Elsevier BV Acta Medica Okayama 0341-8162 269 2026 Aeolian dust provenance across the Eurasian Asian steppe from grain-size dependent quartz ƒΒ18O in surface soils 110109 EN Geer Teni Graduate School of Science and Technology, University of Tsukuba Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Maki Asano Faculty of Life and Environmental Sciences, University of Tsukuba Kenji Tamura Faculty of Life and Environmental Sciences, University of Tsukuba Aeolian dust from the Eurasian interior significantly impacts climate, ecosystems, and soil formation, but the role of the Eurasian steppe as a dust source remains uncertain. We present grain-size-sorted quartz ƒΒ18O values in topsoil at 24 sites across the Eurasian steppe, from Ukraine and Kazakhstan to Xinjiang, Mongolia, and Inner Mongolia. Quartz fractions were separated from four fine soil classes (<2, 2–10, 10–20, 20–50 ƒΚm) at all sites, with additional coarse classes (50–200, 200–500, 500–2000 ƒΚm) at lithologically distinct locations. Coarse quartz grains in the Mongolian–Inner Mongolian Highlands show a relatively low and narrow ƒΒ18O range (7.6–9.0ρ) over plutonic bedrocks and more variable higher values (8.9–17.8ρ) over sedimentary bedrocks, indicating dependence on local lithology. In contrast, fine quartz grains (2–50 ƒΚm) exhibit a ƒΒ18O trend independent of bedrock lithology, indicating the values of regionally homogenized dust components. The ƒΒ18O values of the finest quartz fractions, exhibiting the highest at each site, decreased from the Western Steppe Plain (19.0 } 0.8ρ) through the Central Upland Steppe (18.0 } 0.7ρ) to the Mongolian–Inner Mongolian Highlands (13.8 } 1.0ρ), reflecting the distal dust input. Comparison with published quartz ƒΒ18O values for Mongolian and Northern China deserts and East Asian soils suggests that variable mixtures of these steppe end-members with Gobi and northern Chinese desert sources, along different atmospheric pathways of the East Asian winter monsoon, mid-latitude westerlies, and subtropical jets, can explain the aerosol-sized quartz in Japan and Korea. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0016-7037 400 2025 Lithium- and oxygen-isotope compositions of a Si-rich nebular reservoir determined from chondrule constituents in the Sahara 97103 EH3 chondrite 51 71 EN Torii Douglas-Song The Pheasant Memorial Laboratory Institute for Planetary Materials, Okayama University Tsutomu Ota The Pheasant Memorial Laboratory Institute for Planetary Materials, Okayama University Masahiro Yamanaka The Pheasant Memorial Laboratory Institute for Planetary Materials, Okayama University Hiroshi Kitagawa The Pheasant Memorial Laboratory Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory Institute for Planetary Materials, Okayama University Christian Potiszil The Pheasant Memorial Laboratory Institute for Planetary Materials, Okayama University Tak Kunihiro The Pheasant Memorial Laboratory Institute for Planetary Materials, Okayama University Here we report the in situ ion-microprobe analyses of the Li- and O-isotope compositions of enstatite, FeO-rich pyroxene, olivine, glass, and cristobalite grains from six chondrule-related objects from the Sahara 97103 EH3 chondrite. The O-isotope composition of the enstatite grains scattered around the intersection between the terrestrial fractionation and primitive chondrule minerals lines. Whereas, that of olivine varied along the primitive chondrule minerals line. Based on the mineralogy, we found cristobalite formed as a result of Si saturation, instead of the reduction of FeO-rich silicates, consistent with Si-enrichment of whole rock enstatite chondrites. Based on the mineralogy and O-isotope compositions, we infer that olivines in some chondrules are relict grains. In chondrules that contained olivine, no abundant niningerite [(Mg,Fe,Mn)S] was observed. Thus, enstatite formation can be explained by the interaction of an olivine precursor with additional SiO2 (Mg2SiO4 + SiO2 ¨ Mg2Si2O6), instead of sulfidation (Mg2SiO4 + S ¨ 1/2 Mg2Si2O6 + MgS + 1/2 O2). Using the equation Mg2SiO4 + SiO2 ¨ Mg2Si2O6 and the O-isotope compositions of enstatite and olivine, the O-isotope composition of the additional SiO2 was estimated. Based on the O-isotope composition, we infer that there could be a Si-rich gas with an elevated ƒ’17O value similar to, or greater than the second trend line (ƒ’17O = 0.9 ρ) suggested by Weisberg et al. (2021), during chondrule formation. The variation in the Li-isotope compositions of enstatite and olivine grains from EH3 chondrules is smaller than that for the same phases from CV3 chondrules. The variation in the Li-isotope compositions of the enstatite and olivine grains from EH3 chondrules is also smaller than that of their O-isotope compositions. During the recycling of enstatite-chondrite chondrules, both Li- and O-isotope compositions were homogenized. Although enstatite is the major carrier of Li in EH3 chondrules, the Li-isotope composition (ƒΒ7Li) of enstatite is lower than that of whole rock EH3 chondrites, suggesting the existence of a phase with higher ƒΒ7Li. Meanwhile, the Li-isotope composition and concentration (ƒΒ7Li, [Li]) of enstatite is higher than that of olivine. The Li-isotope composition of the Si-rich gas was estimated to be ƒΒ7Li = 1 ρ, using a similar mass-balance calculation as applied for the O-isotope composition. The Li-isotope composition of the Si-rich gas from the enstatite-chondrite-chondrule forming-region, is consistent with that of whole rock EH3 chondrites, and differs significantly from that of the Si-rich gas from the carbonaceous-chondrite-chondrule forming-region (ƒΒ7Li = |11 ρ) determined by a previous study. We speculate that the Si-rich gas in the carbonaceous-chondrite-chondrule forming-region maintained the Li-isotope heterogeneity inherited from light lithium synthesized by galactic cosmic-ray spallation in the interstellar medium. No potential conflict of interest relevant to this article was reported.

Springer Science and Business Media LLC Acta Medica Okayama 2662-4435 6 1 2025 Biogeochemical impact of nickel and urea in the great oxidation event 654 EN Dilan M. Ratnayake The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University The Great Oxidation Event marks the first substantial increase in atmospheric oxygen on Earth. Despite the oxygenic photosynthesis that emerged hundreds of million years before this event, the specific biogeochemical mechanisms responsible for maintaining low oxygen levels for an extended period remain elusive. Here, we show the critical role of urea as a nitrogen source for cyanobacteria, the cascading impact of nickel on abiotic urea production, and their combined effects on the proliferation of cyanobacteria leading to the great oxidation event. Urea formation was experimentally evaluated under simulated Archean conditions and cyanobacterial growth was monitored providing urea as the nitrogen source. Our findings demonstrate that urea can be produced in the Archean cyanobacterial habitats with UV-C irradiation, shedding light on the controversy regarding the evolution of nitrogen-fixing enzymes in primitive cyanobacteria. We propose that environmental conditions in the early Archean, characterized by elevated urea and nickel concentration, may have hindered cyanobacterial expansion, contributing to the delay between the evolution of oxygenic photosynthesis and the onset of the great oxidation event. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0012-821X 653 2025 Meteoritic and asteroidal amino acid heterogeneity: Implications for planetesimal alteration conditions and sample return missions 119205 EN Christian Potiszil Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Tsutomu Ota Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Masahiro Yamanaka Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Katsura Kobayashi Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Ryoji Tanaka Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Eizo Nakamura Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Carbonaceous chondrites (CC) and asteroid return samples contain amino acids (AA), which are essential for an origin of life on the early Earth and can provide important information concerning planetesimal alteration processes. While many studies have investigated AA from CC, separate studies have often found differing abundances for the same meteorite. Accordingly, analytical bias, differing terrestrial contamination levels and intrinsic sample heterogeneity have been proposed as potential reasons. However, current analytical techniques allow for the analysis of several mg-sized samples and can thus enable an investigation of AA heterogeneity within single meteorite specimens. Here, such an analytical technique is applied to characterise the AA in triplicate aliquots of three CCs. The results indicate that CCs are heterogenous in terms of their AA at the mm-scale. Furthermore, the results help to further constrain the effects of planetesimal alteration on organic matter and the requirements of future sample return missions that aim to obtain organic-bearing extraterrestrial materials. No potential conflict of interest relevant to this article was reported.

American Astronomical Society Acta Medica Okayama 0004-637X 965 1 2024 Unraveling the Cr Isotopes of Ryugu: An Accurate Aqueous Alteration Age and the Least Thermally Processed Solar System Material 52 EN Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Dilan M. Ratnayake The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Tsutomu Ota The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Noah Miklusicak The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Tak Kunihiro The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Christian Potiszil The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Chie Sakaguchi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Katsura Kobayashi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Hiroshi Kitagawa The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Masahiro Yamanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Masanao Abe Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Akiko Miyazaki Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Aiko Nakato Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Satoru Nakazawa Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Masahiro Nishimura Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Tatsuaki Okada Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Takanao Saiki Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Satoshi Tanaka Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Fuyuto Terui Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Yuichi Tsuda Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Tomohiro Usui Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Sei-ichiro Watanabe Department of Earth and Planetary Sciences, Nagoya University Toru Yada Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Kasumi Yogata Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Makoto Yoshikawa Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University The analysis of samples returned from the C-type asteroid Ryugu has drastically advanced our knowledge of the evolution of early solar system materials. However, no consensus has been obtained on the chronological data, which is important for understanding the evolution of the asteroid Ryugu. Here, the aqueous alteration age of Ryugu particles was determined by the Mn–Cr method using bulk samples, yielding an age of 4.13 + 0.62/|0.55 Myr after the formation of Ca–Al-rich inclusions (CAI). The age corresponds to 4563.17 + 0.60/|0.67 Myr ago. The higher 55Mn/52Cr, ƒΓ54Cr, and initial ƒΓ53Cr values of the Ryugu samples relative to any carbonaceous chondrite samples implies that its progenitor body formed from the least thermally processed precursors in the outermost region of the protoplanetary disk. Despite accreting at different distances from the Sun, the hydrous asteroids (Ryugu and the parent bodies of CI, CM, CR, and ungrouped C2 meteorites) underwent aqueous alteration during a period of limited duration (3.8 } 1.8 Myr after CAI). These ages are identical to the crystallization age of the carbonaceous achondirtes NWA 6704/6693 within the error. The ƒΓ54Cr and initial ƒΓ53Cr values of Ryugu and NWA 6704/6693 are also identical, while they show distinct ƒ’'17O values. This suggests that the precursors that formed the progenitor bodies of Ryugu and NWA 6703/6693 were formed in close proximity and experienced a similar degree of thermal processing in the protosolar nebula. However, the progenitor body of Ryugu was formed by a higher ice/dust ratio, than NWA6703/6693, in the outer region of the protoplanetary disk. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0003-2670 1278 2023 Determination of mass-dependent chromium isotopic compositions in geological samples by double spike-total evaporation-thermal ionization mass spectrometry (DS-TE-TIMS) 341723 EN Dilan M. Ratnayake The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Background: Chromium isotopes have been used to trace geochemical and cosmochemical processes in the past. However, the presence of multivalent Cr species has made it difficult to isolate Cr from geological samples, particularly for samples with a low Cr mass fraction.<br> Results: Here, a simple three-step ion exchange chromatography procedure is presented to separate Cr from various sample matrices, ranging from ultramafic to felsic rocks. Throughout each of the column chromatography step, 1 mL of cation exchange resin AG50W-X8 (200–400 mesh) was used as the stationary phase and oxalic acid as a chelating agent, was used in addition to the inorganic acids. This method yielded high recoveries of Cr [93 } 8% (2SD, N = 7)] regardless of the lithology. The total procedural blank of Cr was <0.5 ng. We also developed a double spike-total evaporation-thermal ionization mass spectrometry (DS-TE-TIMS) technique that significantly reduced sample consumption to ∼20 ng of Cr per each measurement of mass-dependent 53Cr/52Cr.<br> Significance: This study achieved a 2SD external precision of 0.02ρ for the analysis of NIST NBS3112a and of 0.01–0.07ρ for the geological samples. This study enabled high-precision Cr isotope analysis in geological samples with various matrix and Cr compositions using relatively small sample volumes. No potential conflict of interest relevant to this article was reported.

Mary Ann Liebert Acta Medica Okayama 1531-1074 20 7 2020 The Albedo of Ryugu: Evidence for a High Organic Abundance, as Inferred from the Hayabusa2 Touchdown Maneuver 916 921 EN Christian Potiszil Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Katsura Kobayashi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Tak Kunihiro The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University The Hayabusa2 mission successfully collected samples from the asteroid Ryugu last year and will return these to Earth in December 2020. It is anticipated that the samples will enable the analysis of terrestrially uncontaminated organic matter and minerals. Such analyses are in turn expected to elucidate the evolution of organic matter through Solar System history, including the origination and processing of biogenically important molecules, which could have been utilized by the first organisms on Earth. In anticipation, studies have made predictions concerning the properties of Ryugu, including its composition. The spectral characteristics of Ryugu, such as albedo, have been employed to relate the asteroid to members of the carbonaceous chondrite group that have been identified on Earth. However, the recent Hayabusa2 touchdown highlights a disparity between the color of surfaces of displaced platy fragments, indicating a brightening trend for the surface exposed to space compared to that facing into the body. Here we present a mass balance calculation with reference to data from the literature, which indicates that Ryugu may contain a significantly higher abundance of organic matter (likely >50%) than the currently most accepted meteorite analogues. A high organic content may result in high levels of extractable organic matter for the second touchdown site, where the spacecraft sampled freshly exposed material. However, high abundances of insoluble aromatic/graphitic rich organic matter may be present in the first touchdown site, which sampled the surface of Ryugu that had been exposed to space. Moreover, we suggest that the potentially high organic abundance and the rubble-pile nature of Ryugu may originate from the capture of rocky debris by a comet nucleus and subsequent water-organic-mineral interactions and sublimation of water ice. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 0386-2208 95 4 2019 Hypervelocity collision and water-rock interaction in space preserved in the Chelyabinsk ordinary chondrite 165 177 EN Eizo Nakamura The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Tak Kunihiro The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Tsutomu Ota The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Chie Sakaguchi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Hiroshi Kitagawa Okayama Univ, Inst Planetary Mat, Pheast Mem Lab Geochem & Cosmochem Katsura Kobayashi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Masahiro Yamanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Yuri Shimaki The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Gray E. Bebout The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Hitoshi Miura Graduate School of Natural Sciences, Nagoya City University Tetsuo Yamamoto Institute of Low Temperature Science, Hokkaido University Vladimir Malkovets The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Victor Grokhovsky Institute of Physics and Technology, Ural Federal University Olga Koroleva Institute of Mineralogy, Ural Branch of the Russian Academy of Sciences South-Ural State University Konstantin Litasov V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences A comprehensive geochemical study of the Chelyabinsk meteorite reveals further details regarding its history of impact-related fragmentation and melting, and later aqueous alteration, during its transit toward Earth. We support an similar to 30 Ma age obtained by Ar-Ar method (Beard et al., 2014) for the impact-related melting, based on Rb-Sr isotope analyses of a melt domain. An irregularly shaped olivine with a distinct 0 isotope composition in a melt domain appears to be a fragment of a silicate-rich impactor. Hydrogen and Li concentrations and isotopic compositions, textures of Fe oxyhydroxides, and the presence of organic materials located in fractures, are together consistent with aqueous alteration, and this alteration could have pre-dated interaction with the Earth's atmosphere. As one model, we suggest that hypervelocity capture of the impact-related debris by a comet nucleus could have led to shock-wave-induced supercritical aqueous fluids dissolving the silicate, metallic, and organic matter, with later ice sublimation yielding a rocky rubble pile sampled by the meteorite. No potential conflict of interest relevant to this article was reported.

Oxford University Press Acta Medica Okayama 0022-3530 60 8 2019 Transition from Plume-driven to Plate-driven Magmatism in the Evolution of the Main Ethiopian Rift 1681 1715 EN Dejene Hailemariam Feyissa The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Hiroshi Kitagawa The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Tesfaye Demissie Bizuneh The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Kurkura Kabeto The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University New K-Ar ages, major and trace element concentrations, and Sr-Nd-Pb isotope data are presented for Oligocene to recent mafic volcanic rocks from the Ethiopian Plateau, the Main Ethiopian Rift (MER), and the Afar depression. Chronological and geochemical data from this study are combined with previously published datasets to reveal secular variations in magmatism throughout the entire Ethiopian volcanic region. The mafic lavas in these regions show variability in terms of silica-saturation (i.e. alkaline and sub-alkaline series) and extent of differentiation (mafic through intermediate to felsic). The P-T conditions of melting, estimated using the least differentiated basalts, reveal a secular decrease in the mantle potential temperature, from when the flood basalt magmas erupted (up to 1600 degrees C) to the time of the rift-related magmatism (<1500 degrees C). Variations in the Sr-Nd-Pb isotopic compositions of the mafic lavas can account for the involvement of multiple end-member components. The relative contributions of these end-member components vary in space and time owing to changes in the thermal condition of the asthenosphere and the thickness of the lithosphere. The evolution of the Ethiopian rift is caused by a transition from plume-driven to plate-driven mantle upwelling, although the present-day mantle beneath the MER and the Afar depression is still warmer than normal asthenosphere. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 03019268 334 2019 Tourmaline in a Mesoarchean pelagic hydrothermal system: Implications for the habitat of early life 105475 EN Tsutomu Ota Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Yuhei Aihara Department of Earth and Planetary Sciences, Kyushu University Shoichi Kiyokawa Department of Earth and Planetary Sciences, Kyushu University Ryoji Tanaka Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Eizo Nakamura The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University The RNA World hypothesis requires the synthesis of RNA to allow the emergence of life on Earth. Hydrothermal systems have been proposed as potential candidates for constructing complex biomolecules. However, in order to successfully form RNA, it is necessary to stabilize ribose, a RNA carbohydrate component. Borate has been found to stabilize ribose. Therefore, boron rich hydrothermal systems are important environments concerning the origin of life on Earth. <br/> The 3.2-Ga Dixon Island Formation of the West Pilbara Superterrane, Western Australia, is a volcano-sedimentary sequence. The Formation represents a Mesoarchean pelagic hydrothermal system, which formed adjacent to an immature island arc. Fine-grained tourmaline, in addition to biogenic carbonaceous matter and spherulitic and tubular bacteriomorphs, are found in black chert. A boron-rich environment was responsible for the formation of these deposits. To explore the implications of such a boron enriched environment on microbial activity, modes of occurrence and chemical compositions of the tourmaline were examined. <br/> The tourmaline is schorl or dravite of the alkali tourmaline group and the boron isotope compositions range in ƒΒ11B from -7.3 to +2.6ρ. The tourmaline occurs in microcrystalline quartz matrix of black chert veins that cross cut a volcanic unit and also in a bedded black chert, which overlays the volcanic unit. The volcanic unit contains highly altered zones with hydrothermal veins. The associated lithologic and stratigraphic features suggest that the black chert veins were the conduits for upward moving hydrothermal fluids, which reached the sea floor. Subsequently, the volcanic unit was covered by organic matter-rich cherty sediments that in part were fed, and/or altered, by the hydrothermal fluids. <br/> These results suggest that the origin of boron enrichment to form Dixon Island tourmaline is not the associated sedimentary mineral assemblage, which includes diagenetic clay, low-grade metamorphic mica, and organic matter. Instead, the tourmaline was directly precipitated from hydrothermal fluid, enriched in boron. Furthermore, the hydrothermal fluids had already concentrated the boron, in the Mesoarchean pelagic system, prior to the apex of organic matter production and microbial activity. Our findings support a hypothesis that the boron-enriched hydrothermal environment aided the survival and evolution of early life. No potential conflict of interest relevant to this article was reported.

John Wiley Acta Medica Okayama 16394488 43 4 2019 Method to Suppress Isobaric and Polyatomic Interferences for Measurements of Highly Siderophile Elements in Desilicified Geological Samples 611 633 EN Xiaoyu Zhou The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Masahiro Yamanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Chie Sakaguchi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Carius tube or high]pressure asher) is the most common method used to extract highly siderophile elements (HSEs: Ru, Rh, Pd, Re, Os, Ir, Pt and Au) from geological samples. Recently, it has been recognised that additional HF desilicification is necessary to better recover HSEs, potentially contained within silicate or oxide minerals in mafic samples, which cannot be dissolved solely by inverse aqua regia. However, the abundance of interfering elements tends to increase in the eluent when conventional ion]exchange purification procedures are applied to desilicified samples. In this study, we developed an improved purification method to determine HSEs in desilicified samples. This method enables the reduction of the ratios of isobaric and polyatomic interferences, relative to the measured intensities of HSE isotope masses, to less than a few hundred parts per million. Furthermore, the total procedural blanks are either comparable to or lower than conventional methods. Thus, this method allows accurate and precise HSE measurements in mafic and ultramafic geological samples, without the need for interference corrections. Moreover, the problem of increased interfering elements, such as Zr for Pd and Cr for Ru, is circumvented for the desilicified samples. No potential conflict of interest relevant to this article was reported.

Springer Nature Publishing AG Acta Medica Okayama 20411723 10 1 2019 Origin of ocean island basalts in the West African passive margin without mantle plume involvement 3022 EN Iyasu Getachew Belay The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Ryoji Tanaka The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Hiroshi Kitagawa The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Katsura Kobayashi The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University Eizo Nakamura The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University The geochemical variabilities in intraplate basalts (IB) from the West African passive margin (WAPM) region, have generally been employed to indicate the presence of recycled materials in an associated upwelling mantle plume. However, the absence of time-progressive linear hotspot tracks in WAPM-IB make it difficult to explain their genesis solely by the mantle plume hypothesis. Here, we show that the Sr–Nd–Hf–Pb isotopic variations in basalts from most of the WAPM-IB could have mainly attributed to the derivation from two types of fusible regions of the refertilized subcontinental lithospheric mantle (SCLM) and the sub-lithospheric mantle. The locations and magma genesis of WAPM-IB are strongly related to the distance from the Mesozoic rift axis and the structure of the rifted SCLM. The melting of the source region can possibly be attributed to small-scale mantle convection at the base of the SCLM without the involvement of a mantle plume. No potential conflict of interest relevant to this article was reported.