研究者データベース

坂本 直哉(サカモト ナオヤ)
創成研究機構 研究部
助教

基本情報

所属

  • 創成研究機構 研究部

職名

  • 助教

学位

  • 博士(理学)(北海道大学)

ホームページURL

J-Global ID

研究キーワード

  • SIMS   隕石   同位体   質量分析   イメージセンサ   同位体イメージング   二次イオン質量分析計   宇宙化学   

研究分野

  • 自然科学一般 / 固体地球科学
  • ライフサイエンス / 分子生物学
  • 自然科学一般 / 宇宙惑星科学

職歴

  • 2007年10月 - 現在 北海道大学 創成研究機構 助教
  • 2007年04月 - 2007年09月 日本学術振興会 特別研究員 (DC2)

研究活動情報

論文

  • Ai-Cheng Zhang, Jie-Ya Li, Jia-Ni Chen, Yuan-Yun Wen, Yan-Jun Guo, Yang Li, Naoya Sakamoto, Hisayoshi Yurimoto
    GEOCHIMICA ET COSMOCHIMICA ACTA 329 38 - 50 2022年07月 
    Impact is a fundamental process shaping the formation and evolution of planets and asteroids. It is inevitable that some materials on the surface of planets and asteroids have been impacted for many times. However, unambiguous petrological records for multiple post-formation impact events are rarely described. Here, we report that the thin shock melt veins of the shocked eucrite Northwest Africa 8647 are dominated by a fine-grained intergranular or vermicular pigeonite and anorthite assemblage, rather than compact vacancy-rich clinopyroxene. Vacancy-rich clinopyroxene in the veins instead is ubiquitous as irregularly-shaped, relict grains surrounded by intergranular or vermicular pigeonite and anorthite assemblage. The silica fragments entrained in shock melt veins contain a coesite core and a quartz rim. The occurrences of vacancy-rich clinopyroxene and coesite can be best explained by two impact events. The first impact event produced the shock melt veins and lead to the formation of vacancy-rich clinopyroxene and coesite. The second impact event heated the fine-grained melt veins and lead to the widespread partial decomposition of vacancy-rich clinopyroxene and the partial back-transformation of coesite. This paper is the first report of the decomposition reaction of shock-induced vacancy-rich clinopyroxene in extraterrestrial materials. We propose that widespread decomposition and/or back-transformation of high-pressure minerals in shocked meteorites can be considered as important records of multiple impact events.(C) 2022 Elsevier Ltd. All rights reserved.
  • Charline Lormand, Georg Florian Zellmer, Naoya Sakamoto, Teresa Ubide, Geoff Kilgour, Hisayoshi Yurimoto, Alan Palmer, Karoly Németh, Yoshiyuki Iizuka, Anja Moebis
    Contributions to Mineralogy and Petrology 176 11 2021年11月 
    AbstractArc magmas typically contain phenocrysts with complex zoning and diverse growth histories. Microlites highlight the same level of intracrystalline variations but require nanoscale resolution which is globally less available. The southern Taupo Volcanic Zone (TVZ), New Zealand, has produced a wide range of explosive eruptions yielding glassy microlite-bearing tephras. Major oxide analyses and textural information reveal that microlite rims are commonly out of equilibrium with the surrounding glass. We mapped microlites and microcrysts at submicron resolution for major and trace element distributions and observed three plagioclase textural patterns: (1) resorption and overgrowth, (2) oscillatory zoning, and (3) normal (sharp) zoning. Pyroxene textures are diverse: (1) resorption and overgrowth, (2) calcium-rich bands, (3) hollow textures, (4) oscillatory zoning, (5) sector zoning, (6) normal zoning and (7) reverse zoning. Microlite chemistry and textures inform processes operating during pre-eruptive magma ascent. They indicate a plumbing system periodically intruded by short-lived sub-aphyric dykes that entrain microantecrysts grown under diverse physico-chemical conditions and stored in rapidly cooled, previously intruded dykes. Changes in temperature gradients between the intrusion and the host rock throughout ascent and repeated magma injections lead to fluctuations in cooling rates and generate local heterogeneities illustrated by the microlite textures and rim compositions. Late-stage degassing occurs at water saturation, forming thin calcic microcryst rims through local partitioning effects. This detailed investigation of textures cryptic to conventional imaging shows that a significant proportion of the micrometre-sized crystal cargo of the TVZ is of antecrystic origin and may not be attributed to late-stage nucleation and growth at the onset of volcanic eruptions, as typically presumed.
  • Noriyuki Kawasaki, Shoichi Itoh, Naoya Sakamoto, Steven B. Simon, Daiki Yamamoto, Hisayoshi Yurimoto
    METEORITICS & PLANETARY SCIENCE 56 6 1224 - 1239 2021年06月 
    Coarse-grained, igneous Ca-Al-rich inclusions (CAIs) in CV chondrites formed through multiple melting events. We conducted in situ O-isotope analysis and Al-Mg systematics by secondary ion mass spectrometry of relict and overgrown minerals from a partial melting event in an Allende Type B CAI, Golfball. Golfball has a Type B CAI bulk composition and a unique structure: a fassaite-rich mantle enclosing a melilite-rich core. Many of the blocky melilite crystals in the core have irregularly shaped, Al-rich (angstrom k(5-15)) cores enclosed in strongly zoned (angstrom k(30-70)) overgrowths. Since the Al-rich melilite grains could not have formed from a melt of Golfball, they are interpreted as relict grains that survived later melting events. The O-isotopic compositions of the blocky melilite crystals plot along the carbonaceous chondrite anhydrous mineral line, ranging between Delta O-17 similar to -14 parts per thousand and -5 parts per thousand. The Al-rich relict melilite grains and their overgrowths exhibit the same O-isotopic compositions, while the O-isotopic compositions are varied spatially among melilites. We found that the O-isotopic compositions steeply change across several melilite crystals within few tens of micrometers, indicating the O-isotopic compositions of the melt could not have been homogenized during the partial melting in that scale. According to the time scale of O self-diffusivity in the melt, the cooling rate of the partial melting event is calculated to be >6 x 10(4) K h(-1). Al-Mg isotope data for core minerals plot on a straight line on an Al-Mg evolution diagram. A mineral isochron for Golfball gives initial Al-26/Al-27 of (4.42 +/- 0.20) x 10(-5) and initial delta Mg-26* of -0.035 +/- 0.050 parts per thousand. The chemical and O-isotopic compositions of melilite and those initial values imply that its precursor consisted of fluffy Type A and/or fine-grained CAIs. The partial melting event for Golfball may have occurred in very short order after the precursor formation.
  • Wei Sun, Takashi Yoshino, Naoya Sakamoto, Hisayoshi Yurimoto
    Earth and Planetary Science Letters 561 116815 - 116815 2021年05月
  • Shoh Tagawa, Naoya Sakamoto, Kei Hirose, Shunpei Yokoo, John Hernlund, Yasuo Ohishi, Hisayoshi Yurimoto
    NATURE COMMUNICATIONS 12 1 2021年05月 
    Hydrogen is one of the possible alloying elements in the Earth's core, but its siderophile (iron-loving) nature is debated. Here we experimentally examined the partitioning of hydrogen between molten iron and silicate melt at 30-60 gigapascals and 3100-4600 kelvin. We find that hydrogen has a metal/silicate partition coefficient D-H >= 29 and is therefore strongly siderophile at conditions of core formation. Unless water was delivered only in the final stage of accretion, core formation scenarios suggest that 0.3-0.6 wt% H was incorporated into the core, leaving a relatively small residual H2O concentration in silicates. This amount of H explains 30-60% of the density deficit and sound velocity excess of the outer core relative to pure iron. Our results also suggest that hydrogen may be an important constituent in the metallic cores of any terrestrial planet or moon having a mass in excess of similar to 10% of the Earth.
  • Ai-Cheng Zhang, Qin-Ting Jiang, Naotaka Tomioka, Yan-Jun Guo, Jia-Ni Chen, Yang Li, Naoya Sakamoto, Hisayoshi Yurimoto
    GEOPHYSICAL RESEARCH LETTERS 48 5 2021年03月 
    Shock-lithification is a fundamental process of making rocks from fine-grained and porous regoliths on the surface of the Moon. Previous investigations have constrained potential shock pressures during shock-lithification based on experimental and numerical simulations. However, pressure and temperature conditions during shock-lithification have not been directly inferred from natural lunar breccias. Here, we report the discovery of widespread tissintite in strongly shock-lithified lunar meteorites, accompanied occasionally by Si-rich corundum and coesite. The coexistence of tissintite and coesite and the absence of stishovite in molten regions indicate a shock pressure of 4-8 GPa, which might be the pressure boundary between weak and strong shock-lithification. Meanwhile, the presence of Si-rich corundum imposes a temperature constraint of similar to 2,300 K for the intergranular melts. This temperature constraint has profound significance for interpreting the behaviors of volatile and moderately volatile elements and remanent magnetization records during strongly shock-lithification of lunar breccias.
  • Takayuki Nonoyama, Lei Wang, Masumi Tsuda, Yuki Suzuki, Ryuji Kiyama, Kazunori Yasuda, Shinya Tanaka, Kousuke Nagata, Ryosuke Fujita, Naoya Sakamoto, Noriyuki Kawasaki, Hisayoshi Yurimoto, Jian Ping Gong
    ADVANCED HEALTHCARE MATERIALS 10 3 2021年02月 
    Tough double network (DN) hydrogels are promising substitutes of soft supporting tissues such as cartilage and ligaments. For such applications, it is indispensable to robustly fix the hydrogels to bones with medically feasible methods. Recently, robustly bonding the DN hydrogels to defected bones of rabbits in vivo has been proved successful. The low crystalline hydroxyapatite (HAp) of calcium-phosphate-hydroxide salt coated on the surface layer of the DN hydrogels induced spontaneous osteogenesis penetrating into the semi-permeable hydrogels to form a gel/bone composite layer. In this work, the Ca-44 isotope-doped HAp/DN hydrogel is implanted in a defect of rabbit femoral bone and the dynamic osteogenesis process at the gel/bone interface is analyzed by tracing the calcium isotope ratio using isotope microscopy. The synthetic HAp hybridized on the surface layer of DN gel dissolves rapidly in the first two weeks by inflammation, and then the immature bone with a gradient structure starts to form in the gel region, reutilizing the dissolved Ca ions. These results reveal, for the first time, that synthetic HAp is reutilized for osteogenesis. These facts help to understand the lifetime of bone absorbable materials and to elucidate the mechanism of spontaneous, non-toxic, but strong fixation of hydrogels to bones.
  • Raimundo Brahm, Georg F. Zellmer, Takeshi Kuritani, Daniel Coulthard, Mitsuhiro Nakagawa, Naoya Sakamoto, Hisayoshi Yurimoto, Eiichi Sato
    FRONTIERS IN EARTH SCIENCE 8 2021年01月 
    Olivine-hosted melt inclusions (MIs) are widely used as a tool to study the early stages of magmatic evolution. There are a series of processes that affect MI compositions after trapping, including post-entrapment crystallization (PEC) of the host mineral at the MI boundaries, exsolution of volatile phases into a "shrinkage bubble" and diffusive exchange between a MI and its host. Classical correction schemes applied to olivine-hosted MIs include PEC correction through addition of olivine back to the melt until it reaches equilibrium with the host composition and "Fe-loss" correction due to Fe-Mg diffusive exchange. These corrections rely on the assumption that the original host composition is preserved. However, for many volcanic samples the crystal cargo is thought to be antecrystic, and the olivine composition may thus have been completely re-equilibrated during long crystal storage times. Here, we develop a novel MI correction scheme that is applicable when the original host crystal composition has not been preserved and the initial MI composition variability can be represented by simple fractional crystallization (FC). The new scheme allows correction of MI compositions in antecrystic hosts with long and varied temperature histories. The correction fits a set of MI compositions to modelled liquid lines of descent generated by FC. A MATLAB(R) script (called MushPEC) iterates FC simulations using the rhyolite-MELTS algorithm. In addition to obtaining the corrected MI compositions, the application of this methodology provides estimations of magmatic conditions during MI entrapment. A set of MIs hosted in olivine crystals of homogeneous composition (Fo(77-78)) from a basaltic tephra of Akita-Komagatake volcano was used to test the methodology. The tephra sample shows evidence of re-equilibration of the MIs to a narrow Mg# range equivalent to the carrier melt composition. The correction shows that olivine hosts were stored in the upper crust (c. 125 - 150 MPa) at undersaturated H2O contents of c. 1 - 2 wt% H2O).
  • Noriyuki Kawasaki, Changkun Park, Shigeyuki Wakaki, Hwayoung Kim, Sunyoung Park, Toshihiro Yoshimura, Kazuya Nagaishi, Hyun Na Kim, Naoya Sakamoto, Hisayoshi Yurimoto
    GEOCHEMICAL JOURNAL 55 4 283 - 287 2021年 
    Instrumental mass fractionation of Mg-isotopes and the relative sensitivity factor (RSF) for Al-27/Mg-24 ratios for in situ analysis by secondary ion mass spectrometry were investigated for minerals in Ca-Al-rich inclusions (CAIs) of meteorites, to verify systematic errors in Al-Mg chronological systematics of CAIs. We synthesized seventeen glasses with different chemical compositions that imitate those for CAI minerals and measured their Al-Mg isotopic compositions. In particular, the variation range of RSFs for six melilite glasses almost covering chemical compositions of CAI melilite is 2.0 +/- 0.3%, indicating that systematic error for Al-27/Mg-24 for melilite is less than 2.0 +/- 0.3% and likely corresponds to that of an Al-26-Mg-26 relative age of similar to 0.01 Myr for melilite-rich CAIs. Our data strongly support the robustness of variations in initial Al-26/Al-27 ratios among CAIs, corresponding to a formation age spread of similar to 0.4 Myr at the very beginning of the Solar System formation.
  • Jie-Ya Li, Ai-Cheng Zhang, Naoya Sakamoto, Hisayoshi Yurimoto, Li-Xin Gu
    AMERICAN MINERALOGIST 105 11 1656 - 1661 2020年11月 
    The diversity of lithologies is an important proxy of internal evolution in differentiated planets and asteroids. The major lithologies in Vesta, based on the howardite-eucrite-diogenite clan meteorites, include basalt, gabbro, noritic orthopyroxenite, orthopyroxenite, dunite, harzburgite, and dacite. No other lithology has been reported up to date. In this study, we report a new occurrence of corundum in eucrite meteorite Northwest Africa (NWA) 8647. Three-dimensional petrographic observations reveal that the corundum grain occurs as a mineral inclusion in a highly deformed pyroxene fragment. The texture indicates that the corundum is not a contaminant. The corundum-associated pyroxenes have Fe-Mn compositions consistent with typical pyroxenes from howardite-eucrite-diogenite meteorites. We suggest that the corundum grain could be a xenocryst incorporated during the ascent of a basaltic magma. The results might indicate the presence of an Al-rich, Si-poor region, probably lithology in the interior of Vesta, implying that the evolution and internal structure should be much more complex than previously thought.
  • C. Lormand, G. F. Zellmer, G. N. Kilgour, K. Németh, A. S. Palmer, N. Sakamoto, H. Yurimoto, T. Kuritani, Y. Iizuka, A. Moebis
    Journal of Petrology 61 10 2020年10月01日 
    To assess whether magma ascent rates control the style of volcanic eruption, we have studied the petrography, geochemistry and size distribution of microlites of plagioclase and pyroxene from historical eruptions from Tongariro, Ruapehu and Ngauruhoe volcanoes located in the southern Taupo Volcanic Zone, New Zealand. The studied deposits represent glassy andesitic and dacitic tephra shards from the Mangamate, Mangatawai, Tufa Trig and Ngauruhoe tephra formations, ranging in age from 11 000 years bp to ad 1996. Covering a range in eruption styles and sizes from Strombolian to Plinian, these samples provide an excellent opportunity to explore fundamental volcanic processes such as pre-eruptive magma ascent processes. Our quantitative petrographic analysis shows that larger microlites (>30 μm) display complex growth zoning, and only the smallest crystals (<30 μm) have formed during magma ascent in the conduit. Using a combination of orthopyroxene geothermometry, plagioclase hygrometry, and MELTS modelling, we show that these microlites nucleated at maximum pressures of 550 MPa (c. 16·5 km) from hot andesitic magmas (1010-1130 °C) with low H2O content (0-1·5 wt%). Size distributions of a total of >60 000 microlites, involving 22 tephras and 99 glass shards, yield concave-up curves, and the slopes of the pyroxene microlite size distributions, in combination with well-constrained orthopyroxene crystal growth rates from one studied tephra, indicate microlite population growth times of ∼3 ± 1 days, irrespective of eruption style. These data imply that microlites form in response to cooling of melts ascending at velocities of <5 cm s-1 prior to H2O exsolution, which occurs only at <33 MPa. Maximum magma ascent rates in the upper conduit, calculated using the exsolution of water during final decompression, range between 3 and 12 m s-1; that is, at least an order of magnitude lower than the hypersonic vent velocities typical of Vulcanian or sub-Plinian eruptions (up to 400 m s-1). This implies that magma ascent from depths of an average of 4 km occurs in dykes, and that vent velocities at the surface are controlled by a reduction of conduit cross-section towards the surface (e.g. dyke changing to cylindrical conduit).
  • Yong Xiong, Ai-Cheng Zhang, Noriyuki Kawasaki, Chi Ma, Naoya Sakamoto, Jia-Ni Chen, Li-Xin Gu, Hisayoshi Yurimoto
    METEORITICS & PLANETARY SCIENCE 55 10 2184 - 2205 2020年10月 
    Calcium-aluminum-rich inclusions (CAIs) are the first solid materials formed in the solar nebula. Among them, ultrarefractory inclusions are very rare. In this study, we report on the mineralogical features and oxygen isotopic compositions of minerals in a new ultrarefractory inclusion CAI 007 from the CV3 chondrite Northwest Africa (NWA) 3118. The CAI 007 inclusion is porous and has a layered (core-mantle-rim) texture. The core is dominant in area and mainly consists of Y-rich perovskite and Zr-rich davisite, with minor refractory metal nuggets, Zr,Sc-rich oxide minerals (calzirtite and tazheranite), and Fe-rich spinel. The calzirtite and tazheranite are closely intergrown, probably derived from a precursor phase due to thermal metamorphism on the parent body. The refractory metal nuggets either exhibit thin exsolution lamellae of Fe,Ni-dominant alloy in Os,Ir-dominant alloy or are composed of Os,Ir,Ru,Fe-alloy and Fe,Ni,Ir-alloy with troilite, scheelite, gypsum, and molybdenite. The later four phases are apparently secondary minerals. The Zr,Sc,Y-rich core is surrounded by a discontinuous layer of closely intergrown hibonite and spinel. The CAIs are rimmed by Fe-rich spinel and Al-rich diopside. Perovskite has high concentrations of the most refractory rare earth elements (REEs) but is relatively depleted in the moderately refractory and volatile REEs, consistent with the ultrarefractory REE pattern. Based on this unusual Zr,Sc,Y-rich mineral assemblage, the layered distribution in CAI 007, and the REE concentrations in perovskite, we suggest that CAI 007 is an ultrarefractory inclusion of condensation origin. In CAI 007, hibonite, spinel, and probably Al-rich diopside are(16)O-rich (Delta O-17 similar to-22 parts per thousand) whereas perovskite and davisite are O-16-poor (Delta O-17 similar to-3 parts per thousand). Such oxygen isotope heterogeneity suggests that the UR inclusion formed in the various degrees of(16)O-rich nebular setting or was originally O-16-rich and then experienced oxygen isotope exchange with(16)O-poor fluid on the CV3 chondrite parent body.
  • Ai-Cheng Zhang, Run-Lian Pang, Naoya Sakamoto, Hisayoshi Yurimoto
    AMERICAN MINERALOGIST 105 7 1021 - 1029 2020年07月 [査読有り][通常論文]
     
    "Cr-Zr-Ca armalcolite" is a mineral originally found in Apollo samples five decades ago. However, no structural information has been obtained for this mineral. In this study, we report a new occurrence of "Cr-Zr-Ca armalcolite" and its associated mineral assemblage in an Mg-suite lithic clast (Clast-20) from the brecciated lunar meteorite Northwest Africa 8182. In this lithic clast, plagioclase (An = 88-91), pyroxene (Mg#[Mg/(Mg+Fe)] = 0.87-0.91) and olivine (Mg# = 0.86-0.87) are the major rock-forming minerals. Armalcolite and "Cr-Zr-Ca armalcolite" are observed with other minor phases including ilmenite, chromite, rutile, fluorapatite, merrillite, monazite, FeNi metal, and Fe-sulfide. Based on 38 oxygen atoms, the chemical formula of "Cr-Zr-Ca armalcolite" is (Ca0.99Na0.01)S-1.00(Ti14.22Fe2.06Cr2.01 Mg1.20Zr0.54Al0.49Ca0.21Y0.05Mn0.04Ce0.03Si0.03La0.01Nd0.01Dy0.01)S20.91O38. Electron backscatter diffraction (EBSD) results reveal that the "Cr-Zr-Ca armalcolite" has a loveringite R (3) over bar structure, differing from the armalcolite Bbmm structure. The estimated hexagonal cell parameters a and c of "Cr-Zr-Ca armalcolite" are 10.55 and 20.85 angstrom, respectively. These structural and compositional features indicate that "Cr-Zr-Ca armalcolite" is loveringite, not belonging to the armalcolite family. Comparison with "Cr-Zr-Ca armalcolite" and loveringite of other occurrences implies that loveringite might be an important carrier of rare earth elements in lunar Mg-suite rocks. The compositional features of plagioclase and mafic silicate minerals in Clast-20 differ from those in other Mg-suite lithic clasts from Apollo samples and lunar meteorites, indicating that Clast-20 represents a new example of diverse lunar Mg-suite lithic clasts.
  • Noriyuki Kawasaki, Sohei Wada, Changkun Park, Naoya Sakamoto, Hisayoshi Yurimoto
    Geochimica et Cosmochimica Acta 279 1 - 15 2020年06月15日 [査読有り][通常論文]
     
    © 2020 Elsevier Ltd Fine-grained Ca-Al-rich inclusions (FGIs) in CV chondrites are suggested to be condensates formed directly from the solar nebular gas. Al–Mg mineral isochrons of seven FGIs from reduced CV chondrites Efremovka, Vigarano, Thiel Mountains 07007, and Northwest Africa 8613 were obtained via in situ Al–Mg isotope measurements using secondary ion mass spectrometry. The slopes of the mineral isochrons for seven FGIs exhibit statistically significant variations in initial 26Al/27Al ratios, (26Al/27Al)0, ranging from (5.19 ± 0.17) to (3.35 ± 0.21) × 10−5, which correspond to a relative age spread of 0.44 ± 0.07 Myr. Inferred upper limit of (26Al/27Al)0 for the FGIs is identical to the Solar System (26Al/27Al)0 of ∼5.2 × 10−5 as determined by whole-rock Al–Mg isochron studies for CAIs in CV chondrites. The intercepts of the mineral isochrons, the initial 26Mg/24Mg ratios the FGIs formed with, are consistent with Mg-isotope evolution path of a solar-composition nebular gas. The observed variations in (26Al/27Al)0 for FGIs are essentially similar to those (∼5.2 to ∼4.2 × 10−5) for coarse-grained, igneous CAIs of CV chondrites that are formed by melting and solidification. If 26Al was distributed homogeneously in the forming region, then our data indicate that thermal processes of condensation and melting for CAI formation occurred contemporaneously and continued for at least ∼0.4 Myr at the very beginning of the Solar System. Alternatively, the observed variations in (26Al/27Al)0 also indicate the possibility of heterogeneous distributions of 26Al in the forming region, corresponding to a range of over at least 3.4 × 10–5 < (26Al/27Al)0 < 5.2 × 10–5.
  • Ai-Cheng Zhang, Noriyuki Kawasaki, Minami Kuroda, Yang Li, Hua-Pei Wang, Xue-Ning Bai, Naoya Sakamoto, Qing-Zhu Yin, Hisayoshi Yurimoto
    GEOCHIMICA ET COSMOCHIMICA ACTA 275 48 - 63 2020年04月 [査読有り][通常論文]
     
    Most meteorites are believed to be chips from planetesimals and can provide clues to constrain the chemical evolution and dynamic history of the early Solar System. In this study, we report two unique fragments (ALF-1 and ALF-2) enclosed in the CH3 carbonaceous chondrite Sayh al Uhaymir 290. These two fragments are dominated by Ca,Fe-rich olivine with various amounts of Al,Ti-rich augite, anorthite, oxide minerals, Ca-phosphate mineral, FeNi metal, enstatite, and less Al,Ti-rich augite. The Ca-Mg-Fe systematics and Fe/Mn ratios of olivine grains in the two fragments are similar to that of the volcanic angrites. These similar features imply that the parent body of the two fragments might have bulk chemistry, oxygen fugacity, and differentiation resembling the angrite parent body. However, high-precision SIMS measurements reveal oxygen isotope compositions Delta O-17 = 0.91 +/- 0.18 parts per thousand (2 sigma) of olivine in the two fragments are distinctly different from that of known angrite meteorites, possibly representing a new type of basaltic planetesimal.The two fragments also have a few mineralogical features distinct from angrite meteorites. They include: (1) the lack of a typical igneous texture; (2) the coexistence of two spatially associated Al,Ti-rich augites with different contents of CaO, Al2O3, MgO, and P2O5; (3) the presence of an enstatite-dominant rim in ALF-1; (4) the presence of a Cr,Mn-rich margin in ALF-1; and (5) complex microscale heterogeneity in oxide minerals. We argue that these features could be due to complex thermal histories in their parent body and/or after ejection from their parent body. Among these features, the Mn,Cr-rich margin and the enstatite-dominant rim in ALF-1 can be best explained with thermal events in nebular settings. This implies that the differentiation of the parent body of the two fragments might have taken place prior to the dissipation of the nebular gas. (C) 2020 Elsevier Ltd. All rights reserved.
  • Ai-Cheng Zhang, Noriyuki Kawasaki, Huiming Bao, Jia Liu, Liping Qin, Minami Kuroda, Jian-Feng Gao, Li-Hui Chen, Ye He, Naoya Sakamoto, Hisayoshi Yurimoto
    NATURE COMMUNICATIONS 11 1 2020年03月 [査読有り][通常論文]
     
    Diogenites are a group of meteorites that are derived from the interior of the largest protoplanet Vesta. They provide a unique opportunity to understanding together the internal structure and dynamic evolution of this protoplanet. Northwest Africa (NWA) 8321 was suggested to be an unbrecciated noritic diogenite meteorite, which is confirmed by our oxygen and chromium isotopic data. Here, we find that olivine in this sample has been partly replaced by orthopyroxene, troilite, and minor metal. The replacement texture of olivine is unambiguous evidence of sulfur-involved metasomatism in the interior of Vesta. The presence of such replacement texture suggests that in NWA 8321, the olivine should be of xenolith origin while the noritic diogenite was derived from partial melting of pre-existing rocks and had crystallized in the interior of Vesta. The post-Rheasilvia craters in the north-polar region on Vesta could be the potential source for NWA 8321.
  • Nozomi Matsuda, Naoya Sakamoto, Shogo Tachibana, Hisayoshi Yurimoto
    Chemie der Erde 79 4 2019年12月 [査読有り][通常論文]
     
    © 2019 Due to their common occurrence in various types of chondrites, igneous rims formed on pre-existing chondrules throughout chondrule-forming regions of the solar nebula. Although the peak temperatures are thought to reach similar values to those achieved during chondrule formation events, the heating duration in chondrule rim formation has not been well defined. We determined the two-dimensional chemical and oxygen isotopic distributions in an igneous rim of a chondrule within the Northwest Africa 3118 CV3oxA chondrite with sub-micrometer resolution using secondary ion mass spectrometry and scanning electron microscopy. The igneous rim experienced aqueous alteration on the CV parent body. The aqueous alteration resulted in precipitation of the secondary FeO-rich olivine (Fa40–49) and slightly disturbed the Fe-Mg distribution in the MgO-rich olivine phenocrysts (Fa11–22) at about a 1 μm scale. However, no oxygen isotopic disturbances were observed at a scale greater than 100 nm. The MgO-rich olivine, a primary phase of igneous rim formation, has δ17O = −6 ± 3‰ and δ18O = −1 ± 4‰, and some grains contain extreme 16O-rich areas (δ17O, δ18O = ∼−30‰) nearly 10 μm across. We detected oxygen isotopic migration of approximately 1 μm at the boundaries of the extreme 16O-rich areas. Using oxygen self-diffusivity in olivine, the heating time of the igneous rim formation could have continued from several hours to several days at near liquidus temperatures (∼2000 K) in the solar nebula suggesting that the rim formed by a similar flash heating event that formed the chondrules.
  • Takeda Tomoya, Doiyama Sota, Azumi Junya, Shimada Yasuhiro, Tokuji Yoshihiko, Yamaguchi Hiroaki, Nagata Kosuke, Sakamoto Naoya, Aso Hisashi, Nakamura Takashi
    SCIENTIFIC REPORTS 9 1 13637 - 13637 2019年09月20日 [査読有り][通常論文]
     
    Reactive oxygen species (ROS) are very harmful to dermal cells, and it is thus important to develop cosmetics that protect the skin from ROS and other stimuli. Repagermanium is a synthetic water-soluble organogermanium polymer, and in this study, we attempted to visualize the incorporation of germanium into normal human dermal fibroblasts (NHDFs) using isotope microscopy. In addition, the content of 3-(trihydroxygermyl)propanoic acid (THGP), a hydrolyzed monomer of repagermanium, in NHDFs was determined through liquid chromatography mass spectrometry (LC-MS/MS), and the dose-dependent incorporation of THGP was confirmed. We then evaluated the preventive effects of THGP against ROS-induced NHDF death and confirmed the observed preventive effects through gene profiling and expression analysis. The addition of 0.59-5.9 mM THGP reduced cell death resulting from ROS damage caused by the reaction between xanthine oxidase and hypoxanthine and the direct addition of H2O2. Furthermore, this study provides the first demonstration that the effect of THGP was not due to the direct scavenging of ROS, which indicates that the mechanism of THGP differs from that of general antioxidants, such as ascorbic acid. The gene profiling and expression analysis showed that THGP suppressed the expression of the nuclear receptor subfamily 4 group A member 2 (NR4A2) gene, which is related to cell death, and the interleukin 6 (IL6) and chemokine (C-X-C motif) ligand 2 (CXCL2) genes, which are related to the inflammatory response. Furthermore, the production of IL6 induced by H2O2 was suppressed by the THGP treatment. Our data suggest that the preventive effect of THGP against ROS-induced cell death is not due to antioxidant enzymes or ROS scavenging.
  • Jean Bollard, Noriyuki Kawasaki, N. Sakamoto, Mia Olsen, Shoichi Itoh, Kirsten Larsen, Daniel Wielandt, Martin Schiller, James N. Connelly, Hisayoshi Yurimoto, Martin Bizzarro
    Geochimica et Cosmochimica Acta 260 62 - 83 2019年09月01日 [査読有り][通常論文]
     
    © 2019 The Authors Chondrites are fragments of asteroids that avoided melting and, thus, provide a record of the material that accreted to form protoplanets. The dominant constituent of chondrites are millimeter-sized chondrules formed by transient heating events in the protoplanetary disk. Some chondritic components, including chondrules, contain evidence of the extinct short-lived radionuclide 26Al (half-life of 0.73 Myr). The decay of 26Al is postulated to have been an important heat source promoting asteroidal melting and differentiation. Thus, understanding the 26Al inventory in the accretion regions of differentiated asteroids is critical to constrain the accretion timescales of protoplanets. The current paradigm asserts that the canonical 26Al/27Al ratio of ∼ 5 × 10−5 recorded by the oldest dated solids, calcium-aluminium refractory inclusions, represents that of the bulk Solar System. We report, for the first time, the 26Al-26Mg systematics of chondrules from the North West Africa (NWA) 5697 L 3.10 ordinary chondrite and Allende CV3OxA (Vigarano type) carbonaceous chondrite that have been previously dated by U-corrected Pb-Pb dating. Eight chondrules, which record absolute ages ranging from 4567.57 ± 0.56 to 4565.84 ± 0.72 Ma, define statistically-significant internal isochron relationships corresponding to initial (26Al/27Al) ([26Al/27Al]0) ratios in their precursors at the time of CAI formation at 4567.3 ± 0.16 Ma ranging from (3.92+4.53-2.95) × 10−6 to (2.74+1.30-1.09) × 10−5. These initial ratios are much lower than those predicted by the Pb-Pb ages, corresponding to age mismatches between the Pb-Pb and 26Al-26Mg systems ranging from 0.69+0.54-0.44 to 2.71+0.66-0.59 Myr. All chondrules record 54Cr/52Cr compositions indicating an origin from inner Solar System precursor material and, as such, we interpret the age mismatch to reflect a reduced initial abundance of 26Al in the chondrule precursors, similar to that proposed for the angrite parent body. In particular, the range of [26Al/27Al]0 ratios essentially defines two groups, which are apparently correlated with the absolute ages of the chondrules. A first group, charactertized by chondrules with absolute Pb-Pb ages identical to CAIs, defines a mean [26Al/27Al]0 value of (4.75+1.99-1.21) × 10−6, whereas a second group, with absolute ages ∼1 Myr younger than CAIs, record a mean mean [26Al/27Al]0 of (1.82+0.57-0.40) × 10−5. We interpret this systematic variability in [26Al/27Al]0 values as reflecting progressive inward transport and admixing of dust of solar composition and 26Al content from the outer disk during chondrule recycling and remelting. Finally, a reduced [26Al/27Al]0 ratio in chondrule precursors impacts our understanding of the accretion timescales of differentiated planetesimals if chondrules are indeed representative of inner disk material. Using the average [26Al/27Al]0 ratio of (1.36 ± 0.72) × 10−5 defined by the eight chondrules, thermal modelling constrains the accretion of differentiated planetesimals formed with this 26Al inventory from ∼0.1 to ∼0.9 Myr after Solar System formation to ensure melting by 26Al decay.
  • Zhang A. C, Kawasaki N, Kuroda M, Li Y, Wang H, Bai X. N, Sakamoto N, Yin Q. Z, Yurimoto H
    METEORITICS & PLANETARY SCIENCE 54 2019年08月 [査読有り][通常論文]
  • Isono Y, Sakamoto N, Ishibashi A, Song J, Yurimoto H
    METEORITICS & PLANETARY SCIENCE 54 2019年08月 [査読有り][通常論文]
  • Park C, Sakamoto N, Wakaki S, Kobayashi S, Kawasaki N, Yurimoto H
    METEORITICS & PLANETARY SCIENCE 54 2019年08月 [査読有り][通常論文]
  • Sakamoto N, Kawasaki N
    METEORITICS & PLANETARY SCIENCE 54 2019年08月 [査読有り][通常論文]
  • Matsuda N, Sakamoto N, Tachibana S, Yurimoto H
    METEORITICS & PLANETARY SCIENCE 54 2019年08月 [査読有り][通常論文]
  • Kawasaki N, Park C, Sakamoto N, Yurimoto H
    METEORITICS & PLANETARY SCIENCE 54 2019年08月 [査読有り][通常論文]
  • Wei Sun, Takashi Yoshino, Minami Kuroda, Naoya Sakamoto, Hisayoshi Yurimoto
    Journal of Geophysical Research: Solid Earth 124 6 5696 - 5707 2019年06月 [査読有り][通常論文]
     
    ©2019. American Geophysical Union. All Rights Reserved. Knowledge of water content and distribution in the Earth's mantle is critical to understanding the geochemical evolution and geodynamic processes of the Earth, since water can incorporate into nominally anhydrous minerals at high pressure and dramatically affect the chemical and physical properties of mantle minerals. Hydrogen diffusion controls the transport of water and electrical conductivity in the deep Earth but is not fully understood for olivine, the most abundant mineral in the upper mantle. Here we present new hydrogen self-diffusion coefficients determined from interdiffusion in H- and D-doped olivine single-crystal couples at the upper mantle conditions (3–13 GPa and 1,000–1,300 K). Present activation enthalpy for hydrogen migration is significant smaller than previous work determined within a limited measured temperature range. Parallel interdiffusion experiments with diversified water concentrations demonstrated that hydrogen diffusivity strongly accelerated by the water content in olivine. The geometric average diffusion coefficient on olivine is showed as a function of temperature and water content: (Formula presented.). Combined with the Nernst-Einstein relation, the present results can constrain the contribution of water to the electrical conductivity on olivine. It suggests that in situ conductivity measurements on hydrous olivine at low temperatures (<1,000 K) produced too low activation enthalpy to extrapolate to the higher temperatures. Comparison with previous results by conductivity measurements on single-crystal olivine suggests that the literature data except for Dai and Karato (2014) might overestimate water effect on conductivity because of heterogeneity of synthetic single crystals. Because of a change of dominant hydrogen diffusion mechanism at high temperature, this study suggests that the modeling of mantle conductivity with a high activation enthalpy from diffusion data is more trustworthy. Considering a reevaluated activation enthalpy on hydrogen diffusion and water solubility in olivine, comparisons between present conductivity model and geophysical observations suggest that hydration of olivine cannot account for extremely high conductive values (10−2–10−1 S/m) observed in the oceanic asthenosphere.
  • May Sas, Noriyuki Kawasaki, Naoya Sakamoto, Phil Shane, Georg F. Zellmer, Adam J.R. Kent, Hisayoshi Yurimoto
    Chemical Geology 513 153 - 166 2019年05月20日 [査読有り][通常論文]
     
    © 2019 Elsevier B.V. We investigated the potential of multi-collector secondary ion mass spectrometry (MC-SIMS) as a tool for obtaining Sr isotopic compositions in plagioclase, a ubiquitous mineral in igneous rocks that serves as a recorder of crystallization history. MC-SIMS allows for high spatial resolution analysis (~12 μm in this study) of isotopes, and therefore improves the temporal scale at which fluctuations in crystallization conditions can be recognized, ultimately improving our understanding of rates of magmatic processes. Plagioclase crystals from two young rhyolitic deposits from two major eruptive complexes, Tarawera and Haroharo, of the Okataina Volcanic Centre in New Zealand were analysed. Results were corrected for matrix effects using linear modelling of MC-SIMS data versus An contents, as well as 87 Sr/ 86 Sr ratios acquired via laser ablation inductively-coupled plasma mass spectrometry (LA-MC-ICP-MS). Corrected MC-SIMS Sr isotopic ratios had an average 2σ uncertainty of ±0.0008 per spot, and were homogeneous in Okataina plagioclase at high spatial resolutions. Average LA-MC-ICP-MS 87 Sr/ 86 Sr ratios of plagioclase from both intra-caldera volcanic complexes (Tarawera 87 Sr/ 86 Sr = 0.7056 and Haroharo 87 Sr/ 86 Sr = 0.7054) suggest similar magma sources and similar assimilation and fractional crystallization processes for the two complexes. Overall homogeneity of plagioclase (excluding relict cores) indicates no significant changes in contributions (i.e., crustal assimilation, mafic influx) to the system during the majority of plagioclase crystal growth. Furthermore, lack of 87 Sr/ 86 Sr ratio fluctuations in plagioclase rims suggest interaction between the resident silicic magma and the intruding mafic magma that triggered the eruptions was largely limited to volatile and heat transfer. Using appropriate standards and analysis, this MC-SIMS method can be used to detect short-lived, open-system events in magma reservoirs where differences in 87 Sr/ 86 Sr isotopic ratios are significant.
  • Takashi Yoshizaki, Daisuke Nakashima, Tomoki Nakamura, Changkun Park, Naoya Sakamoto, Hatsumi Ishida, Shoichi Itoh
    GEOCHIMICA ET COSMOCHIMICA ACTA 252 39 - 60 2019年05月 [査読有り][通常論文]
     
    Ultrarefractory (UR) phases in calcium-aluminum-rich inclusions (CAIs) could have formed at higher temperature compared to common CAI minerals and thus they potentially provide constraints on very high temperature processes in the solar nebula. We report a detailed characterization of the mineralogy, petrology and oxygen isotopic composition of an UR phase davisite (CaScAlSiO6) bearing CAI from a reduced type CV chondrite. The CAI is an irregular-shaped, compound inclusion that consists of five units that are composed of melilite + spinel + Al, Ti-rich pyroxene +/- perovskite with various modal abundances of minerals and lithologies, and surrounded by the Wark-Lovering (WL) rim. Davisite occurs only in one lithological unit that consists of three chemically and isotopically distinct parts: (i) O-16-poor (-20 parts per thousand <= delta O-18 <= 0 parts per thousand) regions with reversely-zoned melilite and davisite; (ii) O-16-rich (-50 parts per thousand <= delta O-18 <= -40 parts per thousand) regions consisting of unzoned, gehlenitic melilite, Al, Ti-rich diopside and spinel; and (iii) spinel framboids composed of O-16-rich spinel and O-16-poor melilite. Absence of secondary iron- and/or alkali-rich phases, occurrence of low-iron, manganese-enriched (LIME) olivine, and random distribution of the oxygen isotopic heterogeneity indicate that primitive chemical and isotopic compositions are preserved in the inclusion. The occurrence of chemical and isotopic heterogeneities with sharp boundaries in the CAI indicates formation of the inclusion by an aggregation of mineral assemblages formed and processed separately at different time and/or space in the solar nebula. Although isotope exchange between O-16-rich solids and O-16-poor gases prior to the final agglomeration of the CAI cannot be ruled out, we suggest that modification of chemical and isotopic composition of porous CAI precursors or aggregation of isotopically distinct mineral assemblages are alternative scenarios for the origin of oxygen isotopic heterogeneity in CAIs. In either case, coexistence of spatially and/or temporally distinct O-16-rich and O-16-poor gaseous reservoirs at the earliest stage of the solar system formation is required. The grain-scale oxygen isotopic disequilibrium in the CAI indicate that post-formation heating of the inclusion (i.e., the WL rim formation event) was short (e.g., less than or similar to 10(3) h at 1400 K; less than or similar to 10(5) h at 1100 K), which can be achieved by rapid outward transport of the CAI. High Ti3+/Ti-tot ratios of pyroxene from CAI interior and the rim and LIME composition of the olivine rim document that the entire CAI formation process took place under highly reducing conditions. (C) 2019 Elsevier Ltd. All rights reserved.
  • Noriyuki Kawasaki, Changkun Park, Naoya Sakamoto, Sun Young Park, Hyun Na Kim, Minami Kuroda, Hisayoshi Yurimoto
    Earth and Planetary Science Letters 511 25 - 35 2019年04月 [査読有り][通常論文]
     
    © 2019 Elsevier B.V. Al–Mg mineral isochrons of three Ca–Al-rich inclusions (CAIs) that formed primarily by condensation, one fine-grained, spinel-rich inclusion and two fluffy Type A CAIs, from the reduced CV chondrites Efremovka and Vigarano were obtained by in situ Al–Mg isotope measurements using secondary ion mass spectrometry. The slope of the isochron obtained for the fine-grained, spinel-rich inclusion gives an initial 26 Al/ 27 Al value, ( 26 Al/ 27 Al) 0 , of (5.19 ± 0.17) × 10 −5 . This is essentially identical to the Solar System initial 26 Al/ 27 Al determined by whole-rock Al–Mg isochron studies for CAIs in CV chondrites. In contrast, the isochron slopes for the two fluffy Type A CAIs from their Al–Mg mineral isochrons, (4.703 ± 0.082) × 10 −5 and (4.393 ± 0.084) × 10 −5 , are significantly lower than the Solar System initial value. The range of ( 26 Al/ 27 Al) 0 values of the three CAIs, from (5.19 ± 0.17) to (4.393 ± 0.084) × 10 −5 , corresponds to a formation age spread of 0.17 ± 0.04 Myr. This formation age spread is similar to that of igneous CAIs from CV chondrites. The data suggest that condensation and melting of minerals occurred in the hot nebular gas contemporaneously for ∼0.2 Myr at the very beginning of our Solar System, if 26 Al was distributed homogeneously in the CAI forming region. Alternatively, the observed variations in ( 26 Al/ 27 Al) 0 among fluffy Type A CAIs would also raise a possibility of heterogeneous distributions of 26 Al in the forming region.
  • Minami Kuroda, Shogo Tachibana, Naoya Sakamoto, Hisayoshi Yurimoto
    American Mineralogist 104 3 385 - 390 2019年03月01日 [査読有り][通常論文]
     
    © 2019 Walter de Gruyter GmbH, Berlin/Boston. Diffusion experiments of 2H2O at 900-750 °C and water vapor pressure of 50 bar found diffusion of water in SiO2 glass more than one order of magnitude faster than that reported previously. The fast diffusion profile of water was observed as an extended tail of the normal water diffusion profile by a line scan analysis with SIMS, and it can be fitted with a diffusion model with a constant diffusivity. The obtained fast diffusion coefficient suggests that the diffusion species responsible for the fast diffusion is not molecular hydrogen but molecular water. The diffusivity and activation energy for the fast water diffusion can be explained by the correlation between diffusivities of noble gases in silica glass and their sizes. Because noble gases diffuse through free volume in the glass structure, we conclude that molecular water can also diffuse through the free volume. The abundance of free volume in the silica glass structure estimated previously is higher than that of 2H observed in the fast diffusion in this study, suggesting that the free volume was not fully occupied by 2H2O under the present experimental condition. This implies that the contribution of the fast water diffusion to the total water transport in volcanic glass becomes larger under higher water vapor pressure conditions.
  • Zhang Ai-Cheng, Wang Shu-Zhou, Tomioka Naotaka, Lu Xian-Cai, Ding Zhi-Yuan, Ma Chi, Wang Peng, Chen Jia-Ni, Xu Sheng, Gu Li-Xin, Bai Yuan-Qiang, Li Yang, Sakamoto Naoya, Wang Ru-Cheng
    AMERICAN MINERALOGIST 104 1 150 - 157 2019年01月 [査読有り][通常論文]
  • Charline Lormand, Georg F. Zellmer, Károly Németh, Geoff Kilgour, Stuart Mead, Alan S. Palmer, Naoya Sakamoto, Hisayoshi Yurimoto, Anja Moebis
    Microscopy and Microanalysis 24 6 667 - 675 2018年12月01日 [査読有り][通常論文]
     
    © 2018 Microscopy Society of America. Crystals within volcanic rocks record geochemical and textural signatures during magmatic evolution before eruption. Clues to this magmatic history can be examined using crystal size distribution (CSD) studies. The analysis of CSDs is a standard petrological tool, but laborious due to manual hand-drawing of crystal margins. The trainable Weka segmentation (TWS) plugin in ImageJ is a promising alternative. It uses machine learning and image segmentation to classify an image. We recorded back-scattered electron (BSE) images of three volcanic samples with different crystallinity (35, 50 and ≥85 vol. %), using scanning electron microscopes (SEM) of variable image resolutions, which we then tested using TWS. Crystal measurements obtained from the automatically segmented images are compared with those of the manual segmentation. Samples up to 50 vol. % crystallinity are successfully segmented using TWS. Segmentation at significantly higher crystallinities fails, as crystal boundaries cannot be distinguished. Accuracy performance tests for the TWS classifiers yield high F-scores (>0.930), hence, TWS is a successful and fast computing tool for outlining crystals from BSE images of glassy rocks. Finally, reliable CSD's can be derived using a low-cost desktop SEM, paving the way for a wide range of research to take advantage of this new petrological method.
  • Yamamoto Daiki, Kuroda Minami, Tachibana Shogo, Sakamoto Naoya, Yurimoto Hisayoshi
    ASTROPHYSICAL JOURNAL 865 2 2018年10月01日 [査読有り][通常論文]
     
    Meteoritic evidence suggests that oxygen isotopic exchange between O-16-rich amorphous silicate dust and O-16-poor water vapor occurred in the early solar system. In this study, we experimentally investigated the kinetics of oxygen isotopic exchange between submicron-sized amorphous forsterite grains and water vapor at protoplanetary disk-like low pressures of water vapor. The isotopic exchange reaction rate is controlled either by diffusive isotopic exchange in the amorphous structure or by the supply of water molecules from the vapor phase. The diffusive oxygen isotopic exchange occurred with a rate constant D (m(2) s(-1)) = (1.5 +/- 1.0) x 10(-19) exp[-(161.5 +/- 14.1 (kJ mol(-1))) R-1(1/T-1/1200)] at temperatures below similar to 800-900 K, and the supply of water molecules from the vapor phase could determine the rate of oxygen isotopic exchange at higher temperatures in the protosolar disk. On the other hand, the oxygen isotopic exchange rate dramatically decreases if the crystallization of amorphous forsterite precedes the oxygen isotopic exchange reaction with amorphous forsterite. According to the kinetics for oxygen isotopic exchange in protoplanetary disks, original isotopic compositions of amorphous forsterite dust could be preserved only if the dust was kept at temperatures below 500-600 K in the early solar system. The O-16-poor signatures for the most pristine silicate dust observed in cometary materials implies that the cometary silicate dust experienced oxygen isotopic exchange with O-16-poor water vapor through thermal annealing at temperatures higher than 500-600 K prior to their accretion into comets in the solar system.
  • Kakizawa Sho, Inoue Toru, Nakano Hideto, Kuroda Minami, Sakamoto Naoya, Yurimoto Hisayoshi
    AMERICAN MINERALOGIST 103 8 1221 - 1227 2018年08月 [査読有り][通常論文]
     
    We determined the stability and chemical composition of Al-bearing superhydrous phase B at 20-24 GPa and 1400-2000 degrees C to discuss the mechanism of water transport in the mantle transition zone and uppermost lower mantle at temperatures close to the mantle geotherm. Superhydrous phase B contained significant amounts of Al2O3, from 14 to 32 wt%, and Al-bearing superhydrous phase B remained stable, even at 2000 degrees C and pressures of approximately 20-24 GPa. Moreover, two types of superhydrous phase B with different chemical compositions coexisted at 20-24 GPa and 1600 degrees C. The Al2O3 and H2O contents increased, and the MgO and SiO2 contents decreased as the pressure and temperature increased up to 1600 degrees C. Above 1600 degrees C, the MgO and Al2O3 contents increased, and the SiO2 and H2O contents decreased as the temperature increased. We found two substitution mechanisms: (1) 2Mg(2+) + Si4+ reversible arrow 2Al(3+) + 2H(+) + square(Mg) (Mg site vacancy) (2Mg(2+) = Al3+ + H+ + square(Mg)):(Si4+ = Al3+ + H+) = 1:1, (2) Si4+ + 16H(+) reversible arrow 4Mg(2+) + 4Al(3+). The maximum H2O content of Al-bearing superhydrous phase B is 11.1(3) wt%, which is similar to 1.9 times larger than that of the Mg-end-member. The crystal structures of the two coexisting superhydrous phase B values are expected to be slightly different from each other. The present results indicate that Al-bearing superhydrous phase B can be stable in a subducted slab with a high Al content compared to pyrolite (e.g, chlorite) at temperatures typical of the mantle transition zone and the lower mantle. Thus, water can be transported to the lower mantle by Al-bearing superhydrous phase B in the subducting slab, even at the typical mantle geotherm.
  • Matsuda N, Sakamoto N, Tachibana S, Yurimoto H
    METEORITICS & PLANETARY SCIENCE 53 6179  2018年08月 [査読有り][通常論文]
  • T. Yoshizaki, T. Nakamura, D. Nakashima, N. Sakamoto, H. Ishida, S. Itoh
    METEORITICS & PLANETARY SCIENCE 53 6012 - 6012 2018年08月 [査読有り][通常論文]
  • Minami Kuroda, Shogo Tachibana, Naoya Sakamoto, Satoshi Okumura, Michihiko Nakamura, Hisayoshi Yurimoto
    American Mineralogist 103 3 412 - 417 2018年03月26日 [査読有り][通常論文]
     
    Water diffusion in silicate melts is a fundamental process controlling physical and chemical consequences for magmatism, but mechanisms of diffusion in silicate glasses and melts are not fully understood. In this study, water diffusion experiments in silica glass were performed at temperatures of 650-850 °C and water vapor pressure of 50 bar, with the aim of improving our understanding of the mechanism of water diffusion in a simple SiO2-H2O system, and to construct a general water diffusion model for multi-component silicate glasses. Hydrogen diffusion profiles in silica glass were measured by secondary ion mass spectrometry (SIMS) down to a water concentration of ∼10 ppm. Water diffusion profiles indicate that water diffusion becomes slower with decreasing water concentration in silica glass, with the water concentration dependence being greater than in multi-component silicate glasses, particularly at low concentrations (e.g., Doremus 1969, 2000 Zhang and Behrens 2000). A new water diffusion model is proposed for silica glass, where the greater concentration dependence is attributed to the limited number of diffusion pathways in silica glass, formed by breaking Si-O-Si bonds through hydroxyl formation. The model was applied to multi-component silicate glasses, taking into account the effects of metal cations that act as network modifiers by providing additional diffusion pathways for water molecules. The lower water concentration dependence in multi-component silicate glasses and melts is explained by little dependence of the number of diffusion pathways on water concentration because it is controlled extrinsically by network modifier cations. It is concluded that the number of diffusion pathways is an essential controlling factor for water diffusion in silica and silicate glasses.
  • Wei Sun, Takashi Yoshino, Naoya Sakamoto, Hisayoshi Yurimoto
    Earth and Planetary Science Letters 484 309 - 317 2018年02月15日 [査読有り][通常論文]
     
    Knowledge of the distribution of water in the Earth's mantle is key to understanding the mantle convection and geochemical evolution of the Earth. As wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures, proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge, where descending slab stagnates at the transition zone. However, there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies, because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite. Here we report the hydrogen self-diffusion coefficient obtained from H–D interdiffusion experiments in wadsleyite single-crystal couples. Our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone. In contrast, the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle, probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales. This phenomenon provides an alternative explanation for both the high-conductivity and seismic-velocity anomalies observed in the mantle wedge at the transition-zone depth.
  • Hongzhan Fei, Michael Wiedenbeck, Naoya Sakamoto, Hisayoshi Yurimoto, Takashi Yoshino, Daisuke Yamazaki, Tomoo Katsura
    Physics of the Earth and Planetary Interiors 275 1 - 8 2018年02月01日 [査読有り][通常論文]
     
    Oxygen self-diffusion coefficients (DOx) were measured in single crystals of dry synthetic iron-free olivine (forsterite, Mg2SiO4) at a temperature of 1600 K and under pressures in the range 10−4 to 13 GPa, using a Kawai-type multi-anvil apparatus and an ambient pressure furnace. Diffusion profiles were obtained by secondary ion mass spectrometry operating in depth profiling mode. DOx in forsterite increases with increasing pressure with an activation volume of −3.9 ± 1.2 cm3/mol. Although Mg is the fastest diffusing species in forsterite under low-pressure conditions, O is the fastest diffusing species at pressures greater than ∼10 GPa. Si is the slowest throughout the stable pressure range of forsterite. Based on the observed positive and negative pressure dependence of DOx and DMg (Mg self-diffusion coefficient), respectively, DOx + DMg in forsterite decreases with increasing pressure, and then increases slightly at pressures greater than 10 GPa. This behavior is in agreement with the pressure dependence of ionic conductivity in forsterite based on conductivity measurements (Yoshino et al., 2017), and can be used to explain the conductivity increase from ∼300 km depth to the bottom of the asthenosphere.
  • Noriyuki Kawasaki, Steven B. Simon, Lawrence Grossman, Naoya Sakamoto, Hisayoshi Yurimoto
    Geochimica et Cosmochimica Acta 221 318 - 341 2018年01月15日 [査読有り][通常論文]
     
    TS34 is a Type B1 Ca-Al-rich inclusion (CAI) from the Allende CV3 chondrite, consisting of spinel, melilite, Ti-Al-rich clinopyroxene (fassaite) and minor anorthite in an igneous texture. Oxygen and magnesium isotopic compositions were measured by secondary ion mass spectrometry in spots of known chemical composition in all major minerals in TS34. Using the sequence of formation from dynamic crystallization experiments and from chemical compositions of melilite and fassaite, the oxygen isotopic evolution of the CAI melt was established. Oxygen isotopic compositions of the constituent minerals plot along the carbonaceous chondrite anhydrous mineral line. The spinel grains are uniformly 16O-rich (Δ17O = −22.7 ± 1.7‰, 2SD), while the melilite grains are uniformly 16O-poor (Δ17O = −2.8 ± 1.8‰) irrespective of their åkermanite content and thus their relative time of crystallization. The fassaite crystals exhibit growth zoning overprinting poorly-developed sector zoning they generally grow from Ti-rich to Ti-poor compositions. The fassaite crystals also show continuous variations in Δ17O along the inferred directions of crystal growth, from 16O-poor (Δ17O ∼ −3‰) to 16O-rich (Δ17O ∼ −23‰), covering the full range of oxygen isotopic compositions observed in TS34. The early-crystallized 16O-poor fassaite and the melilite are in oxygen isotope equilibrium and formed simultaneously. The correlation of oxygen isotopic compositions with Ti content in the fassaite imply that the oxygen isotopic composition of the CAI melt evolved from 16O-poor to 16O-rich during fassaite crystallization, presumably due to oxygen isotope exchange with a surrounding 16O-rich nebular gas. Formation of spinel, the liquidus phase in melts of this composition, predates crystallization of all other phases, so its 16O-rich composition is a relic of an earlier stage. Anorthite exhibits oxygen isotopic compositions between Δ17O ∼ −2‰ and −9‰, within the range of those of fassaite, indicating co-crystallization of these two minerals during the earliest to intermediate stage of fassaite growth. The melilite and fassaite yield an 26Al–26Mg mineral isochron with an initial value of (26Al/27Al)0 = (5.003 ± 0.075) × 10−5, corresponding to a relative age of 0.05 ± 0.02 Myr from the canonical Al–Mg age of CAIs. These data demonstrate that both 16O-rich and 16O-poor reservoirs existed in the solar nebula at least ∼0.05 Myr after the birth of the Solar System.
  • Ai-Cheng Zhang, Yi-Fan Bu, Run-Lian Pang, Naoya Sakamoto, Hisayoshi Yurimoto, Li-Hui Chen, Jian-Feng Gao, De-Hong Du, Xiao-Lei Wang, Ru-Cheng Wang
    GEOCHIMICA ET COSMOCHIMICA ACTA 220 125 - 145 2018年01月 [査読有り][通常論文]
     
    Troilite-orthopyroxene intergrowths are present as a common material in the brecciated diogenite Northwest Africa (NWA) 7183. In this study, we report on the petrographic, mineralogical, and rare earth element abundances of the troilite-orthopyroxene intergrowths to constrain their origin and assess their implications for the diverse petrogenesis of diogenites.Two groups of troilite-orthopyroxene intergrowths with various grain sizes and mineral chemistry have been observed in NWA 7183. One group of intergrowths contains fine-grained (<5 mu m) olivine and chromite as inclusions in orthopyroxene (10-20 mu m in size). The other group, in which orthopyroxene is more fine-grained (<10 mu m in size), is closely associated with coarse irregular olivine grains. The orthopyroxene grains in both groups of troilite-orthopyroxene intergrowths are depleted in Cr, Al, Ti, and Ca compared with diogenitic orthopyroxene. Based on the texture and mineral chemistry, we suggest that the two groups of troilite-orthopyroxene intergrowths formed via reactions between diogenitic olivine and S-rich vapors, probably at different temperatures. The fact that some of the intergrowths are included in diogenitic lithic clasts indicates that the formation of the host diogenite should postdate the formation of the majority of troilite-orthopyroxene intergrowths. This relationship further implies that not all of the diogenites are cumulates that directly crystallized from the Vestan magma ocean. Instead, they probably originated from partial melting and recrystallization of magma ocean cumulates. The replacement of olivine by troilite and orthopyroxene intergrowths can partly explain why the expected olivine-rich lithologies were not detected at the two south pole impact basins on Vesta. (C) 2017 Elsevier Ltd. All rights reserved.
  • Georg F. Zellmer, Naoya Sakamoto, Nozomi Matsuda, Yoshiyuki Iizuka, Anja Moebis, Hisayoshi Yurimoto
    GEOCHIMICA ET COSMOCHIMICA ACTA 220 552 - 553 2018年01月 [査読有り][通常論文]
  • Fei, H., Koizumi, S., Sakamoto, N., Hashiguchi, M., Yurimoto, H., Marquardt, K., Miyajima, N., Katsura, T.
    Earth and Planetary Science Letters 484 204 - 212 2018年 [査読有り][通常論文]
  • Haruka Ozawa, Shigehiko Tateno, Longjian Xie, Yoichi Nakajima, Naoya Sakamoto, Saori I. Kawaguchi, Akira Yoneda, Naohisa Hirao
    HIGH PRESSURE RESEARCH 38 2 120 - 135 2018年 [査読有り][通常論文]
     
    We have developed an internal-resistive heated diamond-anvil cell (IHDAC) with a new resistance heater - boron-doped diamond (BDD) - along with an optimized design of the cell assembly, including a composite gasket. Our proposed technique is capable of heating a silicate/oxide material with (1) long-term stability (>1h at 2500K) and (2) uniform radial temperature distribution (+/- 35K at 2500K across a 40-mu m area), which are clear advantages over the conventional laser-heated and internal-heated DACs. In addition, the achieved temperature in this study was greater than 3500K, which mostly covers the possible geotherm of the entire lower mantle. In situ X-ray diffraction (XRD) measurement and ex situ chemical analyses confirmed that weak XRD intensity from the BDD heater and chemical inertness (no boron diffusion into silicate samples). This newly developed IHDAC with a BDD heater can be used to determine the phase diagrams of mantle materials with high precision and be used in lower-mantle petrology.
  • Fei, H., Koizumi, S., Sakamoto, N., Hashiguchi, M., Yurimoto, H., Marquardt, K., Miyajima, N., Katsura, T.
    American Mineralogist 103 9 1354 - 1361 2018年 [査読有り][通常論文]
  • Hikaru Yabuta, Takaaki Noguchi, Shoichi Itoh, Tomoki Nakamura, Akira Miyake, Shinichi Tsujimoto, Noriaki Ohashi, Naoya Sakamoto, Minako Hashiguchi, Ken-ichi Abe, Aya Okubo, A. L. David Kilcoyne, Shogo Tachibana, Ryuji Okazaki, Kentaro Terada, Mitsuru Ebihara, Hiroko Nagahara
    GEOCHIMICA ET COSMOCHIMICA ACTA 214 172 - 190 2017年10月 [査読有り][通常論文]
     
    A comprehensive study of the organic chemistry and mineralogy of an ultracarbonaceous micrometeorite (UCAMM D05IB80) collected from near the Dome Fuji Station, Antarctica, was carried out to understand the genetic relationship among organic materials, silicates, and water. The micrometeorite is composed of a dense aggregate of similar to 5 mm-sized hollow ellipsoidal organic material containing submicrometer-sized phases such as glass with embedded metal and sulfides (GEMS) and mineral grains. There is a wide area of organic material (similar to 15 x 15 mu m) in its interior. Low-Ca pyroxene is much more abundant than olivine and shows various Mg/(Mg + Fe) ratios ranging from similar to 1.0 to 0.78, which is common to previous works on UCAMMs. By contrast, GEMS grains in this UCAMM have unusual chemical compositions. They are depleted in both Mg and S, which suggests that these elements were leached out from the GEMS grains during very weak aqueous alteration, without the formation of phyllosilicates. The organic materials have two textures-smooth and globular with an irregular outline- and these are composed of imine, nitrile and/or aromatic nitrogen heterocycles, and amide. The ratio of nitrogen to carbon (N/C) in the smooth region of the organics is similar to 0.15, which is five times higher than that of insoluble organic macromolecules in types 1 and 2 carbonaceous chondritic meteorites. In addition, the UCAMM organic materials are soluble in epoxy and are thus hydrophilic; this polar nature indicates that they are very primitive. The surface of the material is coated with an inorganic layer, a few nanometers thick, that consists of C, O, Si, S, and Fe. Sulfur is also contained in the interior, implying the presence of organosulfur moieties. There are no isotopic anomalies of D, C-13, or N-15 in the organic material. Interstellar photochemistry alone would not be sufficient to explain the N/C ratio of the UCAMM organics; therefore, we suggest that a very small amount of fluid on a comet must have been necessary for the formation of the UCAMM. The GEMS grains depleted in Mg and S in the UCAMM prove a very weak degree of aqueous alteration; weaker than that of carbonaceous chondrites. Short-duration weak alteration probably caused by planetesimal shock locally melted cometary ice grains and released water that dissolved the organics; the fluid would likely have not mobilized because of the very low thermal conductivity of the porous icy body. This event allowed the formation of the large organic puddle of the UCAMM, as well as organic matter sulfurization, formation of thin membrane-like layers of minerals, and deformation of organic nanoglobules. (C) 2017 Elsevier Ltd. All rights reserved.
  • T. Yoshizaki, D. Nakashima, T. Nakamura, H. Ishida, N. Sakamoto
    METEORITICS & PLANETARY SCIENCE 52 A400 - A400 2017年08月 [査読有り][通常論文]
  • T. Noguchi, H. Yabuta, S. Itoh, N. Sakamoto, T. Mitsunari, A. Okubo, R. Okazaki, T. Nakamura, S. Tachibana, K. Terada, M. Ebihara, N. Imae, M. Kimura, H. Nagahara
    GEOCHIMICA ET COSMOCHIMICA ACTA 208 1 119 - 144 2017年07月 [査読有り][通常論文]
     
    Micrometeorites (MMs) recovered from surface snow near the Dome Fuji Station, Antarctica are almost free from terrestrial weathering and contain very primitive materials, and are suitable for investigation of the evolution and interaction of inorganic and organic materials in the early solar system. We carried out a comprehensive study on seven porous and fluffy MMs [ four Chondritic porous (CP) MMs and three fluffy fine-grained (Fluffy Fg) MMs] and one fine-grained type 1 (Fg C1) MM for comparison with scanning electron microscope, transmission electron microscope, X-ray absorption near-edge structure analysis, and secondary ion mass spectrometer. They show a variety of early aqueous activities. Four out of the seven CP MMs contain glass with embedded metal and sulfide (GEMS) and enstatite whiskers/platelets and do not have hydrated minerals. Despite the same mineralogy, organic chemistry of the CP MMs shows diversity. Two of them contain considerable amounts of organic materials with high carboxyl functionality, and one of them contains nitrile (CBN) and/or nitrogen heterocyclic groups with D and N-15 enrichments, suggesting formation in the molecular cloud or a very low temperature region of the outer solar system. Another two CP MMs are poorer in organic materials than the above-mentioned MMs. Organic material in one of them is richer in aromatic C than the CP MMs mentioned above, being indistinguishable from those of hydrated carbonaceous chondrites. In addition, bulk chemical compositions of GEMS in the latter organic poor CP MMs are more homogeneous and have higher Fe/(Si + Mg + Fe) ratios than those of GEMS in the former organic-rich CP MMs. Functional group of the organic materials and amorphous silicate in GEMS in the organic-poor CP MMs may have transformed in the earliest stage of aqueous alteration, which did not form hydrated minerals. Three Fluffy Fg MMs contain abundant phyllosilicates, showing a clear evidence of aqueous alteration. Phyllosilicates in thee MMs are richer in Fe than those in hydrated IDPs, typical fine-grained hydrated (Fg C1) MMs, and hydrated carbonaceous chondrites. One of the Fluffy Fg MMs contains amorphous silicate, which is richer in Fe than GEMS and contains little or no nanophase Fe metal but contains Fe sulfide. Because the chemical compositions of the amorphous silicate are within the compositional field of GEMS in CP IDPs, the amorphous silicate may be alteration products of GEMS. The entire compositional field of GEMS in the CP MMs and the amorphous silicate in the Fluffy Fg MM matches that of the previously reported total compositional range of GEMS in IDPs. One Fluffy Fg MM contains Mg-rich phyllosilicate along with Fe-rich phyllosilicate and Mg-Fe carbonate. Mg-rich phyllosilicate and Mg-Fe carbonate may have been formed through the reaction of Fe-rich phyllosilicate, Mg-rich olivine and pyroxene, and water with C-bearing chemical species. These data indicate that CP MMs and Fluffy Fg MMs recovered from Antarctic surface snow contain materials that throw a light on the earliest stages of aqueous alteration on very primitive solar system bodies. Because mineralogy and isotopic and structural features of organic materials in D10IB009 are comparable with isotopically primitive IDPs, its parent body could be comets or icy asteroids showing mass ejection (active asteroids). By contrast, organic-poor CP MMs may have experienced the earliest stage of aqueous alteration and Fluffy Fg MMs experienced weak aqueous alteration. The precursor materials of the parent bodies of Fluffy Fg MMs probably contained abundant GEMS or GEMS-like materials like CP IDPs, which is common to fine-grained matrices of very primitive carbonaceous chondrites such as CR3s. However, highly porous nature of organic-poor CP MMs and Fluffy Fg MMs suggests that parent bodies of these MMs must have been much more porous than the parent bodies of primitive carbonaceous chondrites. Given no phyllosilicate among the returned samples of 81P/Wild 2 comet, the MMs may have been derived from porous icy asteroids such as active asteroids as well as P-and D-type asteroids rather than comets. (C) 2017 Elsevier Ltd. All rights reserved.
  • Kawasaki Noriyuki, Itoh Shoichi, Sakamoto Naoya, Yurimoto Hisayoshi
    Geochimica et cosmochimica acta 201 201 83 - 102 Elsevier 2017年03月15日 [査読有り][通常論文]
  • Fang Xu, Daisuke Yamazaki, Naoya Sakamoto, Wei Sun, Hongzhan Fei, Hisayoshi Yurimoto
    EARTH AND PLANETARY SCIENCE LETTERS 459 332 - 339 2017年02月 [査読有り][通常論文]
     
    Diffusion of Si and 0 in single crystal stishovite was examined at pressures of 14.0-21.5 GPa and temperatures of 1673-2073 K. Self-diffusion coefficients of Si (D-si) and O (D-o) were determined as D-si; [m(2)/s] = 2.4 x 10(-12) exp{-(237 [kJ/mol] + 6.0 [cm(3)/mol] x P)/RT} and D-o [m(2)/s] = 7.2 x 10(-11) exp{-(263 [kJ/mol] + 4.8 [cm(3)/mol] x P)/RT}, respectively, where P is pressure (in GPa), T is absolute temperature (in K) and R is the ideal gas constant. It was revealed that diffusion of Si is approximately one order of magnitude slower than that of 0 and, thus, Si is the rate-controlling element for plastic deformation of stishovite. Si diffusion in stishovite is assessed to be at least three orders of magnitude slower than that in bridgmanite under mid-mantle conditions. Therefore, it is anticipated that highly viscous SiO2-rich components subducted into the lower mantle persist as the seismic reflectors for long term without mixing up with the bridgmanite-dominated surrounding mantle. (C) 2016 Elsevier B.V. All rights reserved.
  • Jack A. Singer, James P. Greenwood, Shoichi Itoh, Naoya Sakamoto, Hisayoshi Yurimoto
    GEOCHEMICAL JOURNAL 51 1 95 - 104 2017年 [査読有り][通常論文]
     
    While it is now recognized that the Moon has indigenous water and volatiles, their total abundances are unclear, with current literature estimates ranging from nearly absent to Earth-like levels. Similarly unconstrained is the source of the Moon's water, which could be cometary, chondritic, or the primordial nebula. Here we measure H2O and D/H in olivine-hosted melt inclusions in lunar mare basalts 12018, 12035, and 12040, part of the consanguineous suite of Apollo 12 olivine basalts that differ primarily because of cooling rate (Walker et al., 1976). We find that the water contents are higher in the more rapidly cooled 12018 (62-740 ppm H2O) compared to the more slowly cooled basalts 12035 (28-156 ppm H2O) and 12040 (27-90 ppm H2O), suggesting that lunar basalts may have been dehydrating during slow cooling. D/H is similar in the olivine-hosted melt inclusions in all three samples, and indistinguishable from terrestrial water (dD = -183 +/- 212% to + 138 +/- 61%). When we compare the D/H of olivine-hosted melt inclusions to D/H of apatite in the same samples, the evolution of dD and water content can be better constrained. We propose that lunar magmas first exchange hydrogen with a low D/H reservoir during cooling, and then ultimately lose their water during extended subsolidus cooling. Due to high diffusion rates of hydrogen in olivine, it is likely that all basaltic olivine-hosted melt inclusions from the Moon exchanged hydrogen with a low D/H reservoir in near-surface magma chambers or lava flows. The most likely source of the low D/H reservoir on the Moon is the lunar regolith, which is known to have a significant solar wind hydrogen component.
  • Kenichi Abe, Naoya Sakamoto, Alexander N. Krot, Hisayoshi Yurimoto
    GEOCHEMICAL JOURNAL 51 1 3 - 15 2017年 [査読有り][通常論文]
     
    We describe the petrographic occurrences, abundances, and compositional variations of symplectically intergrown Fe, Ni-sulfides and O-17,O-18-rich magnetite (Delta O-17 similar to 90 parts per thousand), named cosmic symplectites (COS; Sakamoto et al., 2007), from the Acfer 094 (C3.0) ungrouped carbonaceous chondrite. A total of 314 COS studied in two polished sections of this meteorite are uniformly distributed in its matrix with similar to 600 ppm surface area abundance. No COS have been identified in the Acfer 094 dark inclusions (chondritic lithic clasts) which appear to have experienced extensive aqueous alteration prior to incorporation into the host meteorite. The structure of COS can be arranged in a hierarchy of four categories (from finer to coarser): (1) symplectite structure composed of nanocrystalline magnetite and Fe, Ni-sulfides, (2) submicronsized wormy structure composed of nanocrystalline symplectites, (3) micrometer-sized irregular rope-like structure composed of wormy structure, and (4) aggregates of the rope-like structure. COS typically associate with fractured Fe, Ni-sulfides and lack Fe, Ni-metal. Most COS studied have smooth surfaces; four grains contain abundant pores. In a single COS, the pore-rich regions are depleted in sulfur and nickel relative to the pore-free regions, indicating that the former are depleted in Fe, Ni-sulfides. Most COS studied contain similar abundances of Fe, Ni-sulfides and magnetite, whereas Ni/(Fe+Ni) atomic ratio in Fe, Ni-sulfides ranges from 0 to 0.4. The lack of Fe, Ni-metal associated with COS supports the formation process proposed by Seto et al. (2008), i.e., oxidation of Fe, Ni-metal and sulfides by O-17,O-18-rich water vapor in the outer part of the protoplanetary disk. The similar abundance ratio for Fe, Ni-sulfide and magnetite cannot be simply explained by oxidation processes of Fe, Ni-sulfide precursors after sulfurization of Fe, Ni-metal precursors for COS formation as proposed by Seto et al. (2008).
  • James P. Greenwood, Naoya Sakamoto, Shoichi Itoh, Paul H. Warren, Jack A. Singer, Kaori Yanai, Hisayoshi Yurimoto
    GEOCHEMICAL JOURNAL 51 1 105 - 114 2017年 [査読有り][通常論文]
     
    The last liquids of the lunar magma ocean, known as urKREEP, should be highly enriched in volatiles, such as water, fluorine, and chlorine. We find chlorine-rich glasses in two pristine KREEP basalts from the Moon and calculate the volatile contents of the urKREEP component, and use this to estimate the fluorine and chlorine content of the lunar magma ocean. The Cl/Nb and F/Nd of KREEP imply that the lunar magma ocean was depleted in fluorine and chlorine by an order of magnitude compared to the Earth's mantle. The extremely dry nature of most lunar samples is simply a result of partial melting of magma ocean cumulates that had already lost their volatiles to the urKREEP layer. The volatile-rich KREEP component may have helped lower the solidus of high-temperature magma ocean cumulates that were melted to form the Mg-suite rocks of the highlands, and also aided the dissemination of the KREEP signature into the upper crust. The chlorine-rich KREEP glasses also demonstrate that the large chlorine isotope anomaly found in lunar samples is likely an early lunar signature.
  • Ai-Cheng Zhang, Qiu-Li Li, Hisayoshi Yurimoto, Naoya Sakamoto, Xian-Hua Li, Sen Hu, Yang-Ting Lin, Ru-Cheng Wang
    NATURE COMMUNICATIONS 7 12844 - 12844 2016年09月 [査読有り][通常論文]
     
    Chondritic meteorites, consisting of the materials that have formed in the early solar system (ESS), have been affected by late thermal events and fluid activity to various degrees. Determining the timing of fluid activity in ESS is of fundamental importance for understanding the nature, formation, evolution and significance of fluid activity in ESS. Previous investigations have determined the relative ages of fluid activity with short-lived isotope systematics. Here we report an absolute Pb-207/Pb-206 isochron age (4,450 +/- 50 Ma) of apatite from Dar al Gani (DaG) 978, a type similar to 3.5, ungrouped carbonaceous chondrite. The petrographic, mineralogical and geochemical features suggest that the apatite in DaG 978 should have formed during metamorphism in the presence of a fluid. Therefore, the apatite age represents an absolute age for fluid activity in an asteroidal setting. An impact event could have provided the heat to activate this young fluid activity in ESS.
  • Georg F. Zellmer, Naoya Sakamoto, Shyh-Lung Hwang, Nozomi Matsuda, Yoshiyuki Iizuka, Anja Moebis, Hisayoshi Yurimoto
    FRONTIERS IN EARTH SCIENCE 4 2016年09月 [査読有り][通常論文]
     
    Crystal nucleation and growth are first order processes captured in volcanic rocks and record important information about the rates of magmatic processes and chemical evolution of magmas during their ascent and eruption. We have studied glass-rich andesitic tephras from the Central Plateau of the Southern Taupo Volcanic Zone by electron- and ion-microbeam imaging techniques to investigate down to sub-micrometer scale the potential effects of compositional boundary layers (CBLs) of melt around crystals on the nucleation and growth of mineral phases and the chemistry of crystal growth zones. We find that CBLs may influence the types of mineral phases nucleating and growing, and growth textures such as the development of swallowtails. The chemistry of the CBLs also has the capacity to trigger intermittent overgrowths of nanometer-scale bands of different phases in rapidly growing crystals, resulting in what we refer to as cryptic phase zoning. The existence of cryptic phase zoning has implications for the interpretation of microprobe compositional data, and the resulting inferences made on the conditions of magmatic evolution. Identification of cryptic phase zoning may improve thermobarometric estimates and thus geospeedometric constraints. In future, a more quantitative characterization of CBL formation and its effects on crystal nucleation and growth may contribute to a better understanding of melt rheology and magma ascent processes at the onset of explosive volcanic eruptions, and will likely be of benefit to hazard mitigation efforts.
  • Georg F. Zellmer, Naoya Sakamoto, Nozomi Matsuda, Yoshiyuki Iizuka, Anja Moebis, Hisayoshi Yurimoto
    GEOCHIMICA ET COSMOCHIMICA ACTA 185 383 - 393 2016年07月 [査読有り][通常論文]
     
    Using a high resolution ion microprobe with SCAPS imaging, the peritectic reaction of forsterite + silica to enstatite was studied down to submicron level in a natural andesitic tephra from the Central Plateau of North Island, New Zealand. The fayalitic component of natural olivines is stable in high-silica melts, and therefore the reaction is in fact a two-step progress: 1. Dissolution of Mg-rich olivine, rate-limited by Fe-Mg interdiffusion at the crystal rim, results in enrichment of Fe in the crystal rim and of Mg in the c.1 mu m wide melt boundary layer around the crystal. 2. Magnesian pyroxenes preferentially but not exclusively nucleate in the melt boundary layer and grow; as soon as these microlites touch the rim of the dissolving olivine, they shield the crystals from the silica-rich melt, thereby preventing further olivine dissolution. At this point, Fe- Mg interdiffusion begins to destroy the Fe- enrichment of the olivine rim. The reaction is completed when the dissolving olivine crystal is completely mantled by magnesian pyroxene microlites. Thick pyroxene mantles are likely the result of pyroxene overgrowth rather than due to peritectic transformation. The morphology of the olivine rim preserves information about the reaction history of the grain. Modeling of Fe-Mg interdiffusion in the olivine rim following its shielding from the melt by pyroxene overgrowth may yield the rates of olivine dissolution and the rates of pyroxene growth if temperature is known. For the tephra we have studied, microlite thermometry yields a temperature of 1137 (+/- 41) degrees C, indicating an olivine dissolution rate of 3-6 x 10(-11) ms(-1) and an initially volumetric pyroxene growth rate of 2.2-5.6 x 10(-21) m(3) s(-1). This points to timescales between olivine crystal uptake into the SiO2-rich melt and explosive eruption at the surface of a few hours to at most a day. (C) 2016 Elsevier Ltd. All rights reserved.
  • Steeve Greaux, Yoshio Kono, Yanbin Wang, Akihiro Yamada, Chunyin Zhou, Zhicheng Jing, Toru Inoue, Yuji Higo, Tetsuo Irifune, Naoya Sakamoto, Hisayoshi Yurimoto
    GEOPHYSICAL RESEARCH LETTERS 43 9 4239 - 4246 2016年05月 [査読有り][通常論文]
     
    The elasticity of Al-bearing stishovite with 1.0, 3.3, and 4.5wt% Al2O3 was investigated in the multianvil apparatus at high pressures and temperatures up to 21GPa and 1700 K, by ultrasonic interferometry in conjunction with in situ X-ray techniques. The moduli K-S and G are found to decrease with increasing Al2O3 content, while their pressure and temperature derivatives do not change in a significant manner for 1.0 and 3.3 wt% Al2O3. The temperature derivatives for 4.5 wt% Al2O3, however, are larger, which may result from a change in the Al substitution mechanism at high Al2O3 content. It is shown that acoustic velocities of any mid-ocean ridge basalt are lower by -0.4% than those calculated from pure stishovite data. Velocity perturbations up to -3.4% (V-P) and -4.2% (VS) in subducted slabs are explained by the combination of the thermal equilibration (Delta T similar to 600 K) of the slab and Al enrichment in stishovite.
  • Fei, H., Koizumi, S., Sakamoto, N., Hashiguchi, M., Yurimoto, H., Marquardt, K., Miyajima, N., Yamazaki, D., Katsura, T.
    Earth and Planetary Science Letters 433 350 - 359 2016年 [査読有り][通常論文]
  • Ai-Cheng Zhang, Chi Ma, Naoya Sakamoto, Ru-Cheng Wang, Wei-Biao Hsu, Hisayoshi Yurimoto
    GEOCHIMICA ET COSMOCHIMICA ACTA 163 27 - 39 2015年08月 [査読有り][通常論文]
     
    Titanium-rich minerals are common in Ca-Al-rich inclusions from primitive chondrites. They are important not only for testing the condensation models for a gas with a solar composition, but also for constraining the redox conditions of the early solar nebula. In this study, we report the detailed mineralogical features and its oxygen isotope compositions of a Ti-Sc-rich ultrarefractory inclusion A0031 from a CH3 chondrite Sayh al Uhaymir 290. The A0031 inclusion has a compact and layered texture with the interior consisting of panguite, Sc-rich anosovite, Ti-rich davisite, and anorthite. A few hexaferrum, perovskite, and spinel crystals are present as inclusions in these minerals. Outside of Ti-rich davisite are a layer of Al-Ti-rich diopside and two grains of enstatite. This texture strongly suggests that A0031 has a condensation origin. Panguite is its third occurrence in nature and similar in composition to the type panguite from the Allende meteorite. Sc-rich anosovite in A0031 has a chemical formula of (Ti4+, Ti3+, Mg, Sc, Al)(3)O-5 with the pseudobrookite structure. This is the second report of Ti3O5 in nature, but is the first description of anosovite formed in the solar nebula as an ultrarefractory phase. The discovery of Sc-rich anosovite in A0031 reveals the stability of Ti3O5 in the early solar nebula and supports the prediction of previous equilibrium condensation calculations. The panguite, Sc-rich anosovite, and Ti-rich davisite in A0031 show a large variation in Ti3+/Ti-tot. The primitive nature of A0031 implies that the variations in Ti3+/Titot among different Ti-rich minerals are primary features. We propose that the distribution of Ti3+ and Ti4+ could be controlled mainly by their various competition abilities of incorporating into these Ti-Sc-Al-rich minerals. Similarity of Ti3+/Ti-tot value between Ti-rich davisite from A0031 and those in other carbonaceous chondrites indicates that most refractory inclusions might have formed in highly reducing nebular settings. The O-16-depleted isotope compositions of A0031 confirm the existence of diverse oxygen reservoirs for CH Ca-Al-rich inclusions in the solar nebula. (C) 2015 Elsevier Ltd. All rights reserved.
  • Wei Sun, Takashi Yoshino, Naoya Sakamoto, Hisayoshi Yurimoto
    GEOPHYSICAL RESEARCH LETTERS 42 16 6582 - 6589 2015年08月 [査読有り][通常論文]
     
    Hydrogen lattice diffusion in Fe-bearing ringwoodite was investigated through hydrogen and deuterium interdiffusing in a pair of synthesized single crystals at various temperatures (1000-1300 K) at 21 GPa. Diffusion profiles were investigated by secondary ion mass spectrometer to determine the hydrogen self-diffusivity in ringwoodite. Temperature dependences of hydrogen diffusion in ringwoodite were determined to be D-H=10(-7.29(+/- 0.46)) exp[-101(+/- 10) kJ mol(-1)/RT] m(2)/s in ringwoodite at 21GPa. The proton conductivities of ringwoodite estimated from the present diffusion coefficients are similar to those of Yoshino et al. [2008] at the transition zone condition at low water content (<1000 ppm by weight (ppmw)) but lower at higher water content range (>1000 ppmw). If the proton-vacancy mechanism is assumed to be a main controlling mechanism, contribution of water to the electrical conductivity of ringwoodite is insignificant due to large contribution of hopping conduction at the transition zone condition, and global average water concentration in the lower part of transition zone is less than 1000 ppmw.
  • Takuo Okuchi, Narangoo Purevjav, Naotaka Tomioka, Jung-Fu Lin, Takahiro Kuribayashi, Louise Schoneveld, Huijeong Hwang, Naoya Sakamoto, Noriyuki Kawasaki, Hisayoshi Yurimoto
    AMERICAN MINERALOGIST 100 7 1483 - 1492 2015年07月 [査読有り][通常論文]
     
    The presence of water in the Earth's deep mantle is an issue of increasing interest in the field of high-pressure mineralogy. An important task for further advancing research in the field is to create homogeneous single crystals of candidate deep-mantle water-bearing minerals of 1 mm or larger in size, which is required for applying them for the time-of-flight (TOE) single-crystal Laue diffraction method with a third-generation neutron instrument. In this study, we perform several experiments to demonstrate an improved methodology for growing hydrous crystals of such large sizes at relevant transition zone and lower-mantle conditions via very slow cooling over a maximum period of 1 day. Successfully synthesized crystals using this methodology include dense hydrous magnesium silicate (DHMS) phase E, hydrous wadsleyite, hydrous ringwoodite, and bridgmanite (silicate perovskite). It is also demonstrated that these hydrous crystals can be grown from deuterium enriched starting materials in addition to those having a natural hydrogen isotope ratio. Magnitudes of chemical and crystallographic heterogeneities of the product crystals were characterized by comprehensive analysis of X-ray precession photography, single-crystal X-ray diffraction (SCXRD), field-emission scanning electron microscope (FE-SEM), electron probe microanalyzer (EPMA), secondary ion mass spectroscopy (SIMS)(,) powder X-ray diffraction (PXRD), and TOF neutron powder diffraction (TOF-NPD). The product crystals were confirmed to be inclusion free and crystallographically homogeneous. Compositional and isotopic differences of major elements and hydrogen isotope abundances were lower than 1 and 3%, respectively, among intracrystals and intercrystals within each recovered sample capsule. Phase E crystals up to 600 mu m in the largest dimension were grown at a constant temperature of 1100 degrees C kept for 3 h. Using a lattice parameter-to-temperature relation of phase E, the thermal gradient in the sample capsules for the phase E synthesis has been evaluated to be 20 degrees C/mm. Hydrous wadsleyite crystals up to 1100 gm in the largest dimension were grown at 1390 degrees C with a temperature reduction of 70 degrees C during heating for 10 h. Hydrous ringwoodite crystals up to 1000 mu m in the largest dimension were grown at around 1400 degrees C with a temperature reduction of 110 degrees C during heating for 12 h. Bridgmanite crystals up to 600 mu m in the largest dimension were grown at 1700 degrees C with a temperature reduction of 30 degrees C during heating for 12 h. A TOF single-crystal diffraction instrument has been successfully used for analyzing one of the hydrous wadsleyite crystals, which demonstrated that single crystals appropriate for their expected usage are created using the method proposed in the present study.
  • Susumu Umino, Keitaro Kitamura, Kyoko Kanayama, Akihiro Tamura, Naoya Sakamoto, Osamu Ishizuka, Shoji Arai
    GEOLOGY 43 2 151 - 154 2015年02月 [査読有り][通常論文]
     
    Primitive melt inclusions in chrome spinel from the Ogasawara Archipelago (Japan) compose two discrete groups of high-SiO2, high-MgO (high-Si) and low-SiO2, low-MgO (low-Si) boninitic suites, with ultra-depleted dish-and V-shaped, and less-depleted flat, rare earth element patterns. The most magnesian melt inclusions of each geochemical type were used to estimate the temperature-pressure conditions for primary boninites, which range from 1345 degrees C at 0.56 GPa to 1421 degrees C at 0.85 GPa for the 48-46 Ma low-Si and high-Si boninites, and 1381 degrees C at 0.85 GPa for the 45 Ma low-Si boninite. The onset of the Pacific slab subduction at 52 Ma forced upwelling of depleted mid-oceanic ridge basalt mantle (DMM) to yield proto-arc basalt (PAB). With the rise of DMM, refractory harzburgite ascended without melting. At 48-46 Ma, introduction of slab fluids induced melting of the PAB residue and high-temperature harzburgite, resulting in the low-Si and high-Si boninites, respectively. Meanwhile, convection within the mantle wedge brought the less-depleted residue of PAB and DMM into the region fluxed by slab fluids, which melted to yield the less-depleted low-Si boninite at 45 Ma, and fertile arc basalts, respectively.
  • Georg F. Zellmer, Shyh-Lung Hwang, Naoya Sakamoto, Yoshiyuki Iizuka, Sakiko Harada, Jun-Ichi Kimura, Yoshihiko Tamura, Hisayoshi Yurimoto
    Geological Society Special Publication 410 1 219 - 236 2015年 [査読有り][通常論文]
     
    Pleistocene basalts from Daisen and Mengameyama in the SW Japan volcanic arc of western Honshu are characterized by an abundance of olivine crystals with Fe-rich rims. At Daisen, these have previously been interpreted to have formed from their host melt by equilibrium crystal fractionation and by disequilibrium fractionation during supercooling. Here we use combined electron probe microanalysis, isotopography, transmission electron microscopy and selected area electron diffraction to show that crystal rims are significantly enriched in aluminium (up to c. 1 wt%) and hydrogen (up to c. 10 000 ppm) hosted in oriented low-density amorphous domains. These domains are interpreted to have formed by melting of deuteric and/or post-deuteric metasomatic alteration minerals upon uptake of older olivine crystals into fresh, initially aphyric host melts up to a few hours prior to eruption. It is argued that uptake of variably altered crystals into initially aphyric or sparsely phyric melts may be a common process at subduction zones, and can account for typical disequilibrium textures displayed by arc magmas erupted in SW Japan and elsewhere. Analyses of the altered crystal cargo in arc volcanic rocks therefore provides an important tool for understanding subvolcanic hydrothermal systems and the interaction of ascending melts with such systems.
  • Yoshihiko Matsui, Asuka Sakamoto, Soichi Nakao, Takuma Taniguchi, Taku Matsushita, Nobutaka Shirasaki, Naoya Sakamoto, Hisayoshi Yurimoto
    Environmental science & technology 48 18 10897 - 903 2014年09月16日 [査読有り][通常論文]
     
    Decreasing the particle size of powdered activated carbon may enhance its equilibrium adsorption capacity for small molecules and micropollutants, such as 2-methylisoborneol (MIB) and geosmin, as well as for macromolecules and natural organic matter. Shell adsorption, in which adsorbates do not completely penetrate the adsorbent but instead preferentially adsorb near the outer surface of the adsorbent, may explain this enhancement in equilibrium adsorption capacity. Here, we used isotope microscopy and deuterium-doped MIB and geosmin to directly visualize the solid-phase adsorbate concentration profiles of MIB and geosmin in carbon particles. The deuterium/hydrogen ratio, which we used as an index of the solid-phase concentration of MIB and geosmin, was higher in the shell region than in the inner region of carbon particles. Solid-phase concentrations of MIB and geosmin obtained from the deuterium/hydrogen ratio roughly agreed with those predicted by shell adsorption model analyses of isotherm data. The direct visualization of the localization of micropollutant adsorbates in activated carbon particles provided direct evidence of shell adsorption.
  • Ai-Cheng Zhang, Shoichi Itoh, Naoya Sakamoto, Ru-Cheng Wang, Hisayoshi Yurimoto
    GEOCHIMICA ET COSMOCHIMICA ACTA 130 78 - 92 2014年04月 [査読有り][通常論文]
     
    Aluminum-rich chondrules are one of the most interesting components of primitive chondrites, because they have characteristics that are similar to both Ca, Al-rich inclusions (CAIs) and ferromagnesian chondrules. However, their precursor and formation history remain poorly constrained, especially with respect to their oxygen isotopic distributions. In this study, we report on the petrography, mineralogy, oxygen isotope ratios, and rare-earth-element compositions of a sapphirine-bearing Al-rich chondrule (SARC) in the ungrouped chondrite Dar al Gani (DaG) 978. The SARC has a complex core-mantlerim texture; while both the core and the mantle are mainly composed of Al-rich enstatite and anorthite with minor amounts of mesostasis, these regions are distinguished by the presence of Fe-rich spinel and sapphirine in the core and their absence in the mantle. The rim of the SARC consists mainly of Fe-rich olivine, enstatite, and Fe-Ni metal. Spinel and some olivine grains in the SARC are O-16-rich, with Delta O-17 values down to -20 parts per thousand and -23 parts per thousand, respectively. Enstatite, sapphirine, and most olivine grains have similar Delta O-17 values (similar to -7 parts per thousand), which are lower than those of anorthite and the mesostasis (including augite therein) (Delta O-17: similar to -3 parts per thousand). Mesostasis from both the core and mantle have Group II rare-earth-element (REE) patterns; however, the core mesostasis has higher REE concentrations than the mantle mesostasis. These observations provide a strong indication that the SARC formed by the melting and crystallization of a mixture of materials from Group II CAIs and ferromagnesian chondrules. Both spinel and olivine with O-16-rich features could be of relict origin. The O-16-poor isotopic compositions of most components in Al-rich chondrules can be explained by oxygen isotopic exchange between the melt and O-16-poor nebular gas (Delta O-17: similar to -7 parts per thousand) during melting in chondrule-forming regions; whereas the anorthite and mesostasis could have experienced further oxygen isotopic exchange with a relatively O-16-poor reservoir (Delta O-17: similar to -3 parts per thousand) on the parent body, likely during fluid-assisted thermal metamorphism. During the same thermal metamorphism event, spinel, olivine, some enstatite, and the mesostasis experienced Mg-Fe exchange to various extents. (C) 2013 Elsevier Ltd. All rights reserved.
  • Yukari Kuga, Naoya Sakamoto, Hisayoshi Yurimoto
    The New phytologist 202 2 594 - 605 2014年04月 [査読有り][通常論文]
     
    The objective of this study was to elucidate the transfer of nutrient elements in orchid symbiotic protocorms at the cellular level by imaging of stable isotope tracers. We address the long-standing question of whether nutrients move by transport across the symbiotic interface or solely by lysis of fungal pelotons. [U-(13) C]glucose and (15) NH4 (15) NO3 were added to Ceratobasidium sp. hyphae extending from symbiotic protocorms of Spiranthes sinensis. Isotope images were taken from resin-embedded sections of protocorms using ultra-high spatial resolution secondary ion mass spectrometry (SIMS). Analyses of regions of interest were conducted on isotope ratio images for fungal and host structures. Amyloplasts adjacent to young pelotons showed elevated (13) C/(12) C, which indicated that fungal carbon (C) was transferred from live hyphae. Senescent pelotons and their surrounding host cytoplasm showed significantly higher isotope ratios than young pelotons and surrounding host cytoplasm. These results indicate an inflow of C to senescent hyphae, which was then transferred to the host. The findings of this study provide some support for each of the two contradictory hypotheses concerning nutrient exchange in the symbiotic protocorm: the interface between the symbionts is involved before fungal senescence, and peloton degradation also releases a significant amount of C and nitrogen to host cells.
  • Georg F. Zellmer, Naoya Sakamoto, Yoshiyuki Iizuka, Masaya Miyoshi, Yoshihiko Tamura, Hui-Ho Hsieh, Hisayoshi Yurimoto
    Geological Society Special Publication 385 1 161 - 184 2014年 [査読有り][通常論文]
     
    Minerals of mafic rocks from theSWJapan arc have been studied to deduce P-T-XH2O conditions and their variations in mafic arc magmas. Two-pyroxene thermobarometry of magmas from several volcanoes yields constant temperatures and variable pressures. MELTS fractional crystallization modelling is employed to show that such 'pseudo-decompression paths' (PDPs) are artefacts that derive from uptake of pyroxene antecrysts formed at a range of crustal levels by isobaric cooling of previously intruded mafic melts. It is shown that PDPs can be used to constrain oxygen fugacities and initial water contents of the intruded magmas. These constraints, and plagioclase hygrometry, indicate that initial melt H2O contents change systematically along the SW Japan arc. Direct determination of hydrogen in olivine by secondary ion mass spectrometry yields consistently low olivine H2O contents of 11+4 ppm (1s), with little, if any, along-arc variations. MELTS modelling indicates that crystallization of calcic plagioclase and olivine dominantly occurs during upper crustal differentiation of mafic melts. The combined data indicate that aphyric melts are released from the mantle wedge, taking up most if not all crystals from previously intruded plutonic rocks during rapid magma ascent to the surface. © The Geological Society of London 2014.
  • Toshihiro Watanabe, Ran Kouho, Tomo Katayose, Nobuyuki Kitajima, Naoya Sakamoto, Noriko Yamaguchi, Takuro Shinano, Hisayoshi Yurimoto, Mitsuru Osaki
    Plant, cell & environment 37 1 45 - 53 2014年01月 [査読有り][通常論文]
     
    Low-molecular-weight thiol (LMWT) synthesis has been reported to be directly induced by arsenic (As) in Pteris vittata, an As hyperaccumulator. Sulphur (S) is a critical component of LMWTs. Here, the effect of As treatment on the uptake and distribution of S in P. vittata was investigated. In P. vittata grown under low S conditions, the presence of As in the growth medium enhanced the uptake of SO4(2-), which was used for LMWT synthesis in fronds. In contrast, As application did not affect SO4(2-) uptake in Nephrolepis exaltata, an As non-hyperaccumulator. Moreover, the isotope microscope system revealed that S absorbed with As accumulated locally in a vacuole-like organelle in epidermal cells, whereas S absorbed alone was distributed uniformly. These results suggest that S is involved in As transport and/or accumulation in P. vittata. X-ray absorption near-edge structure analysis revealed that the major As species in the fronds and roots of P. vittata were inorganic As(III) and As(V), respectively, and that As-LMWT complexes occurred as a minor species. Consequently, in case of As accumulation in P. vittata, S possibly acts as a temporary ligand for As in the form of LMWTs in intercellular and/or intracellular transport (e.g. vacuolar sequestration).
  • Minako Hashiguchi, Isao Sakaguchi, Naoya Sakamoto, Hisayoshi Yurimoto, Shunichi Hishita, Naoki Ohashi
    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 121 1420 1004 - 1007 2013年12月 [査読有り][通常論文]
     
    We studied the diffusion of Zn in dense SnO2 ceramics by using secondary ion mass spectrometry (SIMS). Dense SnO2 ceramics with additives of 6 mol.% MgO and 0.2 mol.% Sb2O5 were synthesized, and Zn was implanted in the SnO2 ceramics by ion implantation technique. The implanted samples were annealed at 850-1200 degrees C, and the concentration profiles of Zn were evaluated by SIMS. The temperature dependence of Zn diffusion at 850-950 degrees C could be expressed as D-Zn[cm(2)/s] = 3.3 x 10(6) exp(-463.5[kJ/mol]/RT). These results in relation to the fabrication process of SnO2 with added ZnO was then discussed. (C) 2013 The Ceramic Society of Japan. All rights reserved.
  • Isao Sakaguchi, Naoya Sakamoto, Minako Hashiguchi, Hisayoshi Yurimoto, Shunichi Hishita, Naoki Ohashi
    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 121 1419 956 - 959 2013年11月 [査読有り][通常論文]
     
    We investigated the effect of zinc oxide addition for the defects in the dense SnO2 ceramics. Cathode and photoluminescence properties revealed the luminescence originated to oxygen vacancies in SnO2 grains and the presence of non-radiative defect at the grain boundaries. The oxygen diffusion profile showed that the oxygen diffusion was controlled by the limited process at the surface and uniform concentration of O-18 at the grain boundaries inner side of sample. This sample exhibited a low Zn concentration in grains and a high Zn concentration at grain boundaries. We conclude that segregation of Zn at grain boundaries prevents SnO2 from decomposing at high temperatures, enabling dense SnO2 ceramics to be obtained. (C)2013 The Ceramic Society of Japan. All rights reserved.
  • Tomohiro Hamasaki, Takahiro Matsumoto, Naoya Sakamoto, Akiko Shimahara, Shiori Kato, Ayumi Yoshitake, Ayumi Utsunomiya, Hisayoshi Yurimoto, Esteban C Gabazza, Tadaaki Ohgi
    Nucleic acids research 41 12 e126  2013年07月 [査読有り][通常論文]
     
    Radioisotopes and fluorescent compounds are frequently used for RNA labeling but are unsuitable for clinical studies of RNA drugs because of the risk from radiation exposure or the nonequivalence arising from covalently attached fluorophores. Here, we report a practical phosphoramidite solid-phase synthesis of (18)O-labeled RNA that avoids these disadvantages, and we demonstrate its application to quantification and imaging. The synthesis involves the introduction of a nonbridging (18)O atom into the phosphate group during the oxidation step of the synthetic cycle by using (18)O water as the oxygen donor. The (18)O label in the RNA was stable at pH 3-8.5, while the physicochemical and biological properties of labeled and unlabeled short interfering RNA were indistinguishable by circular dichroism, melting temperature and RNA-interference activity. The (18)O/(16)O ratio as measured by isotope ratio mass spectrometry increased linearly with the concentration of (18)O-labeled RNA, and this technique was used to determine the blood concentration of (18)O-labeled RNA after administration to mice. (18)O-labeled RNA transfected into human A549 cells was visualized by isotope microscopy. The RNA was observed in foci in the cytoplasm around the nucleus, presumably corresponding to endosomes. These methodologies may be useful for kinetic and cellular-localization studies of RNA in basic and pharmaceutical studies.
  • Hiromi Kimura-Suda, Kyosuke Kanazawa, Sachio Kobayashi, Mieko Kuwahara, Teppei Ito, Naoya Sakamoto, Makoto Kajiwara, Hideyuki Yamato, Kuniharu Ijiro, Hisayoshi Yurimoto
    JOURNAL OF BONE AND MINERAL RESEARCH 28 2013年02月 [査読有り][通常論文]
  • Hiromi Kimura-Suda, Kajiwara Makoto, Sakamoto Naoya, Kobayashi Sachio, Ijiro Kuniharu, Yurimoto Hisayoshi, Yamato Hideyuki
    Journal of Oral Biosciences 55 2 61 - 65 2013年 [査読有り][通常論文]
     
    We describe the comprehensive analysis of bone quality by using the isotope microscopy, Fourier transform infrared (FTIR) imaging, and Raman spectroscopy, which are non-destructive techniques. Isotope microscopy is a novel tool for visualizing microdomains within materials through the imaging of the 3-dimensional distribution of isotopes. This technique enabled us to observe calcium metabolism in the tibiae of mice. Thus, a stable calcium isotope fed to mice was observed in the trabecular and cortical bones. FTIR and Raman spectroscopies are powerful tools for characterizing the chemical compositions of materials and provide both qualitative and quantitative information on molecular structure. An FTIR imaging system, which is an accessory for FTIR spectroscopy, provides a distribution map of functional components in the sample. The crystallinity, secondary structure of collagen, carbonate-to- phosphate ratio, and mineral-to-matrix ratio of bone can be obtained from the IR spectra extracted from the selected area of an FTIR image. Raman spectroscopy complements FTIR spectroscopy however, the Raman spectrum provides information about functional groups in a sample as well as its FTIR spectrum. The major advantage of Raman spectroscopy for bone analysis is the ability to obtain spectra with higher spatial resolution compared with those acquired using FTIR spectroscopy. Moreover, a wide range of samples, including aqueous solutions, fibers, powders, or frozen materials can be readily analyzed, without any special preparation. Raman spectroscopy generates data on crystallinity, carbonate-to-phosphate ratio, and mineral-to-matrix ratio in bone. © 2013 Japanese Association for Oral Biology.
  • Hiromi Hyodo, Azusa Terao, Jun Furukawa, Naoya Sakamoto, Hisayoshi Yurimoto, Shinobu Satoh, Hiroaki Iwai
    PloS one 8 11 e78949  2013年 [査読有り][通常論文]
     
    Fruit ripening is one of the developmental processes accompanying seed development. The tomato is a well-known model for studying fruit ripening and development, and the disassembly of primary cell walls and the middle lamella, such as through pectin de-methylesterified by pectin methylesterase (PE) and depolymerization by polygalacturonase (PG), is generally accepted to be one of the major changes that occur during ripening. Although many reports of the changes in pectin during tomato fruit ripening are focused on the relation to softening of the pericarp or the Blossom-end rot by calcium (Ca²⁺) deficiency disorder, the changes in pectin structure and localization in each tissues during tomato fruit ripening is not well known. In this study, to elucidate the tissue-specific role of pectin during fruit development and ripening, we examined gene expression, the enzymatic activities involved in pectin synthesis and depolymerisation in fruit using biochemical and immunohistochemical analyses, and uronic acids and calcium (Ca)-bound pectin were determined by secondary ion-microprobe mass spectrometry. These results show that changes in pectin properties during fruit development and ripening have tissue-specific patterns. In particular, differential control of pectin methyl-esterification occurs in each tissue. Variations in the cell walls of the pericarp are quite different from that of locular tissues. The Ca-binding pectin and hairy pectin in skin cell layers are important for intercellular and tissue-tissue adhesion. Maintenance of the globular form and softening of tomato fruit may be regulated by the arrangement of pectin structures in each tissue.
  • Satoko Motai, Takaya Nagai, Kohki Sowa, Tsuyoshi Watanabe, Naoya Sakamoto, Hisayoshi Yurimoto, Jun Kawano
    Journal of structural biology 180 3 389 - 93 2012年12月 [査読有り][通常論文]
     
    The skeletal texture and crystal morphology of the massive reef-building coral Porites lobata were observed from the nano- to micrometer scale using an analytical transmission electron microscope (ATEM). The skeletal texture consists of centers of calcification (COCs) and fiber area. Fiber areas contain bundles of needle-like aragonite crystals that are elongated along the crystallographic c-axis and are several hundred nanometers to one micrometer in width and several micrometers in length. The size distribution of aragonite crystals is relatively homogeneous in the fibers. Growth lines are observed sub-perpendicular to the direction of aragonite growth. These growth lines occur in 1-2 μm intervals and reflect a periodic contrast in the thickness of an ion-spattered sample and pass through the interior of some aragonite crystals. These observations suggest that the medium filled in the calcification space maintains a CaCO₃-supersaturated state during fiber growth and that a physical change occurs periodically during the aragonite crystals of the fiber area.
  • Changkun Park, Shigeyuki Wakaki, Naoya Sakamoto, Sachio Kobayashi, Hisayoshi Yurimoto
    METEORITICS & PLANETARY SCIENCE 47 12 2070 - 2083 2012年12月 [査読有り][通常論文]
     
    High-precision isotope imaging analyses of reversely zoned melilite crystals in the gehlenitic mantle of Type A CAI ON01 of the Allende carbonaceous chondrite reveal that there are four types of oxygen isotopic distributions within melilite single crystals: (1) uniform depletion of 16O (delta 18O similar to-10 parts per thousand), (2) uniform enrichment of 16O (delta 18O similar to-40 parts per thousand), (3) variations in isotopic composition from 16O-poor core to 16O-rich rim (delta 18O similar to -10 parts per thousand to -30 parts per thousand, -20 parts per thousand to -45 parts per thousand, and -10 parts per thousand to -35 parts per thousand) with decreasing akermanite content, and (4) 16O-poor composition (delta 18O = -10 parts per thousand) along the crystal rim. Hibonite, spinel, and perovskite grains are 16O-rich (d18O similar to -45 parts per thousand), and adjoin 16O-poor melilites. Gas-solid or gas-melt isotope exchange in the nebula is inconsistent with both the distinct oxygen isotopic compositions among the minerals and the reverse zoning of melilite. Fluid-rock interaction on the parent body resulted in 16O-poor compositions of limited areas near holes, cracks, or secondary phases, such as anorthite or grossular. We conclude that reversely zoned melilites mostly preserve the primary oxygen isotopic composition of either 16O-enriched or 16O-depleted gas from which they were condensed. The correlation between oxygen isotopic composition and akermanite content may indicate that oxygen isotopes of the solar nebula gas changed from 16O-poor to 16O-rich during melilite crystal growth. We suggest that the radial excursions of the inner edge of the protoplanetary disk gas simultaneously resulted in both the reverse zoning and oxygen isotopic variation of melilite, due to mixing of 16O-poor disk gas and 16O-rich coronal gas. Gas condensates aggregated to form the gehlenite mantle of the Type A CAI ON01.
  • Noriyuki Kawasaki, Naoya Sakamoto, Hisayoshi Yurimoto
    METEORITICS & PLANETARY SCIENCE 47 12 2084 - 2093 2012年12月 [査読有り][通常論文]
     
    Different oxygen isotopic reservoirs have been recognized in the early solar system. Fluffy type A Ca-Al-rich inclusions (CAIs) are believed to be direct condensates from a solar nebular gas, and therefore, have acquired oxygen from the solar nebula. Oxygen isotopic and chemical compositions of melilite crystals in a type A CAI from Efremovka CV3 chondrite were measured to reveal the temporal variation in oxygen isotopic composition of surrounding nebular gas during CAI formation. The CAI is constructed of two domains, each of which has a core-mantle structure. Reversely zoned melilite crystals were observed in both domains. Melilite crystals in one domain have a homogeneous 16O-poor composition on the carbonaceous chondrite anhydrous mineral (CCAM) line of delta 18O = 510 parts per thousand, which suggests that the domain was formed in a 16O-poor oxygen isotope reservoir of the solar nebula. In contrast, melilite crystals in the other domain have continuous variations in oxygen isotopic composition from 16O-rich (delta 18O = -40 parts per thousand) to 16O-poor (delta 18O = 0 parts per thousand) along the CCAM line. The oxygen isotopic composition tends to be more 16O-rich toward the domain rim, which suggests that the domain was formed in a variable oxygen isotope reservoir of the solar nebula. Each domain of the type A CAI has grown in distinct oxygen isotope reservoir of the solar nebula. After the domain formation, domains were accumulated together in the solar nebula to form a type A CAI.
  • Naoya Sakamoto, Satoshi Aoyama, Shoji Kawahito, Hisayoshi Yurimoto
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 7 076701  2012年07月 [査読有り][通常論文]
     
    We designed a new type of stacked complementary metal-oxide-semiconductor active pixel sensor (SCAPS) for charged particles with real-time readout and single-ion detection capabilities. Here we present the characteristics of a new imager, SCAPS-II, which implements a newly devised pixel structure of 504 x 504 pixels for high sensitivity and a noise-reduction mechanism with analog accumulation capabilities inside the column readout circuits. The sensitivity for ions was estimated to be 150 mu V/ion under 10 keV Si+ ion irradiation, which is 5 times greater than that of conventional SCAPS. The noise floor was at the 3 ion level without the noise-reduction mechanism at a frame rate of 0.16 s/frame. The noise reduction mechanism reduced the noise to the 1.7 ion level at 0.3 s/frame with 13 samplings. A combination of the noise-reduction mechanism and a multiple-frame-averaging technique achieved a noise level of 0.3 ions. Single-ion detectability was demonstrated using a combination of the noise-reduction mechanism and the multiple-frame-averaging technique that reduced the noise to the 0.3 ion level with 13 samplings, employing an integration circuit and 50-frame averaging at 14.4 s/frame. (C) 2012 The Japan Society of Applied Physics
  • Hisayoshi Yurimoto, Ken-ichi Abe, Masanao Abe, Mitsuru Ebihara, Akio Fujimura, Minako Hashiguchi, Ko Hashizume, Trevor R. Ireland, Shoichi Itoh, Juri Katayama, Chizu Kato, Junichiro Kawaguchi, Noriyuki Kawasaki, Fumio Kitajima, Sachio Kobayashi, Tatsuji Meike, Toshifumi Mukai, Keisuke Nagao, Tomoki Nakamura, Hiroshi Naraoka, Takaaki Noguchi, Ryuji Okazaki, Changkun Park, Naoya Sakamoto, Yusuke Seto, Masashi Takei, Akira Tsuchiyama, Masayuki Uesugi, Shigeyuki Wakaki, Toru Yada, Kosuke Yamamoto, Makoto Yoshikawa, Michael E. Zolensky
    SCIENCE 333 6046 1116 - 1119 2011年08月 [査読有り][通常論文]
     
    Meteorite studies suggest that each solar system object has a unique oxygen isotopic composition. Chondrites, the most primitive of meteorites, have been believed to be derived from asteroids, but oxygen isotopic compositions of asteroids themselves have not been established. We measured, using secondary ion mass spectrometry, oxygen isotopic compositions of rock particles from asteroid 25143 Itokawa returned by the Hayabusa spacecraft. Compositions of the particles are depleted in O-16 relative to terrestrial materials and indicate that Itokawa, an S-type asteroid, is one of the sources of the LL or L group of equilibrated ordinary chondrites. This is a direct oxygen-isotope link between chondrites and their parent asteroid.
  • James P. Greenwood, Shoichi Itoh, Naoya Sakamoto, Paul Warren, Lawrence Taylor, Hisayoshi Yurimoto
    NATURE GEOSCIENCE 4 2 79 - 82 2011年02月 [査読有り][通常論文]
     
    Water plays a critical role in the evolution of planetary bodies(1), and determination of the amount and sources of lunar water has profound implications for our understanding of the history of the Earth-Moon system. During the Apollo programme, the lunar samples were found to be devoid of indigenous water(2,3). The severe depletion of volatiles, including water, in lunar rock samples(4) has long been seen as strong support for the theory that the Moon formed during a giant impact event(5). Water has now been identified in lunar volcanic glasses(6) and apatite(7-9), but the sources of water to the Moon have not been determined. Here we report ion microprobe measurements of water and hydrogen isotopes in the hydrous mineral apatite, derived from crystalline lunar mare basalts and highlands rocks collected during the Apollo missions. We find significant water in apatite from both mare and highlands rocks, indicating a role for water during all phases of the Moon's magmatic history. Variations of hydrogen isotope ratios in apatite suggest sources for water in lunar rocks could come from the lunar mantle, solar wind protons and comets. We conclude that a significant delivery of cometary water to the Earth-Moon system occurred shortly after the Moon-forming impact.
  • Yamamoto, K, Sakamoto, N, Yurimoto, H
    SURFACE AND INTERFACE ANALYSIS 42 10-11 1603 - 1605 2010年10月 [査読有り][通常論文]
     
    By analyzing the noise characteristics of a stacked CMOS-type active pixel sensor (SCAPS), we developed a noise reduction method. We also developed a multiple frame-averaging method based on a correlated double sampling (CDS) between averaged frames, which use the multiple frames collected by nondestructive readout of signals before and after ion irradiation. This method suppresses SCAPS read noise to 11 mu V, corresponding to 0.37 ions. Ion transfer and noise performance were evaluated by above method, leading to the confirmation of noise suppression below the level of single ion detection and the expansion of the dynamic range of SCAPS to 102 dB. Copyright (C) 2010 John Wiley & Sons, Ltd.
  • James P. Greenwood, Shoichi Itoh, Naoya Sakamoto, Paul H. Warren, Lawrence A. Taylor, Hisayoshi Yurimoto
    GEOCHIMICA ET COSMOCHIMICA ACTA 74 12 A354 - A354 2010年06月 [査読有り][通常論文]
  • Sakamoto Naoya, Itoh Shoichi, Yurimoto Hisayoshi
    APPLIED SURFACE SCIENCE 255 4 1458 - 1460 2008年12月15日 [査読有り][通常論文]
     
    We report a discovery of a chemically and isotopically unique material distributed ubiquitously in fine-grained matrix of a primitive carbonaceous chondrite Acfer 094. The observations were made in situ using a novel high precision imaging technique adopted direct-imaging method. The material is extremely enriched in heavy oxygen isotopes of O-17 and O-18 of +18% relative to the Earth's ocean while previously reported variation of oxygen isotopes is as large as a range from -8% to 0%. Based on the unique chemical composition of the material, the abundance of the material in the meteorite matrix is calculated to be 94 +/- 20 ppm (sigma) by volume using elemental mapping with a 7 mu m(2) spatial resolution by FE-SEM-EDS on the meteorite thin section. The average size of identified materials is 5 mu m x 5 mu m x 5 mu m. Therefore, isotope imaging capability over 500 mu m x 500 mu m area with micron resolution and an isotopic ratio precision of 1% is required to investigate about the presence of such material. (C) 2008 Elsevier B. V. All rights reserved.
  • Yusuke Seto, Naoya Sakamoto, Kiyoshi Fujino, Takashi Kaito, Tetsuo Oikawa, Hisayoshi Yurimoto
    GEOCHIMICA ET COSMOCHIMICA ACTA 72 11 2723 - 2734 2008年06月 [査読有り][通常論文]
     
    We report the mineral compositions and micro-texture of the isotopically anomalous (delta(17,18)O(SMOW) similar to + 180 parts per thousand) Fe-S-Ni-O material recently discovered in matrix of the primitive carbonaccous chondrite Acfer 094 [Sakamoto N., Seto Y., Itoh S., Kuramoto K., Fujino K., Nagashima K., Krot A. N. and Yurimoto H. (2007) Oxygen isotope evidence for remnants of the early solar system primordial water. Science 317, 231-233]. Synchrotron radiation X-ray diffraction and transmission electron microscopy studies indicate that this material consists of the symplectitically intergrown magnetite (Fe(3)O(4)) and pentlandite (Fe(5.7)Ni(3.3)S(8)) with magnetite/pentlandite volume ratio of similar to 2.3. Magnetite forms column-shaped grains (10-30 nm in diameter and 100-200 nm in length); pentlandite occurs as worm-shaped grains or aggregates of grains 100-300 nm in size between magnetite crystals. Although both the X-ray diffraction and electron energy loss spectra support identification of iron oxide as magnetite, the electron diffraction patterns show that magnetite has a weak 3-fold superstructure, possibly due to ordering of vacancies. We infer that the isotopically anomalous symplectite formed by sulfurization and oxidization of metal grains either in the solar nebula or on an icy planetesimal. The intersite cation distribution of pentlandite suggests that time-scale of oxidation was no longer than 1000 years. (C) 2008 Elsevier Ltd. All rights reserved.
  • A. N. Krot, M. Chaussidon, H. Yurimoto, N. Sakamoto, K. Nagashima, I. D. Hutcheon, G. J. MacPherson
    GEOCHIMICA ET COSMOCHIMICA ACTA 72 10 2534 - 2555 2008年05月 [査読有り][通常論文]
     
    In situ oxygen isotopic measurements of primary and secondary minerals in Type C CAIs from the Allende CV3 chondrite reveal that the pattern of relative enrichments and depletions of O-16 in the primary minerals within each individual CAI are similar to the patterns observed in Types A and B CAIs from the same meteorite. Spinet is consistently the most O-16-rich (Delta O-17 = -25 parts per thousand to -15 parts per thousand), followed by Al,Ti-dioside (Delta O-17 = -20 parts per thousand to -5 parts per thousand) and anorthite (Delta O-17 = - 15 parts per thousand to 0 parts per thousand). Melilite is the most O-16-depleted primary mineral (Delta O-17 = -5 parts per thousand to -3 parts per thousand). We conclude that the original melting event that formed Type C CAIs occurred in a O-16-rich (Delta O-17 <= 20 parts per thousand) nebular gas and they subsequently experienced oxygen isotopic exchange in a O-16-poor reservoir. At least three of these (ABC, TS26F1 and 93) experienced remelting at the time and place where chondrules were forming, trapping and partially assimilating O-16-poor chondrule fragments. The observation that the pyroxene is O-16-rich relative to the feldspar, even though the feldspar preceded it in the igneous crystallization sequence, disproves the class of CAI isotopic exchange models in which partial melting of a O-16-rich solid in a O-16-poor gas is followed by slow crystallization in that gas. For the typical (not associated with chondrule materials) Type C CAIs as well for as the Types A and B CAIs, the exchange that produced internal isotopic heterogeneity within each CAI must have occurred largely in the solid state. The secondary phases grossular, monticellite and forsterite commonly have similar oxygen isotopic compositions to the melilite and anorthite they replace, but in one case (CAI 160) grossular is O-16-enriched (Delta O-17 = -10 parts per thousand to -6 parts per thousand) relative to melilite (Delta O-17 = -5 parts per thousand to -3 parts per thousand), meaning that the melilite and anorthite must have exchanged its oxygen subsequent to secondary alteration. This isotopic exchange in melilite and anorthite likely occurred on the CV parent asteroid, possibly during fluid-assisted thermal metamorphism. (C) 2008 Elsevier Ltd. All rights reserved.
  • A. N. Krot, M. Chaussidon, H. Yurimoto, N. Sakamoto, K. Nagashima, I. D. Hutcheon, G. J. MacPherson
    GEOCHIMICA ET COSMOCHIMICA ACTA 72 10 2534 - 2555 2008年05月 [査読有り][通常論文]
     
    In situ oxygen isotopic measurements of primary and secondary minerals in Type C CAIs from the Allende CV3 chondrite reveal that the pattern of relative enrichments and depletions of O-16 in the primary minerals within each individual CAI are similar to the patterns observed in Types A and B CAIs from the same meteorite. Spinet is consistently the most O-16-rich (Delta O-17 = -25 parts per thousand to -15 parts per thousand), followed by Al,Ti-dioside (Delta O-17 = -20 parts per thousand to -5 parts per thousand) and anorthite (Delta O-17 = - 15 parts per thousand to 0 parts per thousand). Melilite is the most O-16-depleted primary mineral (Delta O-17 = -5 parts per thousand to -3 parts per thousand). We conclude that the original melting event that formed Type C CAIs occurred in a O-16-rich (Delta O-17 <= 20 parts per thousand) nebular gas and they subsequently experienced oxygen isotopic exchange in a O-16-poor reservoir. At least three of these (ABC, TS26F1 and 93) experienced remelting at the time and place where chondrules were forming, trapping and partially assimilating O-16-poor chondrule fragments. The observation that the pyroxene is O-16-rich relative to the feldspar, even though the feldspar preceded it in the igneous crystallization sequence, disproves the class of CAI isotopic exchange models in which partial melting of a O-16-rich solid in a O-16-poor gas is followed by slow crystallization in that gas. For the typical (not associated with chondrule materials) Type C CAIs as well for as the Types A and B CAIs, the exchange that produced internal isotopic heterogeneity within each CAI must have occurred largely in the solid state. The secondary phases grossular, monticellite and forsterite commonly have similar oxygen isotopic compositions to the melilite and anorthite they replace, but in one case (CAI 160) grossular is O-16-enriched (Delta O-17 = -10 parts per thousand to -6 parts per thousand) relative to melilite (Delta O-17 = -5 parts per thousand to -3 parts per thousand), meaning that the melilite and anorthite must have exchanged its oxygen subsequent to secondary alteration. This isotopic exchange in melilite and anorthite likely occurred on the CV parent asteroid, possibly during fluid-assisted thermal metamorphism. (C) 2008 Elsevier Ltd. All rights reserved.
  • James P. Greenwood, Shoichi Itoh, Naoya Sakamoto, Edward P. Vicenzi, Hisayoshi Yurimoto
    GEOPHYSICAL RESEARCH LETTERS 35 5 2008年03月 [査読有り][通常論文]
     
    The high D/H of the Martian atmosphere (similar to 5-6 x terrestrial) is considered strong evidence for the loss of Martian water to space. The timing and magnitude of the loss of water from Mars can be constrained by measurements of D/H in Martian meteorites. Previous studies of Martian meteorites have shown a large range in D/H, from terrestrial values to as high as the current Martian atmosphere. Here we show that the ancient (similar to 4 Ga) Mars meteorite ALH84001 has a D/H 4 x terrestrial and that the young (similar to 0.17 Ga) Shergotty meteorite has a D/H 5.6 x terrestrial. We also find that the young Los Angeles shergottite has zoning in D/H that can be correlated to igneous growth zoning, strongly suggesting assimilation of D-enriched water during igneous crystallization near the Martian surface. In contrast to previous studies, we find higher and less variable D/H ratios in these three meteorites. Our results suggest a two-stage evolution for Martian water-a significant early loss of water to space (prior to 3.9 Ga) followed by only modest loss to space in the last 4 billion years. The current Martian atmospheric D/H has remained essentially unchanged for the last 165 Ma.
  • Naoya Sakamoto, Yusuke Seto, Shoichi Itoh, Kiyoshi Kuramoto, Kiyoshi Fujino, Kazuhide Nagashima, Alexander N Krot, Hisayoshi Yurimoto
    Science (New York, N.Y.) 317 5835 231 - 3 2007年07月13日 [査読有り][通常論文]
     
    Oxygen isotopic composition of our solar system is believed to have resulted from mixing of two isotopically distinct nebular reservoirs, 16O-rich and (17,18)O-rich relative to Earth. The nature and composition of the (17,18)O-rich reservoir are poorly constrained. We report an in situ discovery of a chemically and isotopically unique material distributed ubiquitously in fine-grained matrix of a primitive carbonaceous chondrite Acfer 094. This material formed by oxidation of Fe,Ni-metal and sulfides by water either in the solar nebula or on a planetesimal. Oxygen isotopic composition of this material indicates that the water was highly enriched in 17O and 18O (delta(17,18)O(SMOW) = +180 per thousand per mil), providing the first evidence for an extremely (17,18)O-rich reservoir in the early solar system.
  • Naoya Sakamoto, Hisayoshi Yurimoto
    SURFACE AND INTERFACE ANALYSIS 38 12-13 1760 - 1762 2006年12月 [査読有り][通常論文]
     
    A direct ion imaging system with single ion detection and high-precision imaging modes has been developed. This system is composed of a movable microchannel plate unit and a stacked CMOS-type active pixel sensor (SCAPS). Capabilities of single ion detection were evaluated by ion irradiations using secondary ion mass spectrometry. The experiment shows that this system accurately detected single incident ions. Copyright (C) 2006 John Wiley & Sons, Ltd.

その他活動・業績

  • 同位体顕微鏡で探る太陽系
    坂本直哉 日立ハイテク Scientific Instruments News 64 (2) 1 -7 2021年06月 [査読無し]
  • 川崎教行, 伊藤正一, 坂本直哉, SIMON Steven B., 圦本尚義, 圦本尚義 日本地球惑星科学連合大会予稿集(Web) 2020 2020年
  • 柿澤翔, 柿澤翔, 井上徹, 井上徹, 井上徹, 阿部遼太郎, 黒田みなみ, 黒田みなみ, 坂本直哉, 圦本尚義, 圦本尚義, 圦本尚義 日本地球化学会年会要旨集(Web) 66th 2019年
  • 川崎教行, 和田壮平, PARK C., 坂本直哉, 圦本尚義, 圦本尚義 日本地球化学会年会要旨集(Web) 66th 2019年
  • 川崎教行, PARK Changkun, 坂本直哉, 圦本尚義, 圦本尚義 日本地球惑星科学連合大会予稿集(Web) 2019 2019年
  • 磯野雄生, 坂本直哉, 圦本尚義 日本地球惑星科学連合大会予稿集(Web) 2019 2019年
  • 坂本直哉, 阿部光太郎, 圦本尚義 実験医学 36 (20) 3426‐3427 2018年12月15日 [査読無し][通常論文]
  • 坂本直哉, 槇納好岐, 川崎教行 日本地球惑星科学連合大会予稿集(Web) 2018 2018年
  • 久我ゆかり, WU Ting-Di, WU Ting-Di, 永田康祐, 坂本直哉, GUERQUIN-KERN Jean-Luc, GUERQUIN-KERN Jean-Luc, 勝山千恵, 圦本尚義 日本土壌微生物学会講演要旨集 2018 2018年
  • 柿澤翔, 井上徹, 井上徹, 井上徹, 阿部綾太郎, 黒田みなみ, 坂本直哉, 圦本尚義, 圦本尚義, 圦本尚義 高圧討論会講演要旨集 59th 2018年
  • 野々山貴行, 鈴木裕貴, 木山竜二, WANG Lei, 津田真寿美, 安田和則, 田中伸哉, 永田康祐, 藤田龍介, 坂本直哉, 圦本尚義, GONG Jian Ping 日本セラミックス協会秋季シンポジウム講演予稿集(CD-ROM) 31st 2018年
  • 黒田みなみ, 橘省吾, 坂本直哉, 圦本尚義, 圦本尚義 日本地球惑星科学連合大会予稿集(Web) 2018 2018年
  • 川崎教行, PARK Changkun, 坂本直哉, PARK Sun Young, KIM Hyun Na, 黒田みなみ, 圦本尚義, 圦本尚義 日本地球惑星科学連合大会予稿集(Web) 2018 2018年
  • 山本大貴, 黒田みなみ, 橘省吾, 橘省吾, 坂本直哉, 圦本尚義, 圦本尚義 日本地球惑星科学連合大会予稿集(Web) 2018 2018年
  • 黒田みなみ, 橘省吾, 坂本直哉, 圦本尚義 日本鉱物科学会年会講演要旨(Web) 2017 2017年
  • 久我 ゆかり, Ting-Di Wu, Jean-Luc Guerquin-Kern, 永田 康祐, 坂本 直哉, 圦本 尚義, 勝山 千恵 日本菌学会大会講演要旨集 61 (0) 109 -109 2017年 [査読無し][通常論文]
  • 川崎教行, SIMON Steven B, GROSSMAN Lawrence, 坂本直哉, 圦本尚義, 圦本尚義 日本地球惑星科学連合大会予稿集(Web) 2017 ROMBUNNO.PPS10‐29 (WEB ONLY) 2017年 [査読無し][通常論文]
  • T. Noguchi, H. Yabuta, S. Itoh, N. Sakamoto, T. Mitsunari, A. Okubo, R. Okazaki, T. Nakamura, S. Tachibana, K. Terada, M. Ebihara, N. Imae, M. Kimura, H. Nagahara METEORITICS & PLANETARY SCIENCE 51 A489 -A489 2016年08月 [査読無し][通常論文]
  • 久我ゆかり, 山田博之, 田代智子, 勝山千恵, 中村仁, 坂本直哉, 圦本尚義 日本土壌微生物学会講演要旨集 2016 9 2016年06月06日 [査読無し][通常論文]
  • 川崎教行, 伊藤正一, 坂本直哉, 圦本尚義, 圦本尚義 日本地球惑星科学連合大会予稿集(Web) 2016 ROMBUNNO.PPS12‐04 (WEB ONLY) 2016年 [査読無し][通常論文]
  • 黒田みなみ, 橘省吾, 奥村聡, 中村美千彦, 坂本直哉, 圦本尚義 日本鉱物科学会年会講演要旨集 2015 5 2015年09月18日 [査読無し][通常論文]
  • N. Kawasaki, N. Sakamoto, H. Yurimoto METEORITICS & PLANETARY SCIENCE 50 2015年08月 [査読無し][通常論文]
  • J. Bollard, N. Kawasaki, N. Sakamoto, K. Larsen, D. Wielandt, M. Schiller, J. Connelly, H. Yurimoto, M. Bizzarro METEORITICS & PLANETARY SCIENCE 50 2015年08月 [査読無し][通常論文]
  • 山本淳博, 川崎教行, 坂本直哉, 圦本尚義 日本地球惑星科学連合大会予稿集(Web) 2015 ROMBUNNO.PPS22‐12 (WEB ONLY) 2015年 [査読無し][通常論文]
  • 芳野極, 櫻井萌, 坂本直哉, 圦本尚義 高圧討論会講演要旨集 55th 6 2014年11月10日 [査読無し][通常論文]
  • 久我ゆかり, 坂本直哉, 圦本尚義 日本土壌肥料学会講演要旨集 60 36 2014年09月09日 [査読無し][通常論文]
  • C. Park, K. Nagashima, S. Wakaki, N. Sakamoto, S. Kobayashi, H. Yurimoto METEORITICS & PLANETARY SCIENCE 49 A315 -A315 2014年09月 [査読無し][通常論文]
  • 小笠原希実, 坂本直哉, 伊藤利章, 内藤哲, 高野順平, 圦本尚義 日本顕微鏡学会関東支部講演会予稿集 38th 41 2014年03月08日 [査読無し][通常論文]
  • 久我 ゆかり, 坂本 直哉, 圦本 尚義 土と微生物 68 (1) 36 -36 2014年 [査読無し][通常論文]
  • 小笠原希実, 坂本直哉, 伊藤利章, 圦本尚義, 内藤哲, 高野順平 日本植物学会大会研究発表記録 77th 167 2013年08月20日 [査読無し][通常論文]
  • 久我ゆかり, 坂本直哉, 圦本尚義 日本土壌微生物学会講演要旨集 2013 23 2013年06月19日 [査読無し][通常論文]
  • 小笠原希実, 坂本直哉, 伊藤利章, 圦本尚義, 内藤哲, 高野順平 日本植物生理学会年会要旨集 54th 335 2013年03月14日 [査読無し][通常論文]
  • 北村 啓太朗, 海野 進, 金山 恭子, 石塚 治, 坂本 直哉, 圦本 尚義 日本火山学会講演予稿集 2013 (0) 91 -91 2013年 [査読無し][通常論文]
  • H. Yabuta, S. Itoh, T. Noguchi, N. Sakamoto, M. Hashiguchi, K. Abe, S. Tsujimoto, D. Kilcoyne, A. Okubo, R. Okazaki, S. Tachibana, K. Terada, T. Nakamura, H. Nagahara METEORITICS & PLANETARY SCIENCE 47 A420 -A420 2012年07月 [査読無し][通常論文]
  • 圦本 尚義, 坂本 直哉 顕微鏡 = Microscopy 47 (2) 92 -97 2012年06月30日 [査読無し][通常論文]
     

    太陽系の起源の研究法として宇宙物質を実験室で分析する方法がある.宇宙物質は微細な組織を持っているため顕微鏡法が非常に有効な手段である.また,宇宙においては物質間の同位体組成の違いが顕著である場合が多いため,同位体は物質の起源や進化のトレーサーとして有効である.同位体は質量分析法により測定されるが微細構造を持つ物質には適用が限られていた.最近,同位体顕微鏡という装置が開発され質量分析法と顕微鏡法が融合した.それにより,同位体をトレーサーとして微細組織の形成を可視化し,解析できるようになった.本稿では,同位体顕微鏡により初めて明らかになった太陽系最古の物質,恒星の残骸物質,分子雲の氷の化石の研究について解説する.

  • 坂口勲, 坂本直哉, 圦本尚義, 大橋直樹, 菱田俊一 セラミックス基礎科学討論会講演要旨集 50th 21 2012年01月12日 [査読無し][通常論文]
  • Zhang Aicheng, 伊藤 正一, 坂本 直哉, 圦本 尚義, Wang Rucheng 日本地球化学会年会要旨集 59 (0) 269 -269 2012年 [査読無し][通常論文]
     
    We report mineralogy, oxygen isotopic and rare-earth-element compositions of a sapphirine-bearing Al-rich chondrule (SARC) from the Dar al Gani (DaG) 978 ungrouped carbonaceous chondrite. Our results indicate that the precursor of SARC included Group II CAIs as components. Assimilation of incompletely melted amoeboid olivine aggregate also occurred during formation of the ferromagnesian rim in SARC.
  • 圦本 尚義, 中村 智樹, 伊藤 正一, 坂本 直哉, 阿部 憲一, 橋口 未奈子, 片山 樹里, 加藤 千図, 川崎 教行, 小林 幸雄, 女池 竜二, 朴 昌根, 武井 将志, 若木 重行, 山本 広佑, 橋爪 光, 土山 明, 瀬戸 雄介, 長尾 敬介, 野口 高明, 海老原 充, 奈良岡 浩, 北島 富美雄, 岡崎 隆司, Ireland T.R., Zolensky M.E., 阿部 正真, 藤村 彰夫, 川口 淳一郎, 向井 利典, 上椙 真之, 矢田 達, 吉川 真 日本惑星科学会秋期講演会予稿集 2011 15 -15 2011年10月23日 [査読無し][通常論文]
  • 木村(須田)廣美, 梶原誠, 坂本直哉, 小林幸雄, 居城邦治, 圦本尚義, 大和英之 J Oral Biosci 53 (Supplement) 84 2011年09月01日 [査読無し][通常論文]
  • 木村 須田 廣美, 桑原 三恵子, 日高 公介, 金沢 恭祐, 本間 教嗣, 坂内 堅二, 菅野 三喜男, 梶原 誠, 大西 晃宏, 小林 幸雄, 坂本 直哉, 居城 邦治, 圦本 尚義, 大和 英之 バイオイメージング 20 (2) 95 -96 2011年08月10日 [査読無し][通常論文]
  • 女性研究者がリードするバイオイメージング 赤外イメージングおよび元素イメージングによる生体組織の解析
    木村 廣美, 須田, 桑原 三恵子, 日高 公介, 金沢 恭祐, 本間 教嗣, 坂内 堅二, 菅野 三喜男, 梶原 誠, 大西 晃宏, 小林 幸雄, 坂本 直哉, 居城 邦治, 圦本 尚義, 大和 英之 バイオイメージング 20 (2) 95 -96 2011年08月 [査読無し][通常論文]
  • 圦本 尚義, 中村 智樹, 野口 高明, 長尾 敬介, 海老原 充, 奈良岡 浩, 岡崎 隆一, 北島 富美雄, 向井 利典, 藤村 彰夫, 安部 正真, 伊藤 正一, 矢田 達, 上椙 真之, 吉川 真, 川口 淳一郎, 坂本 直哉, 小林 幸雄, 橋爪 光, 土`山 明, 瀬戸 雄介, T. R. Ireland, M. Zolensky 日本地球化学会年会要旨集 58 (0) 171 -171 2011年 [査読無し][通常論文]
     
    太陽系形成期の研究は,主に隕石を参照することにより検証がおこなわれ,進展して来た.隕石は小惑星の破片であるといわれているが,母天体となる小惑星が確認されている隕石は一つもない.小惑星イトカワにタッチダウンした惑星探査機はやぶさが,昨年,小惑星イトカワの表面物質を地球に持ち帰った.採取された試料は,最大で数百ミクロンの微粒子であるが,これらの試料を分析することにより,小惑星と隕石との関係の一部が初めて明らかになっていくことが期待される. 本講演では,酸素同位体組成,マグネシウム同位体組成戸26Al,微量元素組成について報告する.
  • 川崎 教行, 坂本 直哉, 圦本 尚義 日本地球化学会年会要旨集 58 (0) 178 -178 2011年 [査読無し][通常論文]
     
    本研究では,エフレモフカCV3コンドライト中のFluffy Type A CAIの岩石学的記載と,累帯構造を持つメリライト結晶の固溶体組成および酸素同位体組成の分析を行った.本CAIは,内部にWark-Loveringリムの断片のような構造があり,領域によって岩石学的特徴が異なることから,大きく4つのドメインに分類できる.各ドメインはその構造,鉱物組合せなどが異なり,特に2つのドメインのメリライトの固溶体組成と酸素同位体組成に違いが見られた.各ドメインの境界は大部分はWark-Loveringリムやその断片のような構造で区切られており,各ドメインは別々に形成され集合したものであると考えられる.
  • 阿部憲一, 坂本直哉, 圦本尚義 日本惑星科学会誌 遊・星・人 19 (4) 268 -272 2010年12月25日 [査読無し][通常論文]
  • 阿部 憲一, 坂本 直哉, 圦本 尚義 遊・星・人 : 日本惑星科学会誌 19 (4) 268 -272 2010年12月25日 [査読無し][通常論文]
     
    <特集>初期太陽系物質科学の最前線
  • 瀬戸 雄介, 藤 昇一, 坂本 直哉, 圦本 尚義 日本鉱物科学会年会講演要旨集 2010 157 -157 2010年09月23日 [査読無し][通常論文]
  • 甕 聡子, 永井 隆哉, 岨 康輝, 渡邊 剛, 坂本 直哉, 圦本 尚義 日本鉱物科学会年会講演要旨集 2010 84 -84 2010年09月23日 [査読無し][通常論文]
  • 山本広佑, 坂本直哉, 西尾崇, 居城邦治, 圦本尚義 日本分析化学会年会講演要旨集 59th 168 2010年09月01日 [査読無し][通常論文]
  • 木村(須田)廣美, 梶原誠, 坂本直哉, 小林幸雄, 居城邦治, 圦本尚義, 大和英之 高分子学会予稿集(CD-ROM) 59 (2 Disk1) ROMBUNNO.2PE123 2010年09月01日 [査読無し][通常論文]
  • J. P. Greenwood, S. Itoh, N. Sakamoto, E. P. Vicenzi, H. Yurimoto METEORITICS & PLANETARY SCIENCE 45 A68 -A68 2010年07月 [査読無し][通常論文]
  • 小林 幸雄, 永島 一秀, 殿谷 梓, 坂本 直哉, 伊藤 正一, RUSSELL S. S., KROT Alexander N., 圦本 尚義 日本鉱物科学会年会講演要旨集 2009 223 -223 2010年04月07日 [査読無し][通常論文]
  • 阿部 憲一, 坂本 直哉, 小島 秀康, KROT A. N., RUSSELL S. S., 圦本 尚義 日本鉱物科学会年会講演要旨集 2009 224 -224 2010年04月07日 [査読無し][通常論文]
  • 木村(須田)廣美, 梶原誠, 坂本直哉, 小林幸雄, 居城邦治, 圦本尚義, 大和英之 日本骨代謝学会学術集会プログラム抄録集 28th 163 2010年 [査読無し][通常論文]
  • K. Abe, N. Sakamoto, H. Kojima, A. N. Krot, H. Yurimoto METEORITICS & PLANETARY SCIENCE 44 A15 -A15 2009年07月 [査読無し][通常論文]
  • N. Sakamoto, S. Aoyama, S. Kawahito, H. Yurimoto METEORITICS & PLANETARY SCIENCE 44 A181 -A181 2009年07月 [査読無し][通常論文]
  • 坂本直哉 日本惑星科学会誌 遊・星・人 18 (1) 25 -30 2009年03月25日 [査読無し][通常論文]
     
    Acfer 094隕石中の磁鉄鉱(Fe_3O_4)と鉄ニッケル硫化物からなるユニークな微細結晶集合体が,太陽系物質で最も重い酸素同位体組成を持つことを発見した.熱力学計算により原始惑星系円盤における磁鉄鉱と硫化鉄の共存条件を求めたところ,この物質は太陽系星雲中では金属鉄または硫化鉄が重い酸素同位体組成を持つH_2Oと360K以下で反応して形成し,隕石母天体上で周囲のケイ酸塩との同位体交換が平衡に達していない事がわかった.このことから,太陽系の始原的な水が重い酸素同位体組成を持つことを示す.
  • 坂本 直哉 遊・星・人 : 日本惑星科学会誌 18 (1) 25 -30 2009年03月25日 [査読無し][通常論文]
     
    Acfer 094隕石中の磁鉄鉱(Fe_3O_4)と鉄ニッケル硫化物からなるユニークな微細結晶集合体が,太陽系物質で最も重い酸素同位体組成を持つことを発見した.熱力学計算により原始惑星系円盤における磁鉄鉱と硫化鉄の共存条件を求めたところ,この物質は太陽系星雲中では金属鉄または硫化鉄が重い酸素同位体組成を持つH_2Oと360K以下で反応して形成し,隕石母天体上で周囲のケイ酸塩との同位体交換が平衡に達していない事がわかった.このことから,太陽系の始原的な水が重い酸素同位体組成を持つことを示す.
  • 坂本 直哉, 青山 聡, 川人 祥二, 圦本 尚義 日本鉱物科学会年会講演要旨集 2009 (0) 230 -230 2009年 [査読無し][通常論文]
     
    リアルタイムにイオン検出可能な新しいイオンイメージャを開発している.このイメージャは25万個の独立したイオン検出器である画素から構成される.各画素のイオンに対する応答性は,画素キャパシタを小さくすることで従来の5倍となる150 µV/イオンに向上した.高速駆動時の読み出しノイズを低減するために,画素に蓄積した信号電荷を複数回サンプリングして積分することで相対的にノイズを低減する多重サンプリング機構を組み込み,16回積分した時の読み出しノイズは250 µV(1.7イオン相当)であった.イメージの読み出し速度は1回積分時で12.5フレーム/秒,16回積分時で8.3フレーム/秒を達成し,読み出しノイズは速度に依存しないことが分かった.全てのパラメータを最適化してノイズを低減できれば,リアルタイムにシングルイオンの検出が可能になると期待される.
  • Y. Seto, N. Sakamoto, K. Fujino, H. Yurimoto METEORITICS & PLANETARY SCIENCE 43 (7) A143 -A143 2008年07月 [査読無し][通常論文]
  • 瀬戸 雄介, 坂本 直哉, 藤野 清志, 圦本 尚義 日本鉱物科学会年会講演要旨集 2008 (0) 206 -206 2008年 [査読無し][通常論文]
     
    始原的炭素質コンドライトAcfer094のマトリックス中の酸素同位体異常物質"COS"について、放射光X線回折実験および透過電子顕微鏡観察から詳細な鉱物学的記載を行い、その生成条件を検討した。Ni含有量の高いもの(High-Ni COS)と低いもの(Low-Ni COS)を観察した結果、次のような相違点、類似点が見られた。(1)High-Ni COSはmagnetiteとpentlanditeから成るが、Low-Ni COSはmagnetiteとpyrrhotiteから成る。(2)High-Ni COSはmagnetiteとpentlanditeが入り組んだシンプレクタイトのような組織を示すが、Low-Ni COSは比較的等粒状のmagnetiteとpyrrhotiteの集合物である。(3)High-Ni COS中のmagnetiteは電子線回折において3倍周期の超構造を示すが、Low-Ni COS中のmagnetiteには超構造が見られない。(4) 両試料ともX線回折ではpentlanditeの明瞭な回折ピークが観察されるが、電子線では回折スポットが検出できない。いずれのCOSも酸化鉄と硫化鉄(+Ni)から構成されており、金属鉄(+Ni)の酸化・硫化による反応性生物である可能性が高い。High- / Low-Ni COSの組織、鉱物相の相違は、酸化・硫化反応以前のNi含有量の相違を反映していると考えられる。
  • 甕 聡子, 永井 隆哉, 坂本 直哉, 岨 康輝, 渡邊 剛, 圦本 尚義 日本鉱物科学会年会講演要旨集 2008 (0) 175 -175 2008年 [査読無し][通常論文]
     
    造礁性サンゴはアラゴナイトによってその骨格を形成し、その骨格に含まれる酸素同位体比、あるいは微量元素量が古環境復元に利用されている。例えば、アラゴナイト中のSr/Ca比の変動は、骨格形成時の海水温度と相関を持つとされ、過去の海水温度復元に用いられている。これは、骨格に含まれているSr(Porites sp.であれば約7000ppm)が全てアラゴナイトに固溶し、固溶割合の変動が鉱物生成時の温度の違いに起因するものであると考えられているからである。しかし、近年になりサンゴ骨格中にアラゴナイト以外の鉱物相の存在が示唆された。例えば、Greegor et al.(1997)はXANES、EXAFSを用いた実験で、Srの60%程度はアラゴナイト中に固溶しているが、残りの40%はアラゴナイト構造を持つSrCO3端成分として存在していると報告した。この報告が信頼できるとすると、Sr/Ca比を海水温度計として使うには注意が必要となる。一方Finch et al(2003a, 2003)は放射光を使ったmicro-EXAFSを用いての観察の結果、Srは全てアラゴナイト固溶体として存在するとGreegorとは異なった報告している。しかしながらいずれの報告もSrの配位環境やSr-O結合距離からの考察であり、これまで直接的な鉱物同定は行われていない。
  • 江端 新吾, 坂本 直哉, 圦本 尚義 日本地球化学会年会要旨集 55 (0) 375 -375 2008年 [査読無し][通常論文]
     
    プレソーラー粒子は太陽系形成以前に存在した太陽系を作る材料粒子であり、単独でマトリックス中に埋まっている。2007年江端らによってカンラン石や金属鉄とともにFeSで囲まれていたプレソーラーSiC粒子(SEC_ALH07)がEH3コンドライトから発見された。本研究では、周囲の組織の起源を解明する事を目的とし周囲を取り囲んでいるFeSの硫黄同位体組成分析を行った。‹BR›FeSの硫黄同位体組成は、δ‹SUP›33‹/SUP›S=-71±45‰, δ‹SUP›34‹/SUP›S=-48±56‰, δ‹SUP›36‹/SUP›S=27±173‰(誤差1σ)であった。δ‹SUP›34‹/SUB›S, δ‹SUP›36‹/SUP›Sの同位体組成は2 σの誤差内で太陽系の同位体組成と同じである事を示す。また、江端らの酸素同位体測定の報告によると内包されているカンラン石は太陽の同位体組成と同じであった。これらの結果は、周囲の硫化物はプレソーラーSiC粒子を核としてカンラン石や金属鉄と共に原始太陽系内において形成されたものである事を示唆する。
  • 瀬戸 雄介, 坂本 直哉, 圦本 尚義, 藤野 清志 日本鉱物学会・学術講演会,日本岩石鉱物鉱床学会学術講演会講演要旨集 2007 77 -77 2007年09月22日 [査読無し][通常論文]
  • N. Sakamoto, Y. Seto, S. Itoh, K. Kuramoto, K. Fujino, K. Nagashima, A. N. Krot, H. Yurimoto METEORITICS & PLANETARY SCIENCE 42 A134 -A134 2007年08月 [査読無し][通常論文]
  • Y. Seto, N. Sakamoto, K. Fujino, H. Yurimoto METEORITICS & PLANETARY SCIENCE 42 A140 -A140 2007年08月 [査読無し][通常論文]
  • 渡邊剛, 岨康輝, 坂本直哉, 圦本尚義 日本地球化学会年会講演要旨集 54th 239 2007年 [査読無し][通常論文]
  • 渡邊 剛, 岨 康輝, 坂本 直哉, 圦本 尚義 日本地球化学会年会要旨集 54 (0) 219 -219 2007年 [査読無し][通常論文]
     
    熱帯・亜熱帯域のサンゴ礁に生息する造礁性サンゴの骨格は、過去数百年間の環境変化が連続的に記録されており、環境変動を復元する強力なツールとして注目されてきた。サンゴ骨格のバイオミネラリゼーション(生物鉱化作用)はまだよく理解されておらず、まだこの問題の解明には石灰化が起こっている微小領域における生物地球化学的な情報が必要である。

共同研究・競争的資金等の研究課題

  • 水素の高ダイナミックレンジ定量イメージング
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2020年04月 -2024年03月 
    代表者 : 坂本 直哉
  • 骨代謝因子OPGが担う免疫寛容制御とカンジダ症の発症・増悪機序の解明
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2019年04月 -2022年03月 
    代表者 : 小林 美智代, 坂本 直哉, 奥村 一彦
  • 表面分析法による菌根における炭素・窒素・水素の細胞輸送と循環解析
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2017年04月 -2021年03月 
    代表者 : 久我 ゆかり, 勝山 千恵, 坂本 直哉, 長谷川 巧, 青柳 里果
     
    本研究は,植物と真菌の共生である菌根において、炭素、窒素、水素の共生者間-組織内輸送および環境との循環を、細胞小器官レベルでの局在解析手法を中心に明らかにすることを目的としている。 課題Ⅰ「表面分析法における試料調整法の影響評価」では,凍結試料を用いた安定同位体トレーサーの二次イオン質量分析法(SIMS)の開発に引き続き取り組んだ。高真空装置で凍結試料を測定するための,試料側の凍結法,表面作成法など,また,機械的な試料輸送・導入法,凍結ステージの開発はほぼ完成した。H30年度は特に,表面の導電性の改良に取り組み,測定法などの検討を行った。生細胞における安定同位体測定法の検討では,酵母をモデルとして用い,同位体標識リン酸を与えた真菌液胞内のポリリン酸の動態・分布を顕微ラマン散乱の手法を用いて明らかにすることを目指し,測定手法の確立に引き続き取り組んだ。本年度は,樹脂包埋試料作製における方法論の違いを検討するため,加圧凍結-凍結置換法の導入を検討した。 課題Ⅱ「同位体分子情報」では,アーバスキュラー菌根共生における宿主から渡される分子として推定される脂質および糖質の解析のため,TOF-SIMS法の導入に着手した。 課題Ⅲ「物質輸送と循環」では,アーバスキュラー菌根における物質輸送を同位体トレーサーの微細構造局在解析により明らかにするため,本研究で確立した同一試料を用いた透過型電子顕微鏡-SIMS法解析法を用い,分析を進めた。また,アーバスキュラー菌根における水輸送を解析するため,菌糸のみにトレーサーを与える培養系を確立した。土壌生態系における元素循環では,温度ストレスを与えた土壌中の菌糸圏微生物群(細菌および糸状菌)について,次世代シークエンサーを用いた群集構造解析を行った。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 橘 省吾, 三宅 亮, 坂本 直哉, 川野 潤
     
    宇宙鉱物学への応用をめざし,宇宙に主要に存在する鉱物であるフォルステライトの気相成長速度および異方性を原始惑星系円盤条件 (温度,圧力,ガス組成) を制御した実験で求める研究をおこなった.原始惑星系円盤でのフォルステライト形成条件に近い 1350 K,水素圧 5 Pa,水蒸気/水素比 0.05 を赤外線真空炉中に作成し,過飽和比 15-20 の条件でフォルステライトの気相成長の効率を表すパラメータ凝縮係数が 0.003-0.006 であることを決定した.
  • 日本学術振興会:科学研究費助成事業 若手研究(B)
    研究期間 : 2013年04月 -2015年03月 
    代表者 : 坂本 直哉
     
    隕石には,水質変質鉱物が含まれており,母天体の水の情報を保持していると考えられている.隕石の始原的構成物に含まれる鉄は元々酸素を含まないため,様々な条件で実験的に再現し隕石と比較することは初期太陽系の酸化還元状態を知る手掛かりとなると考えられる.本研究では,自動化した同位体顕微鏡システムによる酸素同位体イメージング手法を用いて,系統的にCMコンドライトに含まれる含水鉱物の酸素同位体分析を行い,含水鉱物間で酸素同位体組成が異なっている事が分かった.また,ソープションポンプを用いて同位体ドープ実験を行うシステムを構築した.
  • 日本学術振興会:科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2012年04月 -2013年03月 
    代表者 : 坂本 直哉
     
    細粒CAIの鉱物アイソクロンを求めるために必要な投影型二次イオン質量分析装置とイオンイメージセンサを用いた投影型同位体イメージングと高速なイオンイメージセンサの開発を行った.Mg存在度の大きく異なる複数鉱物を同一視野に含むMg同位体イメージの取得および150枚/秒でのイメージセンサの駆動に成功した.
  • 日本学術振興会:科学研究費助成事業 特別推進研究
    研究期間 : 2008年 -2012年 
    代表者 : 圦本 尚義, 橘 省吾, 伊藤 正一, 坂本 直哉, 大槻 かおり
     
    同位体顕微鏡による隕石の解剖学を実施し,隕石のいわゆる『解体新書』を作成した.その成果に基づき,太陽系創世時代とそれに直接つながる先太陽系時代の物質進化を解明し,物質に刻まれた証拠に立脚する宇宙における太陽系の特殊性と一般性を区分した新しい太陽系起源論を構築した.
  • 高感度同位体顕微鏡システムの開発と隕石への応用
    日本学術振興会:科学研究費助成事業 特別研究員奨励費
    研究期間 : 2007年 -2007年 
    代表者 : 坂本 直哉
     
    最近、申請者は同位体顕微鏡を用いて炭素質コンドライトAcfer 094から太陽系で最も17Oと18Oに富む物質を発見した。同位体顕微鏡とは、二次イオン質量分析装置と独自開発の二次元イオン検出器を組み合わせた、固体表面微小部分の同位体比変動の空間分布を分析可能な装置である。この物質の酸素同位体組成は、原始太陽系星雲の始源水を反映していると示唆されており、その存在の普遍性を調べることは初期太陽系形成時の物質進化を解明する上で重要である。本研究では、同位体顕微鏡を高感度化したシステムを開発することにより、他の隕石においてこの物質を迅速に探索することを目的としている。高感度化のために、検出器の蓄積信号を複数回読み出して平均化処理を行う読み出し方式を採用し、読み出しノイズxの低減を図った。その結果、読み出し回数に応じてノイズが低減され、この方式が有効であることを確認できた。また、信号強度が微弱な場合の読み出し方式を確立し、最適な読み出し回数を定式化した。これらの読み出し方式を最適化するための新しい制御システムを開発した。このシステムでは、必要な全てのモジュールが同一の工業用シャーシに格納され全てLabVIEWソフトェアで制御しており、駆動パルスの生成コードのVHDLからLabVIEWへの移植、駆動電圧の変更を容易にしたことにより柔軟な分析の最適化が可能となった。このシステムを同位体顕微鏡に取り付けて動作することを確認した。17Oと18Oに富む物質は磁鉄鉱と硫化鉄から構成されるが、Acfer 094には磁鉄鉱がほとんどない。 そこで、11種類の隕石について電界放出型電子顕微鏡を用いて観察し、各隕石に含まれる磁鉄鉱と硫化鉄の比率の違いから分析候補を選定する指標を得た。


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