Updated on 2025/03/12

写真a

 
NAKANISHI, Nao
 
Affiliation
Faculty of Education and Integrated Arts and Sciences, School of Education
Job title
Assistant Professor(without tenure)

Research Experience

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    日本地球化学会

 

Papers

  • Zirconium isotope composition indicates s‐process depletion in samples returned from asteroid Ryugu

    Maria Schönbächler, Manuela A. Fehr, Tetsuya Yokoyama, Ikshu Gautam, Nao Nakanishi, Yoshinari Abe, Jérôme Aléon, Conel Alexander, Sachiko Amari, Yuri Amelin, Ken‐ichi Bajo, Martin Bizzarro, Audrey Bouvier, Richard W. Carlson, Marc Chaussidon, Byeon‐Gak Choi, Nicolas Dauphas, Andrew M. Davis, Tommaso Di Rocco, Wataru Fujiya, Ryota Fukai, Makiko K. Haba, Yuki Hibiya, Hiroshi Hidaka, Hisashi Homma, Peter Hoppe, Gary R. Huss, Kiyohiro Ichida, Tsuyoshi Iizuka, Trevor Ireland, Akira Ishikawa, Shoichi Itoh, Noriyuki Kawasaki, Noriko T. Kita, Koki Kitajima, Thorsten Kleine, Shintaro Komatani, Alexander N. Krot, Ming‐Chang Liu, Yuki Masuda, Mayu Morita, Kazuko Motomura, Frédéric Moynier, Izumi Nakai, Kazuhide Nagashima, Ann Nguyen, Larry Nittler, Morihiko Onose, Andreas Pack, Changkun Park, Laurette Piani, Liping Qin, Sara Russell, Naoya Sakamoto, Lauren Tafla, Haolan Tang, Kentaro Terada, Yasuko Terada, Tomohiro Usui, Sohei Wada, Meenakshi Wadhwa, Richard J. Walker, Katsuyuki Yamashita, Qing‐Zhu Yin, Shigekazu Yoneda, Edward D. Young, Hiroharu Yui, Ai‐Cheng Zhang, Tomoki Nakamura, Hiroshi Naraoka, Takaaki Noguchi, Ryuji Okazaki, Kanako Sakamoto, Hikaru Yabuta, Masanao Abe, Akiko Miyazaki, Aiko Nakato, Masahiro Nishimura, Tatsuaki Okada, Toru Yada, Kasumi Yogata, Satoru Nakazawa, Takanao Saiki, Satoshi Tanaka, Fuyuto Terui, Yuichi Tsuda, Sei‐ichiro Watanabe, Makoto Yoshikawa, Shogo Tachibana, Hisayoshi Yurimoto

    Meteoritics & Planetary Science    2024.11

    　View Summary

    Abstract

    Nucleosynthetic isotope variations are powerful tracers to determine genetic relationships between meteorites and planetary bodies. They can help to link material collected by space missions to known meteorite groups. The Hayabusa 2 mission returned samples from the Cb‐type asteroid (162173) Ryugu. The mineralogical, chemical, and isotopic characteristics of these samples show strong similarities to carbonaceous chondrites and in particular CI chondrites. The nucleosynthetic isotope compositions of Ryugu overlap with CI chondrites for several elements (e.g., Cr, Ti, Fe, and Zn). In contrast to these isotopes, which are of predominately supernovae origin, s‐process variations in Mo isotope data are similar to those of carbonaceous chondrites, but even more s‐process depleted. To further constrain the origin of this depletion and test whether this signature is also present for other s‐process elements, we report Zr isotope compositions for three bulk Ryugu samples (A0106, A0106‐A0107, C0108) collected from the Hayabusa 2 mission. The data are complemented with that of terrestrial rock reference materials, eucrites, and carbonaceous chondrites. The Ryugu samples are characterized by distinct 96Zr enrichment relative to Earth, indicative of a s‐process depletion. Such depletion is also observed for carbonaceous chondrites and eucrites, in line with previous Zr isotope work, but it is more extreme in Ryugu, as observed for Mo isotopes. Since s‐process Zr and Mo are coupled in mainstream SiC grains, these distinct s‐process variations might be due to SiC grain depletion in the analyzed materials, potentially caused by incomplete sample digestion, because the Ryugu samples were dissolved on a hotplate only to avoid high blank levels for other elements (e.g., Cr). However, local depletion of SiC grains cannot be excluded. An alternative, equally possible scenario is that aqueous alteration redistributed anomalous, s‐process‐depleted, Zr on a local scale, for example, into Ca‐phosphates or phyllosilicates.

    DOI

  • Nucleosynthetic s-Process Depletion in Mo from Ryugu samples returned by Hayabusa2

    N. Nakanishi, T. Yokoyama, A. Ishikawa, R.J. Walker, Y. Abe, J. Aléon, C.M.O'D. Alexander, S. Amari, Y. Amelin, K.-I. Bajo, M. Bizzarro, A. Bouvier, R.W. Carlson, M. Chaussidon, B.-G. Choi, N. Dauphas, A.M. Davis, T. Di Rocco, W. Fujiya, R. Fukai, I. Gautam, M.K. Haba, Y. Hibiya, H. Hidaka, H. Homma, P. Hoppe, G.R. Huss, K. Ichida, T. Iizuka, T.R. Ireland, S. Itoh, N. Kawasaki, N.T. Kita, K. Kitajima, T. Kleine, S. Komatani, A.N. Krot, M.-C. Liu, Y. Masuda, M. Morita, K. Motomura, F. Moynier, I. Nakai, K. Nagashima, A. Nguyen, L. Nittler, M. Onose, A. Pack, C. Park, L. Piani, L. Qin

    Geochemical Perspectives Letters    2023.12

    DOI

  • Dissipation of Tungsten-182 Anomalies in the Archean Upper Mantle: Evidence from the Black Hills, South Dakota, USA

    Nao Nakanishi, Igor S. Puchtel, Richard J. Walker, Peter I. Nabelek

    Chemical Geology    2023.02

    DOI

  • Geochemical constraints on the formation of chondrules: Implication from Os and Fe isotopes and HSE abundances in metals from CR chondrites

    Nao Nakanishi, Tetsuya Yokoyama, Satoki Okabayashi, Hikaru Iwamori, Takafumi Hirata

    Geochimica et Cosmochimica Acta    2022.02

    DOI

  • Tungsten-182 evidence for an ancient kimberlite source

    Nao Nakanishi, Andrea Giuliani, Richard Carlson, Mary Horan, Jon Woodhead, Graham Pearson, Richard Walker

    Proceedings of the National Academy of Sciences    2021.05

    　View Summary

    <jats:title>Significance</jats:title>
    <jats:p>
    Kimberlites are igneous rocks derived from deep mantle sources. Recent studies have suggested that certain kimberlites originated from a mantle source with relatively primitive chemical composition that was created by early Earth processes. We present W isotope data for a global suite of kimberlites with variable formation ages and find their mantle source(s) to be characterized by
    <jats:sup>182</jats:sup>
    W/
    <jats:sup>184</jats:sup>
    W averaging ∼6 ppm lower than the upper mantle ratio. This result is consistent with derivation of some kimberlites from one or more early formed mantle reservoirs. The low
    <jats:sup>182</jats:sup>
    W/
    <jats:sup>184</jats:sup>
    W of these kimberlites is indicative of an ancient mantle source modified by some form of core–mantle interaction, an early silicate fractionation event, an overabundance of late-accreted materials, or a combination of these.
    </jats:p>

    DOI

  • Refinement of the Micro‐Distillation Technique for Isotopic Analysis of Geological Samples with pg‐Level Osmium Contents

    Nao Nakanishi, Tetsuya Yokoyama, Akira Ishikawa

    Geostandards and Geoanalytical Research    2019.06

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    <jats:p>In recent years, the <jats:sup>187</jats:sup>Re–<jats:sup>187</jats:sup>Os isotope system has been increasingly used to study samples containing very small quantities of Os. For such samples, optimisation of measurement procedures is essential to minimise the loss of Os before mass spectrometric measurements. Micro‐distillation is a necessary purification step that is applied after the main Os chemical separation procedure, prior to Os isotope ratio measurements by negative‐thermal ionisation mass spectrometry (N‐<jats:styled-content style="fixed-case">TIMS</jats:styled-content>). However, unlike the other separation steps, this procedure has not yet been optimised for small samples. In this study, we present a refined micro‐distillation method that achieved higher yields and allowed high‐precision R(<jats:sup>187</jats:sup>Os/<jats:sup>188</jats:sup>Os) expressed as <jats:sup>187</jats:sup>Os/<jats:sup>188</jats:sup>Os measurements for small‐sized geological samples that contain only a few pg Os. The Os recovery in the micro‐distillation step was tested by changing the operating conditions including heating time and temperature, and amounts of oxidant and reductant. Recoveries were measured by the isotope dilution <jats:styled-content style="fixed-case">ICP</jats:styled-content>‐<jats:styled-content style="fixed-case">MS</jats:styled-content> method after the addition of <jats:sup>190</jats:sup>Os‐enriched spike solution. We found that the most critical factor controlling the chemical yield of Os during micro‐distillation is the extent of dilution of the reductant (<jats:styled-content style="fixed-case">HB</jats:styled-content>r) by H<jats:sub>2</jats:sub>O evaporated from the oxidant. A refined micro‐distillation method, in which the amount of oxidant solution is reduced from the conventional method, achieved an improved chemical yield of Os (~ 90%). This refined method was applied to the measurement of <jats:sup>187</jats:sup>Os/<jats:sup>188</jats:sup>Os by N‐<jats:styled-content style="fixed-case">TIMS</jats:styled-content> of varying test portions of the geological reference material <jats:styled-content style="fixed-case">BIR</jats:styled-content>‐1a. The resulting <jats:sup>187</jats:sup>Os/<jats:sup>188</jats:sup>Os ratios of <jats:styled-content style="fixed-case">BIR</jats:styled-content>‐1a matched the literature data, with propagated uncertainties of 0.2, 1.1 and 11% digested sample quantities containing 150, 10 and 1 pg of Os, respectively.</jats:p>

    DOI

  • Fractionation of highly siderophile elements in metal grains from unequilibrated ordinary chondrites: Implications for the origin of chondritic metals

    Satoki Okabayashi, Tetsuya Yokoyama, Nao Nakanishi, Hikaru Iwamori

    Geochimica et Cosmochimica Acta   244   197 - 215  2019.01

    DOI

  • Re‐Os isotope systematics and fractionation of siderophile elements in metal phases from <scp>CB</scp>a chondrites

    Nao Nakanishi, Tetsuya Yokoyama, Satoki Okabayashi, Tomohiro Usui, Hikaru Iwamori

    Meteoritics &amp; Planetary Science    2018.05

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    <jats:title>Abstract</jats:title><jats:p>We report Os isotope compositions of metal grains in two <jats:styled-content style="fixed-case">CB</jats:styled-content><jats:sub>a</jats:sub> chondrites (Bencubbin and Gujba) determined using a micromilling sampling coupled with thermal ionization mass spectrometry, together with the abundances of major and trace siderophile elements obtained by electron probe microanalysis and femtosecond laser ablation inductively coupled plasma–mass spectrometry. The <jats:styled-content style="fixed-case">CB</jats:styled-content><jats:sub>a</jats:sub> metal grains presented <jats:sup>187</jats:sup>Os/<jats:sup>188</jats:sup>Os ratios akin to carbonaceous chondrites with limited variations (0.1257–0.1270). Most of the <jats:styled-content style="fixed-case">CB</jats:styled-content><jats:sub>a</jats:sub> metal grains were scattered along a <jats:sup>187</jats:sup>Re‐<jats:sup>187</jats:sup>Os reference isochron of <jats:styled-content style="fixed-case">IIIAB</jats:styled-content> iron meteorites, indicating that the <jats:styled-content style="fixed-case">CB</jats:styled-content><jats:sub>a</jats:sub> metals experienced limited Re‐Os fractionation at the time of their formation. The Re/Os ratios of sampling spots for the <jats:styled-content style="fixed-case">CB</jats:styled-content><jats:sub>a</jats:sub> metals, recast from the observed <jats:sup>187</jats:sup>Os/<jats:sup>188</jats:sup>Os ratios, had a positive correlation with their Os/Ir ratios. In addition, the metal grains showed a positive correlation in a Pd/Fe versus Ni/Fe diagram. These correlations suggest that the <jats:styled-content style="fixed-case">CB</jats:styled-content><jats:sub>a</jats:sub> metal grains have formed via equilibrium condensation or evaporation from a gaseous reservoir at ~10<jats:sup>−4</jats:sup> bar with enhanced metal abundances. Compared to the Bencubbin metals, the Gujba metals are characterized by having systematically lower Pd/Fe and Ni/Fe ratios that span subchondritic values. Such a difference was most likely induced by the compositionally heterogeneous impact plume from which the metals were condensed.</jats:p>

    DOI

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Syllabus

 

Internal Special Research Projects

  • ベスタ隕石及びメソシデライト隕石の同位体組成からみる天体ベスタのコアマントル分離

    2023  

    　View Summary

    ベスタ隕石及びメソシデライト隕石の元素・同位体分析により、その起源と進化を議論する事を最終目標に今年度はタングステン同位体分析法の確立を目指した。分析は（１）試料分解とイオン交換樹脂を用いたタングステンの分離工程と（２）表面電離型質量分析装置を用いたタングステン同位体測定工程に大別できる。これらの工程でタングステンが高回収率で分離され、精度よく同位体比が測定されることをタングステン標準溶液、鉄隕石試料を用いてテストした。その結果、（１）の化学処理工程においては、数種類の分離方法を試し、メソシデライト隕石のような鉄ニッケルが多く含まれる試料の場合、陽イオン交換樹脂と陰イオン交換樹脂を組み合わせることでタングステンが効率的に分離できることがわかった。（２）の装置分析の工程ではタングステン測定に最適な装置設定を検討した上で、測定に用いるフィラメント、アクチベータの種類を変えながらタングステンビーム強度が一番高く出るための条件を比較した。その結果、タングステン標準溶液を用いた測定で182W/184W同位体比の繰り返し再現性~5 ppm(2SD)を達成する事が出来た。これら結果を踏まえて、天然試料である化学処理工程を行った鉄隕石試料について測定を行ったところ、参考文献値と誤差の範囲で一致した182W/184W比を得ることができた。