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

中西 正男

出版者

海洋調査技術学会

雑誌

海洋調査技術 (ISSN:09152997)

巻号頁・発行日

vol.23, no.1, pp.1_11-1_23, 2011 (Released:2011-06-06)

参考文献数

23

被引用文献数

1

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Field evaluation of sounding accuracy in the multi-narrow beam echosounder, SeaBeam 2112, on R/V Kairei was carried out in the seafloor with a depth of deeper than 9,000 m. Bathymetric data were gathered while the ship holds on station. Variations of pitch, roll, and heave indicate that the ship was so stable that the motion of the ship except for heading did not affect for soundings. The depth uncertainty in each beam was estimated by forming the ratio of the standard deviation of the soundings in each angular bin to their mean. The soundings in observation range from 8,500 m to 10,900 m. The uncertainty in most beams from beam angle -24° to 27° is below the quality assurance (< 0.5%) demanded by the manufacturer. That of outer beams from the beam angle -24° and 27° is larger than 0.5% because of beam pointing errors by motion of the ship and topographic relief. The uncertainty of all beams at a constant heading was lower than 0.5%. The depth uncertainty near the vertical beam was lower than 0.1%. Soundings by SeaBeam 2112 on R/V Kairei in deeper than 10,900 m of water depth satisfy Order 1b of Standards for Hydrographic Surveys (S-44) by the International Hydrographic Organization.

著者

古田 俊夫 藤本 博巳 中西 正男 村上 英幸

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.43, no.2, pp.233-241, 1990-06-24 (Released:2010-03-11)

参考文献数

5

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Acoustic digital data telemetry makes it possible to retrieve the observed values on a surface ship at any time during long-term underwater measurement. Several sea trials have been carried out totest feasibility and reliability of the telemetry by means of acoustic pulses from an ocean bottom heat flow meter newly developed for long-term measurement. More than 90% of values retrieved by the acoustic telemetry is in good agreement with ones memorized in the bottom equipment and recovered later. Bit length of each acoustic pulse for this data telemetry can be selected from 100msec to 10msec in accordance with the ambient acoustic noiselevel. Under normal sea states, 20msec is sufficient length of a pulse for the data retrieval from a depth of 6, 000 meters.

著者

中西 正男

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.126, no.2, pp.125-146, 2017

被引用文献数

4

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<p> A newly compiled bathymetric map including parts of the Kuril, Japan, and northern Izu–Ogasawara trenches in the northwestern Pacific Ocean demonstrates that most bending-related topographic structures are limited to less than 80 km from the trench axis. This observation contrasts with one that bending-related structures of eastern Pacific trenches are limited to less than 50 km from the trench axis. The discrepancy may be due to differences in the ages of subducting oceanic plates. Bending-related topographic structures of the western Kuril and southern Japan trenches are not parallel to the trench axis, but instead are parallel to magnetic anomaly lineations. Those of the northern Izu–Ogasawara Trench are parallel to fracture zones. These observations indicate the rule that the inherited seafloor spreading fabric is reactivated instead of forming new faults when the degree of obliquity between inherited seafloor spreading fabric and trench axis reaches about 30°. This rule is applicable to most trenches around the Pacific Ocean, except for some parts of curved trenches and trenches near seamounts or other volcanic edifices constructed by off-ridge volcanism. Most bending-related topographic structures near off-ridge volcanic edifices are parallel to the trench axis. This observation suggests that inherited seafloor spreading fabric around the volcanic edifies was disrupted by volcanism.</p>

著者

古田 俊夫 中西 正男

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.99, no.5, pp.490-506, 1990-10-25 (Released:2010-10-13)

参考文献数

59

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The discovery of the magnetic anomaly lineations that can give ages of ocean floor is a very important role for establishment of the plate tectonics theory. The magnetic anomaly lineations also give us information of a history of movements of the oceanic plates. However, the origin of magnetic anomaly lineations still been obscured, that is, we can not clearly answer for the following questions: How thick is the source layer of magnetic anomaly lineations? How strong is the intensity of the magnetic source layer? In this paper we examined the relevant information concerning the magnetization of the oceanic crust from studies of observed marine magnetic anomalies and from rock -magnetism of oceanic basalts to get a goal of these questions in this paper.The skewness parameter that is deduced by precise magnetic anomaly lineations is important to identify marine magnetic anomalies. The magnetic polarity transition width is also important to do, though the parameter associated with this transition width has not almost utilized in the previous works. The anomalous skewness and the skewness discrepancy are often observed over the oceans. These observations might be explained not by a single-layer model but a two-layer model for magnetic source layer. The polarity transition width is defined the width which 95.4 % of the change from normal to reversed polarity occurs within. This width increases monotonically with spreading rates of ridges and/or with ages of ocean floors. This increasing is considered to be a manifestation of a more complicated crustal source consisting of two discrete layers. The analysis of the skewness parameter and transition width strongly supports that the sourc elayer of marine magnetic anomalies has a two-layer structure. The upper layer, consisting of surface lava flows of layer 2 A and possibly the sheeted dike complex, hasdi stinct and approximately vertical magnetic in the vicinity of opposite magn etized region boundaries. The lower layer, consisting of intrusive and gabbroic layers, has the boundaries gradually sloping downward away from the spreading center.Many detailed survey are carried out to reveal the structure of magnetic source layer by the multi narrow and the deep-towed magnetometer near active ridges. Inversion of magnetic layer using results of detailed surveys concluded that the magnetic source layer near the active ridges is less than 1 km in thickness. The polarity transition width of the relatively young layer is narrower than that of older oceanic floor, and the magnetic intensity of the relatively young layers higher (more than 10A/m) than that of older one. These conclusion indicate that the magnetic source layer near the active ridg es consists of a single layer structure. It is thought that the magnetic source layer grows with ages asoceanic crust by results of analysis of skewness and polarity transition width and inversion of magnetic source layer near active ridges.Several previous paleomagnetic studies indicate that intensity of natural remanent magnetization (NRM) of basaltic rocks composing the ocean crust rapidly decreases with ages in the past 10 to 20 Ma, and gradually increases older one. This change in NRM intensity is roughly proportional to the changes in intensity of saturation magnetization of the rocks and possibly due to sea-water alteration (low-temperature oxidation) of the primary ferromagnetic minerals contained in the rocks. NRM of the oceanic rocks is initially thermoremanent magnetization acquired at the time of formation of the oceanic crust. In accordance with progressive oxidation, fraction of TRM to bulk intensity decreases, while that of the secondary magnetization increases.

著者

清水 祥伽 中西 正男 佐野 貴司

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2016年大会

巻号頁・発行日

2016-03-10

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応神ライズ海山群はシャツキーライズと天皇海山列の間に位置する海山群である。シャツキーライズはプルームヘッドによる多量の噴火によって148 Ma以降に形成されたと考えられている(Nakanishi et al., 1999)。シャツキーライズには3つの高まり(海台)、南からタム山塊、オリ山塊、シルショフ山塊が存在する。深海掘削試料の放射性年代から、タム山塊は144 Ma頃、オリ山塊は 134 Ma頃、シルショフ山塊は128 Ma頃に形成されたとされている(Geldmacher et al., 2014; Heaton and Koppers, 2014)。応神ライズ海山群周辺のプレートの年代は134 – 125 Maである(Nakanishi et al., 1999)が、その地形的特徴や形成時期についてはわかっていない。応神ライズ海山群は、シャツキーライズの主活動期の後しばらくしてから起こった火成活動で形成されたという仮説が提案されている(Sano, 2014)。応神ライズ海山群とシャツキーライズの形成の関係性が明らかになれば、マントルプルーム活動の変遷、特に主活動期の後の火成活動を理解することにつながる。2014 年7月に研究船「かいれい」による海底地形,重力,地磁気の地球物理学観測およびドレッジによる岩石採集が応神ライズ海山群において行われた(KR14-07航海)。本発表では、重力および海底地形の解析から明らかになった、応神ライズ海山群周辺の海洋地殻構造について報告する。使用したデータは、KR14-07航海で得られたマルチビームデータとSager et al. (1999)で作成された海底地形グリッドデータ、Sandwell and Smith (2009)で作成された衛星高度計観測から作成されたフリーエア重力異常データである。これらを用いて、地殻の厚さ及びアイソスタシーの状態、弾性層厚を求めた。海洋地殻の厚さはKuo and Forsyth (1988)の方法を用いてもとめた。また、アイソスタシー及び弾性層厚は海底地形とフリーエア重力異常に関するadmittance解析(McKenzie and Bowin, 1976)から求めた。解析結果から応神ライズ海山群の平均的地殻の厚さは12km程度であることが判明した。これは平均的な海洋地殻の6kmと比べ2倍も厚い。また、弾性層厚は2.6 kmであり、エアリータイプのアイソスタシーが成り立っていることが分かった。これらの解析結果から、応神ライズ海山群の形成年代は、周辺の海洋プレートの年代とほぼ同じであることが明らかになった。すなわち、応神ライズ海山群の形成時期は134 – 125 Maであると推定される。このことから、シルショフ海台形成と同年代にオージンライズ海山群が形成されたと考えられる。

著者

阿部 なつ江 馬場 聖至 荒井 章司 富士原 敏也 杉岡 裕子 鈴木 勝彦 山野 誠 平野 直人 中西 正男 道林 克禎 石川 正弘 町田 嗣樹 志藤 あずさ 伊藤 亜妃 仙田 量子 水上 知之 清水 健二 森下 知晃

出版者

独立行政法人海洋研究開発機構

雑誌

基盤研究(B)

巻号頁・発行日

2008

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海洋プレートの非活動域に発見された新種の火山「プチスポット火山」海域において、地球物理学的・地質学的調査および岩石試料採取を実施してきた。同試料・データは、東北沖日本海溝に沈み込む前の海洋プレートそのものであり、陸側プレートに与える影響や島弧における火山および地震活動を評価する上で、重要な試料・データをもとに、海洋プレートとその下のマントル構造について総合的な研究・調査を行った。