133 research outputs found
Geochemical characteristics of volcanic rocks from Conrad Rise, southern Indian Ocean: Insights into the origin of the plateaux at the Indian Ocean
No full textコンラッドライズはインド洋南部に存在する高まりである。これまでの多くの研究が、コンラッドライズを約9000 万年前に活動を開始したホットスポットと考えてインド洋
の構造発達史に組み入れている(Müller et al., 1993)が、対応するホットスポットトラックが不確定であり、ホットスポットではないとする研究結果(Courtillot et al., 2003)
もある。また、岩石学データは1980 年代に行われた一度の航海で得られた十数個の岩 石に限られ、化学組成からケルゲレン海台に似たマントル由来とされている(Borisova et
al., 1996)が、年代測定や同位体分析は行われていない。これまでに、学術研究船白鳳 丸KH-07-4 航海、KH-10-7 航海、KH-16-1 航海、KH-19-1 航海により地球物理観測とド
レッジによる試料採取が行われてきた。コンラッドライズ産の火山岩は塊状の溶岩、多孔質溶岩、火山岩角礫岩として産出し 主成分組成ではアルカリ玄武岩から強アルカリ粗面岩に区分され、非アルカリ岩の産出 は少ない。斑晶鉱物組み合わせはMg#が60 より高い試料ではカンラン石と単斜輝石で あり、60 より低い試料では単斜輝石、角閃石、黒雲母である。斜長石斑晶が含まれて いないことが特徴的である。しばしば、ゼノリスを含む。微量元素組成では、非アルカリ岩を除き、LREE などの液相濃集元素に富み、インド洋の海山や海台と似た組成を示 すが、微量元素比ではマリオン島やクロゼ諸島、ケルゲレン海台とは異なる。同位体組 成は、アルカリ岩については87Sr/86Sr が0.7045~0.7052、eNd が-0.9~-3.3、206Pb/204Pb が 17.7~18.6、207Pb/204Pb が15.52~15.56、208Pb/204Pb が37.9~38.8 となっている。D8/4 およびD 7/4 はそれぞれ、約70 と10 未満であるが、東側のレナ海山産の試料はD 8/4 が90、D 7/4 が12~13 とDupal 異常とみなせる値となっている。これらの特徴は、微量元素比 と同様に、マリオン島やクロゼ諸島、ケルゲレン海台とは異なる特徴である。類似した 特徴を持つ火成岩体としては、マダガスカル島のアルカリ岩(Mahoney et al. 1991)や
Afanasy-Nikitin ライズ(Mahoney et al., 1996; Borisova et al., 2001)が挙げられる 地磁気観測の結果に基づくテクトニクスの復元(T. Sato et al., 準備中)に基づけば、
コンラッドライズがデルカノ海膨やマダガスカル海台と一体となっていた時期がある と推定される。この時期にはAfanasy-Nikitin ライズも近傍に位置していたと考えられ、
同一の起源を持つ岩体の可能性が示唆される
Regional mantle heterogeneity regulates melt production along the Réunion hotspot-influenced Central Indian Ridge
No full textTo ascertain factors controlling melt production along a typical distal, 'hotspot-interacting' mid-ocean ridge, we investigated the extent and distribution of both plume-related and plume-unrelated basalt from the central Indian ridge (CIR) between 15°S and 20°S. Comprehensive geochemical data of fresh-quenched volcanic glasses and basalts were used. Variation of Sr, Nd, and Pb isotopic compositions and Nb/Zr, Ba/Nb, and Ba/La content were interpreted by mixing of three melt end members: the Indian depleted MORB mantle derived melt; radiogenic and enriched melt derived from source mantle for Rodrigues Ridge and the intermediate series of Mauritius Island (RE2, radiogenic enriched component 2); and radiogenic but depleted melt derived from source mantle for Gasitao Ridge (RD, radiogenic depleted component). On the basis of quantitative mantle melting and melt mixing model, results show that sources for RE2 and RD are geochemically distinct from those of the Réunion plume (RE1, radiogenic enriched melt component 1). Moreover, the geochemical variation of MORB of 15°S to 20°S is unrelated to contamination of the upper mantle by the Réunion plume. These results suggest strongly that plume-unrelated heterogeneity is widespread throughout the upper mantle. The chemical characteristics of RE2 are remarkably pronounced in basalt from the central portion of ridge segment 16 around 18°S, suggesting substantial magma production. The influence of RE2 decreases along with decreasing magma production to the north, and is only slightly identifiable in basalt from the northern part of segment 18. Although the influence of RE2 decreases somewhat to the south, basalts with extreme RE2 signature were produced in the center of segment 15 around 19°S, where magma production is high. In contrast to RE2, the geochemical signature of RD in basalt is geographically limited to two localities: the south end of segment 18 and the center of segment 15. However, these observations reveal that both RE2 and RD contribute strongly to magma production on segment 15. Results show that melting of ancient recycled plate materials with a low melting point regulates voluminous magma production along the CIR
Editorial for Special Issue “Deep-Sea Ferromanganese Nodules and Related Mineral Resources: Genesis, Exploration, and Mining”
No full textThe development of deep-sea ferromanganese nodules has the potential to provide critical metals for the creation of high-tech and green-tech technologies and devices [...
5.3 year time series of formation pore fluid pressure and temperature from IODP Hole 319-C0010A measured by GeniusPlug from 2010 to 2016
No full textOne primary objective of Integrated Ocean Drilling Program Expedition 365, conducted as part of the Nankai Trough Seismogenic Zone Experiment, was to recover a temporary observatory emplaced to monitor formation pore fluid pressure and temperature within a splay fault in the Nankai subduction zone offshore SW Honshu, Japan. Here we use a 5.3 year time series of formation pore fluid pressure, and in particular the response to ocean tidal loading, to evaluate changes in pore pressure and formation and fluid elastic properties induced by earthquakes. Our analysis reveals 31 earthquake‐induced perturbations. These are dominantly characterized by small transient increases in pressure (28 events) and decreases in ocean tidal loading efficiency (14 events) that reflect changes to formation or fluid compressibility. The observed perturbations follow a magnitude‐distance threshold similar to that reported for earthquake‐driven hydrological effects in other settings. To explore the mechanisms that cause these changes, we evaluate the expected static and dynamic strains from each earthquake. The expected static strains are too small to explain the observed pressure changes. In contrast, estimated dynamic strains correlate with the magnitude of changes in both pressure and loading efficiency. We propose potential mechanism for the changes and subsequent recovery, which is exsolution of dissolved gas in interstitial fluids in response to shaking
Geochemical characteristics of back-arc basin lower crust and upper mantle at final spreading stage of Shikoku Basin: an example of Mado Megamullion
No full textAbstract This paper explores the evolutional process of back-arc basin (BAB) magma system at final spreading stage of extinct BAB, Shikoku Basin (Philippine Sea) and assesses its tectonic evolution using a newly discovered oceanic core complex, the Mado Megamullion. Bulk and in-situ chemical compositions together with in-situ Pb isotope composition of dolerite, oxide gabbro, gabbro, olivine gabbro, dunite, and peridotite are presented. Compositional ranges and trends of the igneous and peridotitic rocks from the Mado Megamullion are similar to those from the slow- to ultraslow-spreading mid-ocean ridges (MOR). Since the timing of the Mado Megamullion exhumation corresponds to the very end of the Shikoku Basin opening, the magma supply was subdued and highly episodic, leading to extreme magma differentiation to form ferrobasaltic, hydrous magmas. In-situ Pb isotope composition of magmatic brown amphibole in the oxide gabbro is identical to that of depleted source mantle for mid-ocean ridge basalt (MORB). In the context of hydrous BAB magma genesis, the magmatic water was derived solely from the MORB source mantle. The distance from the back-arc spreading center to the arc front increased away through maturing of the Shikoku Basin to cause MORB-like magmatism. After the exhumation of Mado Megamullion along detachment faults, dolerite dikes intruded as a post-spreading magmatism. The final magmatism along with post-spreading Kinan Seamount Chain volcanism were introduced around the extinct back-arc spreading center after the opening of Shikoku Basin by residual mantle upwelling
Petit-spot as definitive evidence for partial melting in the asthenosphere caused by CO2
No full text地球のアセノスフェアは二酸化炭素によって部分的に溶けている : プレートテクトニクスの根幹に関わる論争決着に大きな前進. 京都大学プレスリリース. 2017-02-03.The deep carbon cycle plays an important role on the chemical differentiation and physical properties of the Earth's mantle. Especially in the asthenosphere, seismic low-velocity and high electrical conductivity due to carbon dioxide (CO2)-induced partial melting are expected but not directly observed. Here we discuss the experimental results relevant to the genesis of primitive CO2-rich alkali magma forming petit-spot volcanoes at the deformation front of the outer rise of the northwestern Pacific plate. The results suggest that primitive melt last equilibrated with depleted peridotite at 1.8 - 2.1 GPa and 1, 280 - 1, 290 °C. Although the equilibration pressure corresponds to the pressure of the lower lithosphere, by considering an equilibration temperature higher than the solidus in the volatile - peridotite system along with the temperature of the lower lithosphere, we conclude that CO2-rich silicate melt is always produced in the asthenosphere. The melt subsequently ascends into and equilibrates with the lower lithosphere before eruption
R/V Yokosuka "Cruise Report" YK19-05S
No full text調査海域: 南鳥島沖 / 調査期間: 2019年4月18日〜2019年4月28日Area: Off Minami-Torishima / Operation Period: April 18, 2019-April 28, 2019プチスポット火山活動から読み解くリソスフィアーアセノスフィア境界の実体とプレート変形過
R/V MIRAI Cruise Report MR16-07
No full text調査海域: 南鳥島周辺海域 / 調査期間: 2016年11月1日～2016年11月25日Area: Minamitorishima Island / Operation Period: November 1, 2016-November 25, 2016戦略的イノベーション創造プログラム(SIP)次世代海洋資源調査技術(海のジパング計画)「南鳥島周辺海域のレアアース泥広域調査」Cross-ministerial Strategic Innovation Promotion Program (SIP), New-generation Technology for Ocean Resources Exploration (ZIPANG in ocean), "Extensive investigation of REY-rich mud with the geophysical survey around the Minamitorishima offshore
Characteristics and Provenance of Basalts from the Continental Slope off Cape Darnley, East Antarctica: Evidence for Links to the West Antarctic Rift System
No full textThe 15th Symposium on Polar Science/Ordinary sessions [OG] Polar geosciences, Wed. 4 Dec. / 3F Conference room, National Institute of Polar Researchconference outpu
R/V Yokosuka "Cruise Report" YK17-11C
No full text調査海域: 南鳥島周辺海域 / 調査期間: 2017年5月28日〜2017年6月14日Area: Around Minamitorishima Island / Operation Period: May 28, 2017-June 14, 2017戦略的イノベーション創造プログラム(SIP)次世代海洋資源調査技術(海のジパング計画)「海洋資源の成因に関する科学的研究」による南鳥島周辺マンガンノジュール広域調
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