研究者詳細 - 田中　亮吏

論文 - 田中　亮吏

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The Albedo of Ryugu: Evidence for a High Organic Abundance, as Inferred from the Hayabusa2 Touchdown Maneuver 査読

Christian Potiszil, Ryoji Tanaka, Katsura Kobayashi, Tak Kunihiro, Eizo Nakamura

ASTROBIOLOGY 20 ( 7 ) 916 - 921 2020年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：MARY ANN LIEBERT, INC

The Hayabusa2 mission successfully collected samples from the asteroid Ryugu last year and will return these to Earth in December 2020. It is anticipated that the samples will enable the analysis of terrestrially uncontaminated organic matter and minerals. Such analyses are in turn expected to elucidate the evolution of organic matter through Solar System history, including the origination and processing of biogenically important molecules, which could have been utilized by the first organisms on Earth. In anticipation, studies have made predictions concerning the properties of Ryugu, including its composition. The spectral characteristics of Ryugu, such as albedo, have been employed to relate the asteroid to members of the carbonaceous chondrite group that have been identified on Earth. However, the recent Hayabusa2 touchdown highlights a disparity between the color of surfaces of displaced platy fragments, indicating a brightening trend for the surface exposed to space compared to that facing into the body. Here we present a mass balance calculation with reference to data from the literature, which indicates that Ryugu may contain a significantly higher abundance of organic matter (likely >50%) than the currently most accepted meteorite analogues. A high organic content may result in high levels of extractable organic matter for the second touchdown site, where the spacecraft sampled freshly exposed material. However, high abundances of insoluble aromatic/graphitic rich organic matter may be present in the first touchdown site, which sampled the surface of Ryugu that had been exposed to space. Moreover, we suggest that the potentially high organic abundance and the rubble-pile nature of Ryugu may originate from the capture of rocky debris by a comet nucleus and subsequent water-organic-mineral interactions and sublimation of water ice.

DOI： 10.1089/ast.2019.2198

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Concentration of meteoritic free organic matter by fluid transport and adsorption 査読

Christian Potiszil, Ryoji Tanaka, Tsutomu Ota, Tak Kunihiro, Katsura Kobayashi, Eizo Nakamura

Geochemical Perspectives Letters 13 30 - 35 2020年3月

掲載種別：研究論文（学術雑誌）

Carbonaceous chondrites contain many abiotic organic compounds, some of which are found in life on Earth. Both the mineral and organic matter phases, of these meteorites, have been affected by aqueous alteration processes. Whilst organic matter is known to be associated with phyllosilicate phases, no such relationship has yet been identified for specific organic compound classes. Furthermore, ongoing sample return missions, Hyabusa 2 and OSIRIS-Rex, are set to return potentially organic rich C-type asteroid samples to the Earth. Consequently, strategies to investigate organic-mineral relationships are required. Here we report spatial data for free/soluble organic matter (FOM/SOM) components (akylimidazole and alkylpyridine homologues) and mineral phases. Low and intermediate molecular weight alkylimidazole homologues are more widely distributed than higher molecular weight members, likely due to their affinity for the aqueous phase. On aqueous alteration of anhydrous mineral phases, transported FOM is adsorbed onto the surface or into the interlayers of the resulting phyllosilicates and thus concentrated and protected from oxidising fluids. Therefore, aiding the delivery of biologically relevant molecules to earth, shortly preceding the origin of life.

DOI： 10.7185/geochemlet.2010

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Triple oxygen isotope systematics as a tracer of fluids in the crust: A study from modern geothermal systems of Iceland 査読

D.O. Zakharov, I.N. Bindeman, R. Tanaka, G.Ó. Friðleifsson, M.H. Reed, R.L. Hampton

Chemical Geology 530 119312 - 119312 2019年12月

Tourmaline in a Mesoarchean pelagic hydrothermal system: Implications for the habitat of early life 査読

Tsutomu Ota, Yuhei Aihara, Shoichi Kiyokawa, Ryoji Tanaka, Eizo Nakamura

Precambrian Research 334 105475 - 105475 2019年11月

Transition from plume-driven to plate-driven magmatism in the evolution of the Main Ethiopian Rift 査読

Ryoji Tanaka

Journal of Petrology 2019年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

<jats:title>Abstract</jats:title><br />
<jats:p>New K-Ar ages, major and trace element concentrations, and Sr-Nd-Pb isotope data are presented for Oligocene to recent mafic volcanic rocks from the Ethiopian Plateau, the Main Ethiopian Rift (MER), and the Afar depression. Chronological and geochemical data from this study are combined with previously published data sets to reveal secular variations in magmatism throughout the entire Ethiopian volcanic region. The mafic lavas in these regions show variability in terms of silica-saturation (i.e., alkaline and sub-alkaline series) and extent of differentiation (mafic through intermediate to felsic). The P-T conditions of melting, estimated using the least differentiated basalts, reveal a secular decrease in the mantle potential temperature, from when the flood basalt magmas erupted (up to 1550 °C) to the time of the rift-related magmatism (&lt;1500 °C). Variations in the Sr-Nd-Pb isotopic compositions of the mafic lavas can account for the involvement of multiple end-member components. The relative contributions of these end-member components vary in space and time owing to changes in the thermal condition of the asthenosphere and the thickness of the lithosphere. The evolution of the Ethiopian rift is caused by a transition from plume-driven to plate-driven mantle upwelling, although the present-day mantle beneath the MER and the Afar depression is still warmer than normal asthenosphere.</jats:p>

DOI： 10.1093/petrology/egz043

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Asian dust increases radiocesium retention ability of serpentine soils in Japan. 査読国際誌

Nakao A, Tomita M, Wagai R, Tanaka R, Yanai J, Kosaki T

Journal of environmental radioactivity 204 86 - 94 2019年8月

Origin of ocean island basalts in the West African passive margin without mantle plume involvement 査読

Iyasu Getachew Belay, Ryoji Tanaka, Hiroshi Kitagawa, Katsura Kobayashi, Eizo Nakamura

Nature Communications 10 ( 1 ) 3022 2019年7月

A Method to Suppress Isobaric and Polyatomic Interferences for Measurements of Highly Siderophile Elements in Desilicified Geological Samples 査読

Xiaoyu Zhou, Ryoji Tanaka, Masahiro Yamanaka, Chie Sakaguchi, Eizo Nakamura

Geostandards and Geoanalytical Research 43 ( 4 ) 611 - 633 2019年7月

Hypervelocity collision and water-rock interaction in space preserved in the Chelyabinsk ordinary chondrite 査読

Nakamura E, Kunihiro T, Ota T, Sakaguchi C, Tanaka R, Kitagawa H, Kobayashi K, Yamanaka M, Shimaki Y, Bebout GE, Miura H, Yamamoto T, Malkovets V, Grokhovsky V, Koroleva O, Litasov K

Proceedings of the Japan Academy. Series B, Physical and biological sciences 95 ( 4 ) 165 - 177 2019年4月

The origin of the unique achondrite Northwest Africa 6704: Constraints from petrology, chemistry and Re–Os, O and Ti isotope systematics 査読

Hibiya Y, Archer GJ, Tanaka R, Sanborn ME, Sato Y, Iizuka T, Ozawa K, Walker RJ, Yamaguchi A, Yin QZ, Nakamura T, Irving AJ

Geochimica et Cosmochimica Acta 245 597 - 627 2019年1月

Circa 1 Ga sub-seafloor hydrothermal alteration imprinted on the Horoman peridotite massif 査読

Lalindra V. Ranaweera, Tsutomu Ota, Takuya Moriguti, Ryoji Tanaka, Eizo Nakamura

Scientific Reports 8 ( 1 ) 1 - 12 2018年6月

Silicate-SiO reaction in a protoplanetary disk recorded by oxygen isotopes in chondrules 査読

Ryoji Tanaka, Eizo Nakamura

NATURE ASTRONOMY 1 ( 7 ) 1 - 7 2017年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

The formation of planetesimals and planetary embryos during the earliest stages of the solar protoplanetary disk largely determined the composition and structure of the terrestrial planets. Within a few million years of the birth of the Solar System, chondrule formation and the accretion of the parent bodies of differentiated achondrites and the terrestrial planets took place in the inner protoplanetary disk(1,2). Here we show that, for chondrules in unequilibrated enstatite chondrites, high-precision Delta O-17 values (where Delta O-17 is the deviation of the delta O-17 value from a terrestrial silicate fractionation line) vary significantly (ranging from -0.49 to + 0.84%) and fall on an array with a steep slope of 1.27 on a three-oxygen-isotope plot. This array can be explained by the reaction between an olivine-rich chondrule melt and an SiO-rich gas derived from vaporized dust and nebular gas. Our study suggests that a large proportion of the building blocks of planetary embryos formed by successive silicate-gas interaction processes: silicate- H2O followed by silicate-SiO interactions under more oxidized and reduced conditions, respectively, within a few million years of the formation of the Solar System.

DOI： 10.1038/s41550-017-0137

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The oxygen isotope composition of San Carlos olivine on the VSMOW2-SLAP2 scale 査読

Andreas Pack, Ryoji Tanaka, Markus Hering, Sukanya Sengupta, Stefan Peters, Eizo Nakamura

RAPID COMMUNICATIONS IN MASS SPECTROMETRY 30 ( 13 ) 1495 - 1504 2016年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-BLACKWELL

RATIONALE: The precise determination of Delta'O-17 values in terrestrial material is becoming increasingly important to understand the mass-dependent fractionation processes that cause variations in oxygen isotope ratios. San Carlos olivine is widely used as the reference material for oxygen isotope measurements of terrestrial and extraterrestrial materials. We report new Delta'O-17 values for San Carlos olivine that were independently determined in two different laboratories (Geoscience Center [GZG], University of Gottingen) and Institute for Study of the Earth's Interior [ISEI], Okayama University, Misasa) in direct comparison with VSMOW2 and SLAP2 water standards.
METHODS: The delta O-17 and delta O-18 values of VSMOW2, SLAP2, GISP, and San Carlos olivine were determined relative to reference gas. In both laboratories, water and San Carlos olivine samples were prepared by BrF5 fluorination. In both laboratories, the O-2 released from water and olivine samples was passed through the same purification system and measured using the same mass spectrometer relative to the same reference gas.
RESULTS: In both laboratories, the delta O-17(VSMOW2) and delta O-18 (VSMOW2) scales were slightly compressed with respect to the recommended composition of VSMOW2 and SLAP2. The new Delta'O-17(0.528) value (calculated from the VSMOW2-SLAP2 scaled 6 values) of San Carlos olivine from GZG was -36 +/- 9 ppm and, from ISEI, a value of -40 +/- 7 ppm (1(7 standard deviation) was determined. These values are similar to 50 ppm higher than previously reported from the same laboratories. Possible causes for the observed discrepancies are discussed.
CONCLUSIONS: The results of this study in comparison with previous data from the same laboratories demonstrated that for high accuracy determination of Delta'O-17 values: (i) calibration of the reference gas relative to O-2 released from primary standards (VSMOW2, SLAP2) in the same laboratory is highly recommended, (ii) non-linearity of the mass spectrometer may not only affect delta O-17 and delta O-18 values but also Delta'O-17 values, and (iii) the VSMOW2-SLAP2 scaling should also be applied to analyses of rocks and minerals. Studies that are concerned with small differences in Delta'O-17 at similar delta O-18 values, however, are not affected by non-linearity of the mass spectrometer. Copyright (C) 2016 John Wiley & Sons, Ltd.

DOI： 10.1002/rcm.7582

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Aeolian-Dust-Derived Micaceous Minerals Control Radiocesium Retention in Andosols in Japan 査読

Atsushi Nakao, Aya Nakao, Ryoji Tanaka, Sho Ogasawara, Junta Yanai

SOIL SCIENCE SOCIETY OF AMERICA JOURNAL 79 ( 6 ) 1590 - 1600 2015年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SOIL SCI SOC AMER

Factors controlling the abilities of Allophanic Andosols (representative of Japanese volcanic ash soils) to retain radiocesium (RCs) were assessed. The hypothesis was that retention is largely controlled by traces of micaceous minerals deposited as components of aeolian dust. The radiocesium interception potentials (RIPs), mica K contents were determined in the 2- to 20- and <2.0-mm particle fractions of 23 soil samples from agricultural fields in areas representative of Japanese Allophanic Andosols. Quartz contents were determined in the 2- to 20-mm particle fractions of the same soil samples. The oxygen isotope ratio (delta O-18) in the quartz isolated from each 2- to 20-mm particle fraction was determined to identify the origin of the quartz in each soil sample. The mean RIP for the 2- to 20- and <2-mm particles was 1.7 +/- 0.8 and 2.6 +/- 1.3 mol kg(-1), respectively, and the mica K contents were 3.2 +/- 1.3 and 3.4 +/- 1.7 g kg(-1), respectively, corresponding to micaceous mineral contents of <5% by mass in each size fraction. In spite of their rather low values, the RIPs and mica K contents in each fraction positively correlated (p < 0.01), indicating that the abilities of the soils to retain RCs were mainly controlled by the micaceous mineral contents. The mica K content was proportional to the quartz content in the <20-mm particles, and the mean delta O-18 in the quartz was + 14.8%, similar to those in fine quartz in Chinese loess. These results strongly indicate that the abilities of Allophanic Andosols to retain RCs are largely controlled by micaceous minerals probably originating in aeolian dust.

DOI： 10.2136/sssaj2015.05.0173

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Evaluation of the applicability of acid leaching for the U-238-Th-230 internal isochron method 査読

Ryoji Tanaka, Tetsuya Yokoyama, Hiroshi Kitagawa, Demissie Bizuneh Tesfaye, Eizo Nakamura

CHEMICAL GEOLOGY 396 255 - 264 2015年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The U-238-Th-230 internal isochron method has great potential for determining eruption ages of young volcanic materials if the separated groundmass phases have a sufficiently wide range of U/Th ratios. We examined the fractionation behavior of U and Th in aged (i.e., >0.5 Ma) basaltic samples by 6 M hydrochloric acid leaching to evaluate the applicability of acid-leaching treatment for the U-238-Th-230 internal isochron method. Acid leaching of aged basaltic rocks in U-238-U-234-Th-230 secular equilibrium at the bulk-rock scale results in Th-230-U-238 and U-234-U-238 radioactive disequilibria for both leachates and residues. These radioactive disequilibria can be explained by redistribution of Th-234 (parent of U-234) and Th-230 between acid-soluble and acid-resistant phases due to alpha-recoil. The number of Th-230 atoms redistributed by alpha-recoil can be calculated by using a mass conservation equation for U-234 atoms and by the relative amount of recoiled Th-230 and Th-234, the latter proportional to the kinetic energy of the recoiled nuclide. When the fraction of daughter nuclide U-234 remaining in either the residue or leachate, after alpha-recoil redistribution of U-238, is large enough (>95%), the corrected (Th-230/U-238) values of leachate and residue show radioactive equilibria. This result demonstrates that preferential fractionation between U and Th does not occur during acid leaching for basaltic samples if there is no selective etching of the alpha-recoil track. This study implies that acid-leaching can be used in conjunction with the U-238-Th-230 internal isochron method for dating young volcanic rocks by evaluating the degree of the alpha-recoil redistribution of U-234. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemgeo.2014.12.025

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Oxygen isotopes in Indian Plate eclogites (Kaghan Valley, Pakistan): Negative δ18O values from a high latitude protolith reset by Himalayan metamorphism 査読

Rehman, Ur. H, Tanaka, R, O’Brien, J.P, Kobayashi, K, Tsujimori, T, Nakamura, E, Yamamoto, H, Khan, T, Kaneko, Y

Lithos 208 471 - 483 2014年11月

Two new eucrite breccias from Northwest Africa 査読

Sheryl A. Singerling, Aubrey L. Modi, Blake McFerrin, Emily A. Worsham, Harry Y. McSween, Douglas Rumble, Ryoji Tanaka, Lawrence A. Taylor

METEORITICS & PLANETARY SCIENCE 48 ( 2 ) E1 - E9 2013年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-BLACKWELL

This work describes two newly discovered eucrite breccias: three presumably paired meteorites, all named Northwest Africa (NWA) 6105, and NWA 6106. For each meteorite, major- and minor-element compositions of minerals were determined using the electron microprobe. Pyroxene Fe-Mn co-variations and bulk-rock oxygen isotope compositions confirm their classification as eucrites. Variations in mineral compositions and textures are attributed to differences in clast types present (i.e., basaltic or cumulate eucrite). The pyroxene compositions support the hypothesis that samples NWA 6105,1; 6105,2; and 6105,3 are paired polymict eucritic breccias, whereas sample NWA 6106 is a monomict basaltic eucritic breccia. Two-pyroxene geothermometry yields temperatures too low for igneous crystallization. The variation in temperatures among samples suggests that metamorphism occurred prior to brecciation.

DOI： 10.1111/maps.12025

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Determination of 17O-excess of terrestrial silicate/oxide minerals with respect to Vienna Standard Mean Ocean Water (VSMOW) 査読

Ryoji Tanaka, Eizo Nakamura

RAPID COMMUNICATIONS IN MASS SPECTROMETRY 27 ( 2 ) 285 - 297 2013年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-BLACKWELL

RATIONALE Oxygen triple isotope compositions give key information for understanding physical processes during isotopic fractionation between the geo-, hydro-, bio-, and atmosphere. For detailed discussion of these topics, it is necessary to determine precise 17O-excess values of terrestrial silicate/oxide minerals with respect to Vienna Standard Mean Ocean Water (VSMOW). METHODS Water was fluorinated in an electrically heated Ni-metal tube into which water and BrF5 were loaded for the quantitative extraction of oxygen. Silicate/oxide minerals were fluorinated by heating with a CO2 laser in an atmosphere of BrF5. The extracted oxygen was purified and isotope ratios of the oxygen triple isotope compositions were determined using a Finnigan MAT253 isotope ratio mass spectrometer. RESULTS The oxygen triple isotope compositions of meteoric water and terrestrial silicate/oxide minerals fall on statistically distinguishable fractionation lines, defined as [ln(d17O?+?1)?=??ln(d18O?+?1)?+??], where ? and ? correspond to the slope and intercept, respectively. The fractionation line for meteoric water has ??=?0.5285?+/-?0.0005 and ??=?0.03?+/-?0.02 parts per thousand and for terrestrial silicate/oxide minerals has ??=?0.5270?+/-?0.0005 and ??=?0.070?+/-?0.005 parts per thousand, at the 95% confidence limit. CONCLUSIONS All the analyzed terrestrial silicate/oxide minerals including internationally accepted reference materials (NBS-28, UWG-2, and San Carlos olivine) have a negative 17O-excess with respect to VSMOW. We propose that it is necessary to specify if the determined d17O values of terrestrial and extraterrestrial samples are expressed as the difference from VSMOW or the terrestrial silicate mineral-corrected value. Copyright (c) 2012 John Wiley & Sons, Ltd.

DOI： 10.1002/rcm.6453

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Inherited Pb isotopic records in olivine antecryst-hosted melt inclusions from Hawaiian lavas 査読

Patrick Asamoah Sakyi, Ryoji Tanaka, Katsura Kobayashi, Eizo Nakamura

GEOCHIMICA ET COSMOCHIMICA ACTA 95 169 - 195 2012年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Dislocation textures of olivine grains and Pb isotopic compositions (Pb-207/Pb-206 and Pb-208/Pb-206) of olivine-hosted melt inclusions in basaltic lavas from three Hawaiian volcanoes (Kilauea, Mauna Loa, and Koolau) were examined. More than 70% of the blocky olivine grains in the studied samples have a regular-shaped dislocation texture with their dislocation densities exceeding 10(6) cm(-2), and can be considered as deformed olivine. The size distribution of blocky olivine grains shows that more than 99% of blocky olivines coarser than 1.2 mm are identified as deformed olivine. These deformed olivine grains are identified as antecrysts, which originally crystallized from previous stages of magmatism in the same shield, followed by plastic deformation prior to entrainment in the erupted host magmas. This study revealed that entrainment of mantle-derived crystallization products by younger batches of magma is an important part of the evolution of magnesium-rich Hawaiian magma. Lead isotopic compositions of melt inclusions hosted in the olivine antecrysts provide information of the evolutionary history of Hawaiian volcanoes which could not have been accessed if only whole rock analyses were carried out. Antecryst-hosted melt inclusions in Kilauea and Koolau lavas demonstrate that the source components in the melting region changed during shield formation. In particular, evidence of interaction of plume-derived melts and upper mantle was observed in the earliest stage of Koolau magmatism. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2012.07.025

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PETROLOGIC, ELEMENTAL AND OXYGEN ISOTOPIC CHARACTERIZATION OF HIGHLY ENRICHED MAFIC SHERGOTTITE NORTHWEST AFRICA 7257 査読

A. J. Irving, S. M. Kuehner, G. Chen, C. D. K. Herd, R. Tanaka, D. A. Gregory

METEORITICS & PLANETARY SCIENCE 47 A209 - A209 2012年7月

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