著者

吉崎 もと子 渋谷 岳造 鈴木 勝彦 清水 健二 中村 謙太郎 大森 聡一 高井 研 丸山 茂徳

出版者

一般社団法人日本地球化学会

雑誌

日本地球化学会年会要旨集 2011年度日本地球化学会第58回年会講演要旨集

巻号頁・発行日

pp.58, 2011 (Released:2011-09-01)

---

様々な分野の研究から、初期地球の熱水系にはメタン生成菌のような水素をエネルギー源とする化学合成独立栄養細菌を一次生産者に持つ生態系が繁栄しており、水素は生命誕生・進化の重要な鍵であったと考えられる。本研究では、初期地球熱水系では当時の表層にあったとされるAl枯渇型コマチアイトが水素発生を担っていたと考え、熱水実験を通して初期地球のコマチアイト熱水系における水素発生量とその反応過程を検証した。その結果、コマチアイトの熱水変質による顕著な水素発生量を確認した。また、実験生成物の分析を行った結果、かんらん石では従来提唱されてきたように蛇紋石化反応に伴う磁鉄鉱生成によって水素が発生しているのに対し、コマチアイトでは別の水素発生プロセスが進行し、それは、粘土鉱物への?V価鉄の分配によるH2Oの還元であると推定した。コマチアイトの熱水変質による水素発生量は、現生のかんらん岩熱水系で観測される水素濃度に匹敵し、現世のかんらん岩熱水系と同様に、初期地球熱水系の生態系に豊富な量の水素を供給していたことが示唆される。

著者

鈴木 和恵 丸山 茂徳 山本 伸次 大森 聡一

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.119, no.6, pp.1173-1196, 2010-12-25 (Released:2011-03-17)

参考文献数

48

被引用文献数

20 35

---

The Japanese Islands have long been considered to be the most evolved of all the island arcs in the oceans. A simple scenario has been implicitly accepted for the growth of the Japanese Islands: since subduction started sometime around 520 Ma, the TTG crust has increased over time in association with the steady-state growth of the accretionary prism in front. Here, we show very different dynamic growths of TTG crusts over time than previously thought, i.e., four times more TTG crusts than at present must have gone into the deep mantle due to tectonic erosion, which occurred six times since subduction was initiated at 520 Ma. Tectonic erosion is a major process that has controlled the development history of the Japanese islands. It can be traced as a serpentinite mélange belt, which indicates the upper boundary of past extensive tectonic erosion.

著者

丸山 茂徳 大森 聡一 千秋 博紀 河合 研志 B.F. WINDLEY

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.120, no.1, pp.115-223, 2011-02-25 (Released:2011-05-20)

参考文献数

217

被引用文献数

26 42 22

---

Pacific-type orogeny (PTO) has long been recognized as a contrasting accretionary alternative to continent-continent collisional orogeny. However, since the original concept was proposed, there have many new developments, which make it timely to produce a new re-evaluated model, in which we emphasize the following new aspects. First, substantial growth of Tonarite–Trondhjemite–Granite (TTG) crust, and second the reductive effect of tectonic erosion. The modern analog of a Pacific-type orogen developed through six stages of growth exemplified by specific regions; initial stage 1: the southern end of the Andes; stage 2: exhumation to the mid-crustal level at Indonesia outer arc; stage 3: the Barrovian hydration stage at Kii Peninsula, SW Japan; stage 4: the initial stage of surface exposure of the high-P/T regional metamorphic belt at Olympic Peninsula, south of Seattle, USA; stage 5: exposure of the orogenic core at the surface at the Shimanto metamorphic belt, SW Japan; and stage 6: post-orogenic processes including tectonic erosion at the Mariana and Japan trench and the Nankai trough. The fundamental framework of a Pacific-type orogen is an accretionary complex, which includes limited ocean floor material, much terrigenous trench sediment, plus island arc, oceanic plateau, and intra-oceanic basaltic material from the ocean. The classic concept of a PTO stresses the importance of the addition within accreted rocks of new subduction-generated arcs and TTGs, which were added along the continental margins particularly during the Cretaceous. Besides the above additional or positive aspects of a PTO, here we emphasize the negative effects of previously little-considered tectonic erosion caused by subduction over time. The evaluation of such extensive tectonic erosion leads a prospect of the presence of huge quantities of TTG material in the lower transition zone, where many subducted slabs have ponded, as illustrated by mantle tomography. This is confirmed by density profiles of the mantle, which show that TTGs are abundant only along the bottom of the upper mantle accompanied by slab peridotite, lherzolite, and MORB. The major velocity anomaly in the lower transition zone is best explained by the predominance of SiO2 phases, hence TTG, and not by MORB or ultramafic rocks. Reasonable calculations indicate that at a depth range of 520-660 km TTG material amounts to 6-7 times more than the total mass of the surface continental crust. The traditional view is that the Japanese islands evolved since 520 Ma through five Pacific-type orogenies, which grew oceanward, thus creating a continuous accretionary complex ca. 400-500 km wide, with TTG growth at the continental side of each orogen. However, the subducting oceanic lithosphere has produced five times more TTG crust compared with the present TTG crust in the Japan islands. This is explained by the fact that over time tectonic erosion has dominated the increasing arc-TTG crust. Accordingly, Japan has lost four arc-TTG crusts to tectonic erosion. TTG material, such as trench sediment, arc crust, and continental margin crust, was fragmented by tectonic erosion and transported into the bottom of the upper mantle at depths of 520-660 km. Worldwide data suggest that tectonic erosion destroyed and fragmented most of the Pacific-type orogens.(View PDF for the rest of the abstract.)

著者

吉屋 一美 佐藤 友彦 大森 聡一 丸山 茂徳

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.128, no.4, pp.625-647, 2019-08-25 (Released:2019-09-20)

参考文献数

77

被引用文献数

4 4

---

The Hadean surface was mainly covered by three kinds of rock: komatiite, KREEP basalt, and anorthosite, which were remarkably different from those on the modern Earth. Water–rock interactions between these rocks and water provided a highly reducing environment and formed secondary minerals on the rock surface that are important for producing metallo-enzymes for the emergence of primordial life. Previous studies suggest a correlation with active sites of metallo-enzymes and sulfide minerals based on an affinity with their structure, but they do not discuss the origins of metallic elements contained in these minerals, which are critical to understand where primordial life was born. Secondary minerals formed through water–rock interactions of komatiite in a nuclear geyser system are investigated, followed by a discussion of the relationship between active sites of metallo-enzymes and secondary minerals. Instead of komatiite, we used serpentinite collected from Hakuba Happo area, Nagano Prefecture in central-north Japan, which is thought to be one of the Hadean modern analogues for the birthplace of life. Several minor minerals were found, including magnetite, chromite, pyrite, and pentlandite, in addition to the major serpentine minerals. Pentlandite is not been mentioned in previous studies as a candidate for supplying important metallic elements to form metallo-enzymes in previous studies. It also acts as a catalyst for hydrogen generation, because it closely resembles the structural features of an active site of hydrogenases. Nickel-iron sulfide, pentlandite, is considered to be one of the important minerals for the origin of life. In addition, what kinds of minor mineral would be obtained from water–rock interactions of these rocks is estimated using a thermo-dynamic calculation. KREEP basalt contains large amounts of iron, and it could be useful for producing metallo-enzymes, especially for ferredoxins, an electron transfer enzymes associated with the emergence of primordial life.

著者

丸山 茂徳 横山 哲也 澤木 佑介 大森 聡一 鳴海 一成 ドーム ジェームズ 丹下 慶範

出版者

東京工業大学

雑誌

新学術領域研究(研究領域提案型)

巻号頁・発行日

2014-07-10

---

本計画研究班では、地球史研究から導かれる「生命誕生の器」としての原始地球表層環境を定量的に復元し、冥王代地球表層環境進化の過程を具体的に解明することを目的としている。H29年度の研究は主に5つのテーマで実施された。[1]生命誕生場と生命誕生のプロセスの解明:生命が誕生するためには、水があるだけでは不十分で、それ以外にも複数の環境条件が満たされることが必要である。そこで、諸条件の中から生命誕生場に必要な9つの条件を抽出してまとめた。[2]白馬地域の地質の継続調査と古環境の分類:冥王代類似環境としての白馬地域の特殊な水環境について比較分析し、水環境場を4つのタイプに分類した。白馬で特徴的な蛇紋岩熱水系温泉水は、高アルカリかつ水素ガスを大量に含んでおり、特に、H2を含むため貧酸素水であり、そのため冥王代型の微生物生態系が形成されていることが明らかになった。[3]オクロの自然原子炉の研究:ガボン国内の数地域で露頭周辺の調査を集中的に行い、最適と思われる掘削地点を三か所抽出した。[4]地球の起源と新たな太陽系惑星形成論の展開:太陽系進化の初期条件を決めるうえで、太陽系組成ガスから凝縮した最古の物質であるCAIの理解を深めることが重要である。そこで、始原的隕石ALLENDEに含まれる3種類のCAIに注目し、それらの核合成起源Sr同位体異常(μ84Sr)を高精度で測定した。その結果、μ84Sr値の大きさはFTA > Type B > FSの順であることが判明した。[5]継続的なブレインストーミングの実施:2件の国際ワークショップと4件の国内向けワークショップ実施した。

著者

丸山 茂徳 大森 聡一 千秋 博紀 河合 研志 WINDLEY B. F.

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.120, no.1, pp.115-223, 2011-02-25

被引用文献数

5 42

---

Pacific-type orogeny (PTO) has long been recognized as a contrasting accretionary alternative to continent-continent collisional orogeny. However, since the original concept was proposed, there have many new developments, which make it timely to produce a new re-evaluated model, in which we emphasize the following new aspects. First, substantial growth of Tonarite–Trondhjemite–Granite (TTG) crust, and second the reductive effect of tectonic erosion. The modern analog of a Pacific-type orogen developed through six stages of growth exemplified by specific regions; initial stage 1: the southern end of the Andes; stage 2: exhumation to the mid-crustal level at Indonesia outer arc; stage 3: the Barrovian hydration stage at Kii Peninsula, SW Japan; stage 4: the initial stage of surface exposure of the high-P/T regional metamorphic belt at Olympic Peninsula, south of Seattle, USA; stage 5: exposure of the orogenic core at the surface at the Shimanto metamorphic belt, SW Japan; and stage 6: post-orogenic processes including tectonic erosion at the Mariana and Japan trench and the Nankai trough.<br> The fundamental framework of a Pacific-type orogen is an accretionary complex, which includes limited ocean floor material, much terrigenous trench sediment, plus island arc, oceanic plateau, and intra-oceanic basaltic material from the ocean. The classic concept of a PTO stresses the importance of the addition within accreted rocks of new subduction-generated arcs and TTGs, which were added along the continental margins particularly during the Cretaceous. Besides the above additional or positive aspects of a PTO, here we emphasize the negative effects of previously little-considered tectonic erosion caused by subduction over time. The evaluation of such extensive tectonic erosion leads a prospect of the presence of huge quantities of TTG material in the lower transition zone, where many subducted slabs have ponded, as illustrated by mantle tomography. This is confirmed by density profiles of the mantle, which show that TTGs are abundant only along the bottom of the upper mantle accompanied by slab peridotite, lherzolite, and MORB. The major velocity anomaly in the lower transition zone is best explained by the predominance of SiO₂ phases, hence TTG, and not by MORB or ultramafic rocks. Reasonable calculations indicate that at a depth range of 520-660 km TTG material amounts to 6-7 times more than the total mass of the surface continental crust.<br> The traditional view is that the Japanese islands evolved since 520 Ma through five Pacific-type orogenies, which grew oceanward, thus creating a continuous accretionary complex <i>ca.</i> 400-500 km wide, with TTG growth at the continental side of each orogen. However, the subducting oceanic lithosphere has produced five times more TTG crust compared with the present TTG crust in the Japan islands. This is explained by the fact that over time tectonic erosion has dominated the increasing arc-TTG crust. Accordingly, Japan has lost four arc-TTG crusts to tectonic erosion. TTG material, such as trench sediment, arc crust, and continental margin crust, was fragmented by tectonic erosion and transported into the bottom of the upper mantle at depths of 520-660 km. Worldwide data suggest that tectonic erosion destroyed and fragmented most of the Pacific-type orogens.<br>(View PDF for the rest of the abstract.)

著者

鈴木 和恵 丸山 茂徳 山本 伸次 大森 聡一

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.6, pp.1173-1196, 2010-12-25

被引用文献数

11 35

---

The Japanese Islands have long been considered to be the most evolved of all the island arcs in the oceans. A simple scenario has been implicitly accepted for the growth of the Japanese Islands: since subduction started sometime around 520 Ma, the TTG crust has increased over time in association with the steady-state growth of the accretionary prism in front. Here, we show very different dynamic growths of TTG crusts over time than previously thought, <i>i.e.</i>, four times more TTG crusts than at present must have gone into the deep mantle due to tectonic erosion, which occurred six times since subduction was initiated at 520 Ma. Tectonic erosion is a major process that has controlled the development history of the Japanese islands. It can be traced as a serpentinite mélange belt, which indicates the upper boundary of past extensive tectonic erosion.