 大地 中村 崚登 廣瀬 時 瀬戸 康友 大重 厚博 滝沢 秀明 千葉 達朗 小平 秀一

出版者

日本地球惑星科学連合

雑誌

日本地球惑星科学連合2018年大会

巻号頁・発行日

2018-03-14

---

We started integrated marine investigations of Kikai Caldera with T/S Fukae-maru of Kobe University on October, 2016. Aims of our investigations are to reveal the structure of the caldera, the existence of magma reservoir, and to understand the mechanism of catastrophic caldera-forming eruption at 7.3 ka and a potential for a future catastrophic eruption. We conducted multi-beam echo sounder mapping, multi-channel seismic reflection (MCS) surveys, remotely operated vehicle (ROV) observations, rock sampling by dredging and diving, geophysical sub-seafloor imaging with ocean bottom seismometers, electro-magnetometers (OBEMs), some of which equip absolute pressure gauge, ocean-bottom magnetometers, and surface geomagnetic surveys.The first finding of our investigations is lines of evidence for creation of a giant rhyolite lava dome (~32 km3) after the caldera collapse. This dome is still active as water column anomalies accompanied by bubbling from its surface are observed by the water column mapping. Chemical characteristics of dome-forming rhyolites akin to those of presently active small volcanic cones are different from those of supereruption. The voluminous post-caldera activity is thus not caused simply by squeezing the remnant of syn-caldera magma but may tap a magma system that has evolved both chemically and physically since the 7.3-ka supereruption.We have been conducting integrated analyses of our data set, and have planned the fourth research cruise with T/S Fukae-maru on March, 2018, consisting of MCS survey, ROV observation, OBEM with absolute pressure gauge observation, and bathymetric and surface geomagnetic survey. We will introduce results of the data analyses and the upcoming cruise in the presentation.

著者

巽 好幸

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.110, no.4, pp.244-250, 2004 (Released:2005-01-07)

参考文献数

29

被引用文献数

2 1

---

島弧の進化に関して, 検証可能な作業仮説を提示する. 初期マグマ活動によって形成された玄武岩質島弧地殻は, 下部地殻の部分融解により, 下部のマフィックな部分と上部の安山岩質の部分に分化する. 前者は, 島弧衝突過程で相転移を主要な原動力として分離され, 安山岩質の大陸地殻が誕生する. さらに成熟した島弧では, 安山岩質地殻の部分融解により, フェルシックマグマが生産される. IODPとその関連研究によって, この作業仮説の検証を試みる.

著者

巽 好幸 末永 伸明 吉岡 祥一 金子 克哉

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.585-597, 2021-08-25 (Released:2021-09-23)

参考文献数

58

被引用文献数

2 2

---

Water circulation, along with plate subduction, is considered based on the stabilities of hydrous phases and pressure–temperature profiles of the sinking oceanic plate. Water in a rather hot slab like the present one may be largely liberated at shallow depths (< 150 km) and return to the ocean via. arc magmatism. On the other hand, stabilization of dense hydrous minerals under cooler conditions, which current subduction zones will soon experience, causes the transportation or reflux of seawater to the deep mantle, which reduces the total mass of surface seawater. Simple calculations accepting water contents in the subducting slab suggested by a recent seismic velocity structure model indicate that the Earth's oceans are likely to disappear ∼80 million years hence. Significant changes may happen such as the end of plate tectonics and the onset of snowball Earth, with associated catastrophes affecting life. The only way to confirm this picture of the future of the ocean planet Earth is to examine deep hydration taking place along the outer rise through direct analyses of the upper mantle across the Moho.

著者

巽 好幸 柵山 雅則 福山 博之 久城 育夫

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集 (ISSN:24330590)

巻号頁・発行日

vol.27, no.1, pp.45-65, 1982-04-30 (Released:2018-01-15)

---

The compositions of the primary tholeiitic, high-alumina and alkali-olivine basalt magmas (THB, HAB and AOB magmas, respectively) which are derived directly from the upper mantle beneath the volcanic arcs, are obtained by calculating the average compositions of liquid in equilibrium with the mantle peridotite, which can produce basalts in NE Japan arc through olivine maximum fractionation. Anhydrous high-pressure melting experiments on these three basalts indicate that the AOB and HAB magmas coexist with olivine, orthopyroxene and clinopyroxene at 1360℃ and 17.5 kbar and at 1340℃ and 15 kbar, respectively. The THB magma, on the other hand, coexists with olivine and orthopyroxene at 1320℃ and 11 kbar. The volcanic arc magmas are believed to contain significant amounts of water which affect the P-T conditions of the phase equilibria at high temperatures and pressures. However, the detailed petrographic studies on the rock suites in volcanic arcs revealed that the island arc primary basalt magmas contain water not more than 3 wt.% at generation in the upper mantle. Combining this with the experimental results, the THB, HAB and AOB magmas are suggested to segregate from the mantle at temperatures of about 1300℃ and at pressures of 11 kbar (THB), 16 kbar (HAB) and 20 kbar (AOB), respectively. As the temperatures of segregation of the magmas given above are too high for a stable mantle geotherm, the mantle diapir is the most probable mechanism for magma generation under the volcanic arcs. Due to the heat of formation of liquid in the diapir, the temperature of the diapiric mantle must be higher at deeper levels. The required temperature of the upper mantle is 1400℃ at a certain depth between the descending slab and depth of approximately 70km.

著者

巽 好幸 後藤 篤 須藤 章

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 1988.2 (ISSN:24335320)

巻号頁・発行日

pp.80, 1988-11-29 (Released:2017-02-10)

著者

巽 好幸 谷 健一郎 川畑 博

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.115, no.Supplement, pp.S15-S20, 2009 (Released:2012-01-26)

参考文献数

16

被引用文献数

1 1

---

小豆島には,瀬戸内火山帯の一部をなす中新世の火山岩類(瀬戸内火山岩類)が分布する.これらは,他地域の瀬戸内火山岩類と比べて以下の特徴を有する:(1)比較的規模の大きい複成火山体をなす.(2)水中火山活動の証拠が顕著に認められる.(3)玄武岩から流紋岩までの広い化学組成を有する.(4)斑状火山岩と比較的無斑晶質な火山岩(サヌキトイド)まで,岩相変化に富む.(5)サヌキトイドの複合溶岩流が存在する.(6)初生的な安山岩(高Mg安山岩),玄武岩が産する.ここでは,主にこれらの特徴を簡略に説明する.

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

---

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

周藤 正史 宇都 浩三 味喜 大介 石原 和弘 巽 好幸

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B (ISSN:0386412X)

巻号頁・発行日

vol.43, no.B-1, pp.15-35, 2000-04-01

---

姶良カルデラにおいて2万5千年前に起こった, 爆発的な姶良火砕噴火に至るまでの火山活動をK‐Ar年代測定法により調べた。姶良カルデラ縁に分布する火山岩32試料のK-Ar年代値によると, (1)3‐lMaにカルデラ南北縁で安山岩質, (2)1‐0.4Maに北西縁で玄武岩‐流紋岩質, (3)0.4‐0.1Maに南西縁で玄武岩‐流紋岩質, (4)0.1‐0.025Maに北縁で安山岩質, 及び南北線でほぼ同時期に流紋岩質の活動が起こった。姶良カルデラ直下において現在存在が推定される流紋岩質マグマ溜まりは(4)の時期には既に存在していたのかもしれない。キーワード:姶良カルデラ, K。Ar年代測定, 火山活動史, 爆発的噴火, マグマ溜まり

著者

西原 歩 巽 好幸 鈴木 桂子 金子 克哉 木村 純一 常 青 日向 宏伸

出版者

日本地球惑星科学連合

雑誌

日本地球惑星科学連合2018年大会

巻号頁・発行日

2018-03-14

---

破局的カルデラ形成噴火を生じる膨大な珪長質マグマの起源を理解するために,3万年前に生じた姶良火砕噴火で噴出した入戸火砕流中に含まれる本質岩片の地球化学的・岩石学的特徴を考察した.流紋岩質の白色軽石及び暗色軽石に含まれる斜長石斑晶のコア組成は~An85と~An40にピークを持つバイモーダルな分布を示すことに対して,安山岩質スコリアの斜長石斑晶は~An80にピークを持つユニモーダルな分布を示す.高An(An#=70-90)と低An(An#=30-50)斜長石コアのストロンチウム同位体比は,それぞれ87Sr/86Sr=0.7068±0.0008,0.7059±0.0002である.これらの測定結果は,姶良火砕噴火で噴出した膨大な量の流紋岩質マグマは,高An斜長石の起源である安山岩質マグマと低An斜長石の起源である珪長質マグマの混合によって生じたことを示唆する.苦鉄質マグマからわずかに分化してできた考えられる安山岩質マグマから晶出した斜長石のSr同位体比は,中新世の花崗岩や四万十累層の堆積岩など,高いSr同位体比をもつ上部地殻の岩石を同化したトレンドを持つ.このことは,安山岩質マグマと珪長質マグマの混合が上部地殻浅部で生じたことを示唆する.また,流紋岩質マグマは基盤岩より斜長石中のSr同位体比が低く,基盤岩との同化をほぼ生じていない安山岩質マグマ(英文にあわせてみました)と似たような組成を持つ.このことは,珪長質マグマと苦鉄質マグマは,姶良カルデラ深部の下部地殻のような同一の起源物質から生じているとして説明できる.

著者

荒牧 重雄 柵山 雅則 早川 由紀夫 中村 保夫 巽 好幸

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.26, no.2, 1981-07-01

著者

能田 成 村崎 充弘 巽 好幸

出版者

一般社団法人 日本質量分析学会

雑誌

Journal of the Mass Spectrometry Society of Japan (ISSN:13408097)

巻号頁・発行日

vol.38, no.3, pp.125-131, 1990 (Released:2007-05-01)

被引用文献数

1 1

---

Isotopic compositions of Sr and Nd were determined for the volcanic rocks from the Izu Islands Arc. The volcanic rocks from the volcanic front zone show variable Nd isotopes ranging from 0.513088 to 0.513125 of 143Nd/144Nd with an average εNd of 9.0±0.3, and 87Sr/86Sr from 0.70318 to 0.70355 with an average εSr of -16.1±0.7. The back arc side volcanics show slightly lower Nd and Sr isotopic ratios as 143Nd/144Nd from 0.512994 to 0.513066 with an average εNd of 7.8±0.4 and 87Sr/86Sr form 0.70299 to 0.70325 with average εSr of -19.9±0.4. Across arc isotopic variation of Sr and Nd from the volcanic front to the back-arc side is attributed to difference in the degree that the magmas of the subduction zones are generated by the addition of the fluid which is extracted from the hydrous minerals in the down-going slab. Magmas in the volcanic front are much more affected by the addition of the considerable amount of the fluid than the back-arc side magmas and altered Sr and Nd isotopic compositions from their original values of the mantle wedge. The role of the fluid from the down-going slab for magma generation is isotopically assessed in the intra-oceanic Izu arc, and the Nd and Sr isotopic compositions of the fluid extracted from the down-going slab is equivalent with those of the altered MORB.