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The four stable halogens (F, Cl, Br, and I) are low-abundance elements that are widely distributed in nature. Two of the halogens, Cl and Br, each have two stable isotopes showing a range in natural isotope variation of up to a few parts per thousand. A variety of analytical techniques have been developed to determine the abundance and isotopic ratios of the halogens: these include in situ techniques for high spatial resolution studies and bulk determinations, and they have been applied to a range of materials, including whole rocks, minerals, glasses, and fluid inclusions. Here, we summarise some of the established methods for determining halogen abundances and isotopes and highlight key advances.

Considering the expanding demand for nuclear waste management of the spent nuclear fuel materials in near future, a nondestructive analytical scheme applicable to one of the most difficult-to-measure nuclides 107Pd, which emits no decay γ-rays and whose half-life is too long to be decayed out during a human lifetime, was designed. The scheme consists of a sophisticated instrument capable of the detection of γ-rays by Ge detectors coupled with time-of-flight measurement of neutrons and a high-intensity pulsed neutron beam and can simultaneously perform time-of-flight-coupled prompt γ-ray analysis (TOF-PGA) as well as PGA and neutron resonance capture analysis (NRCA). The analytical capability for simulated samples of the Tc-platinum group metals (Tc-PGMs) obtained by the group-partitioning process of spent nuclear fuels, which contain not only 107Pd but also 99Tc and other difficult-to-measure fission products, was evaluated. It was confirmed that although PGA and NRCA can accurately analyze both nuclides in individual, single substances, only TOF-PGA can analyze 107Pd as well as 99Tc in the Tc-PGM-simulated sample. The TOF-PGA measurement technique can be widely used for the nondestructive analysis of 107Pd and 99Tc in nuclear wastes.

Data of the atmospheric activity concentrations (in Bq/m

Prompt gamma-ray activation analysis (PGAA) was applied to well homogenized meteorite samples initially prepared for the wet chemical analysis. By comparing the PGAA data with wet chemical analysis data in literatures, it was confirmed that PGAA can be alternative or even advantageous to wet chemical analysis in terms of the data reliability. Because the same sample can be analyzed by INAA followed by PGAA, data obtained by a combination of PGAA and INAA were proved to enable us to discuss the detailed chemical characteristics of meteorite samples represented by eucritic meteorites (eucrites).

An igneous clast from the Northwest Africa 773 (NWA 773) clan of lunar meteorites formed by silicic volcanism on the Moon. The clast was identified in Northwest Africa 2727 (NWA 2727), which is included in the NWA 773 clan. Over 80 mode% of the clast consists of silica + plagioclase + K-Ba-feldspar. The silica phases cristobalite, tridymite, and quartz are all present in the clast, indicating rapid cooling at low pressure in agreement with a volcanic setting. This clast is characterized as a dacite on the basis of mineral modes and whole-rock chemical composition. Olivine and pyroxene in the clast have high Fe/Mg ratios (olivine Fe# > 99, pyroxene Fe# > 99; with Fe# = molar Fe/(Fe + Mg) × 100), suggesting crystallization from a residual liquid after fractionation of more magnesian silicates. The clast is similar in some respects to ferroan gabbro alkaline-phase-ferroan (FG/ARFe) clasts that are inferred to be co-magmatic with olivine gabbro (OG) and other mafic lithologies of the NWA 773 clan. However, the high silica concentration and dominance of apatite as the main Ca-phosphate (no merrillite was identified) are distinct from the FG/ARFe clasts. Thus, the dacite clast probably crystallized in a magmatic setting that was independent of the OG and FG/ARFe lithologies. The mafic major element composition, young age, and high KREEP-content of the NWA 773 clan have been used previously to infer an origin from the Procellarum-KREEP terrane (PKT) on the nearside of the Moon. Several candidates for silicic volcanism/plutonism have been identified in the PKT (e.g., Gruithuisen Domes, Hansteen alpha, Lassell Massif). The presence of the dacite lithology provides additional support for an origin in or around PKT for meteorites of the NWA 773 clan, and for complex igneous activity in PKT region.

We have determined the hourly atmospheric concentrations of

Considering the expanding demand for nuclear waste management of the spent nuclear fuel materials in near future, a nondestructive analytical scheme applicable to one of the most difficult-to-measure nuclides

Instrumental neutron activation analysis (INAA), inductively coupled plasma atomic emission spectrometry (ICP-AES) and ICP mass spectrometry (ICP-MS) (hereafter, ICPs) were applied to meteorite samples for the determination of elemental content. The analytical applicability and suitability of the three methods have been compared. Those comparisons led to the refinement of our analytical procedures for INAA and ICPs, yielding more reliable data. Our INAA data proved to be reliable enough for classifying meteorites, while the ICPs, especially ICP-MS, can characterize elemental abundance features in detail, as demonstrated by REE abundance patterns for the Allende meteorite. In this manner, INAA and ICPs can be used in a complementary fashion in cosmochemical studies.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2018-01-25, 資料番号: PA1810047000

Lunar meteorites provide information about areas of the Moon not sampled by the Apollo and Luna missions, so they can be used as more-representative geochemical datasets for evaluating global lunar evolution. However, the launching craters remain unknown for many lunar meteorites. This paper, therefore, aims to identify the launching sites of lunar meteorites with remote-sensing datasets. This work focuses on one lunar-meteorite group, the Northwest Africa 773 (NWA 773) clan, which has the very-low-Ti basaltic composition and one of the youngest crystallization ages (~3 Ga) among the lunar basaltic meteorites. We investigated the source of the NWA 773 clan by comparing their geochemical compositions and geochronological information with the following remote-sensing datasets: 1) the Lunar Prospector gamma-ray elemental maps (FeO, TiO2, Th) and the SELENE gamma-ray elemental maps (CaO), 2) the surface ages determined from imaging data by using the crater-counting method, and 3) high-spatial-resolution maps of the FeO and TiO2 and spectral-ratio images made from the SELENE multi-band imager data. From these comparisons, the NWA 773 clan is most likely to have originated from the north part of Mare Imbrium inside the Procellarum KREEP Terrane (PKT). Furthermore, the eruption age of surface basalt surrounding the Le Verrier D crater in the north part of Mare Imbrium between 3.0 and 3.3 Ga, and the formation of the Le Verrier D crater, are consistent with the duration of igneous activity and timing of meteoroid impact of the NWA 773 clan. There is a fresh crater with bright ejecta on the edge of the Le Verrier D crater, and it is possibly the young launch crater of this meteorite group.

The Tsenkher structure in the Gobi-Altai, Mongolia is a c. 3.7 km diameter crater with a well-preserved ejecta blanket. It has been hypothesized to be either of impact or volcanic origin in our previous work. Observations during our 2007 expedition and related sample analyses give further support for an impact origin. The evidence includes the presence of a structurally uplifted near-circular rim surrounded by an ejecta blanket, and abundant breccias, some of which are melt- and millimetre-scale spherule-bearing. Planar deformation features (PDFs) were found in one quartz grain in a breccia sample. Fe-rich grains are found in a vesicular melt sample that is also characterized by elevated platinum group element (PGE) abundances with respect to the sedimentary bedrock of the area (approximately an order of magnitude). Noble gas analysis of one breccia sample yielded an elevated 3He/4He value of (5.0±0.2) × 10−6. Although not conclusive alone, these geochemical results are consistent with a contribution of meteoritic components. A volcanic origin, in particular a maar formation, would require explanations for the unusual conditions associated with Tsenkher, including its large size occurring in isolation, the structurally uplifted rim and the lack of a bedded base surge deposit. A pronounced rampart structure observed at the eastern ejecta is also unusual for any volcanic origin. 40Ar–39Ar dating of a vesicular melt sample gives an age of the Tsenkher structure of 4.9±0.9 Ma. The rampart structure could provide insights into the formation of similar ejecta morphologies associated with numerous impact craters on Mars.

Light insufficiency is a major abiotic stress limiting plant growth and crop yield in intensive greenhouse production. The application of supplemental lighting to the lower canopy is an efficient method to increase irradiation levels in greenhouse tomato cultivation systems. We evaluated the effects of supplemental lighting provided from underneath the canopy (USL) or within the inner canopy (ISL) on leaf photosynthetic traits, plant growth, and fruit development in single-truss tomato plants. Both USL and ISL significantly promoted leaf photosynthetic activities, plant growth, and fruit production in plants exposed to low solar irradiation levels. The use of USL maintained relatively stable light irradiation conditions in the lower canopy. It also promoted photosynthesis through improved CO2 assimilation and stomatal conductance, and contributed more to fruit yield than ISL. However, ISL induced greater increase in fruit soluble solid contents because of higher exposure to direct supplemental light to fruit. Based on physiological outputs and an energy cost performance analysis, the application of USL may be more financially viable than the use of ISL.

We report herewith the study of fingernail clippings obtained from the residents of Tokyo, Japan. A total of 18 participants with no health problems and occupational exposure to metals were recruited to provide fingernails samples for this study. Through the use of instrumental neutron activation analysis (INAA), 18 elements (Ag, Al, As, Ca, Cl, Co, Cu, Fe, Hg, K, Mg, Mn, Na, S, Sb, Se, V, and Zn) were determined. The results showed that the toxic elements in the fingernails are in the lower range when compared to literature values. There were no chronic exposures to toxic elements such as As and Hg found. The level of Hg found is lower than that reported 20 years ago, possibly due to the strict regulation control in Japan on the release of Hg to the environment. The elements Se and Zn are found to be rather uniformly distributed among participants and are in agreement with results from other countries. There were no significant differences in elemental concentrations due to genders and smoking habits. The overall data from this study showed similar concentrations to those of healthy participants from other countries. Thus, the current data could represent the background level of elemental concentrations in fingernails of residents in Tokyo, which could serve as reference values for future study.

The unique occurrence of abundant (~1 vol%) near-pure-Fe metal in the Camel Donga eucrite is more complicated than previously believed. In addition to that component of groundmass metal, scattered within the meteorite are discrete nodules of much higher kamacite abundance. We have studied the petrology and composition of two of these nodules in the form of samples we call CD2 and CD3. The nodules are ovoids 11 (CD2) to 15 (CD3) mm across, with metal, or inferred preweathering metal, abundances of 12–17 vol% (CD2 is unfortunately quite weathered). The CD3 nodule also includes at its center a 5 mm ovoid clumping (6 vol%) of F-apatite. Both nodules are fine-grained, so the high Fe metal and apatite contents are clearly not flukes of inadequate sampling. The metals within the nodules are distinctly Ni-rich (0.3–0.6 wt%) compared to the pure-Fe (Ni generally 0.01 wt%) groundmass metals. Bulk analyses of three pieces of the CD2 nodule show that trace siderophile elements Ir, Os, and Co are commensurately enriched; Au is enriched to a lesser degree. The siderophile evidence shows the nodules did not form by in situ reduction of pyroxene FeO. Moreover, the nodules do not show features such as silica-phase enrichment or pyroxene with reduced FeO (as constrained by FeO/MgO and especially FeO/MnO) predicted by the in situ reduction model. The oxide minerals, even in groundmass samples well away from the nodules, also show little evidence of reduction. Although the nodule boundaries are generally sharp, groundmass-metal Ni content is anti-correlated with distance from the CD3 nodule. We infer that the nodules represent materials that originated within impactors into the Camel Donga portion of the eucrite crust, but probably were profoundly altered during later metamorphism/metasomatism. Origin of the pure-Fe groundmass metal remains enigmatic. In situ reduction probably played an important role, and association in the same meteorite of the Fe-nodules is probably significant. But the fluid during alteration was probably not (as previously modeled) purely S and O, of simple heat-driven internal derivation. We conjecture a two-stage metasomatism, as fluids passed through Camel Donga after impact heating of volatile-rich chondritic masses (survivors of gentle accretionary impacts) within the nearby crust. First, reduction to form troilite may have been triggered by fluids rich in S2 and CO (derived from the protonodules?), and then in a distinct later stage, fluids were (comparatively) H2O-rich, and thus reacted with troilite to form pure-Fe metal along with H2S and SO2. The early eucrite crust was in places a dynamic fluid-bearing environment that hosted complex chemical processes, including some that engendered significant diversity among metal+sulfide alterations.

We report petrology and geochemistry of an achondrite EET 92023 and compare it with normal and anomalous eucrites. EET 92023 is an unbrecciated achondrite and shows a granular texture mainly composed of low-Ca pyroxene and plagioclase, petrologically similar to normal cumulate eucrites such as Moore County. However, this rock contains a significant amount of kamacite and taenite not common in unbrecciated, crystalline eucrites. EET 92023 contains a significant amount of platinum group elements (PGEs) (ca. 10% of CI), several orders of magnitude higher than those of monomict eucrites. We suggest that the metallic phases carrying PGEs were incorporated by a projectile during or before igneous crystallization and thermal metamorphism. The projectile was likely to be an iron meteorite rather than chondritic materials, as indicated by the lack of olivine and the presence of free silica. Therefore, the oxygen isotopic signature is indigenous, rather than due to contamination of the projectile material with different oxygen isotopic compositions. A significant thermal event involving partial melting and metamorphism after the impact event indicates that EET 92023 records early impact events which took place shortly after the crust formation on a differentiated protoplanet when the crust was still hot.

INAA, ICP-AES and ICP-MS were used to elementally characterise four environmental reference materials – NIST SRM 1646a (Estuarine Sediment), NIST SRM 1400 (Bone Ash), IAEA-395 (Urban Dust) and IAEA-450 (Algae). An analytical scheme consisting of the three methods was first applied to NIST SRM 1646a to validate the methodology because it has been extensively analysed and has certified values for many elements. With repeated analyses of NIST SRM 1646a, the accuracy and measurement repeatability of the data obtained were evaluated based on two statistical calculations (zeta-score and Horwitz ratio) and were observed to be good enough for the analytical scheme to be applied to similar sorts of environmental/geochemical samples. Applying the same approach to NIST SRM 1400, IAEA-395 and IAEA-450, enabled mass fractions of 29, 38 and 28 elements to be determined, respectively. Among these results, the data for rare earth elements are of particular interest, not only for IAEA-450 but also for the other three reference samples. The data for Pr, Gd, Dy, Ho, Er and Tm in NIST SRM 1646a are newly reported in this study. By using small test portions (

The Fukushima Dai-ichi Nuclear Power Plant accidents following the March 11, 2011 Tohoku earthquake, and subsequent tsunami released radioactive materials into the atmosphere and caused significant public health concerns, particularly thyroid cancers in children. However, the lack of measurement data for atmospheric concentrations of

To retrieve the diffusion trajectory of the

The amount of 137Cs released by the Fukushima Dai-ichi Nuclear Power Plant accident of 11 March 2011 was inversely estimated by integrating an atmospheric dispersion model, an a priori source term, and map of deposition recorded by aircraft. An a posteriori source term refined finer (hourly) variations comparing with the a priori term, and estimated 137Cs released 11 March to 2 April to be 8.12 PBq. Although time series of the a posteriori source term was generally similar to those of the a priori source term, notable modifications were found in the periods when the a posteriori source term was well-constrained by the observations. Spatial pattern of 137Cs deposition with the a posteriori source term showed better agreement with the 137Cs deposition monitored by aircraft. The a posteriori source term increased 137Cs deposition in the Naka-dori region (the central part of Fukushima Prefecture) by 32.9%, and considerably improved the underestimated a priori 137Cs deposition. Observed values of deposition measured at 16 stations and surface atmospheric concentrations collected on a filter tape of suspended particulate matter were used for validation of the a posteriori results. A great improvement was found in surface atmospheric concentration on 15 March; the a posteriori source term reduced root mean square error, normalized mean error, and normalized mean bias by 13.4, 22.3, and 92.0% for the hourly values, respectively. However, limited improvements were observed in some periods and areas due to the difficulty in simulating accurate wind fields and the lack of the observational constraints.

Trace amounts of three halogens (chlorine, bromine and iodine) in seventeen U.S. Geological Survey (USGS) geochemical reference materials were determined by radiochemical neutron activation analysis (RNAA). The materials analysed were AGV-2 (andesite), BCR-2, BHVO-2 and BIR-1a (basalts), CLB-1 (coal), COQ-1 (carbonatite), DGPM-1 (disseminated gold ore), DNC-1a (dolerite), DTS-2b (dunite), GSP-2 (granodiorite), Nod-A-1 and Nod-P-1 (manganese nodules), QLO-1a (quartz latite), SBC-1 (marine shale), SDC-1 (mica schist), SGR-1b (shale rock) and W-2a (diabase). The chlorine, bromine and iodine contents were determined to be 5.64 mg kg−1 (BIR-1a) to 4410 mg kg−1 (Nod-A-1), 0.039 mg kg−1 (BIR-1a) to 52.1 mg kg−1 (CLB-1), and 0.041 mg kg−1 (BIR-1a) to 599 mg kg−1 (CLB-1), respectively. The RNAA data of the three halogens were compared with the corresponding data in the literature.

An instrumental neutron activation analysis (INAA) procedure for analyzing extremely small samples was developed and applied to two kinds of extraterrestrial samples. A few mg of the Allende meteorite as well as the JB-1 basalt can work well as a reference sample for a relative method. To evaluate the applicability of this INAA procedure, detection limits are presented and compared with the elemental contents in a potential sample to be analyzed. The possibility of reuse of neutron-irradiated samples for mass spectrometry was noted by indicating degree of increase in isotopic abundance for noble gas and long-lived radioactive nuclides.

Petrological, mineralogical and geochemical studies were performed on five brecciated HED meteorites (ALH 76005, EET 92003, LEW 85300, LEW 87026 and GRO 95633) in order to elucidate the nature of impactors on the HED parent body. Some brecciated HED meteorites contain exotic materials such as FeNi-metal grains with low Co/Ni ratios (ALH 76005, EET 92003 and GRO 95633) and carbonaceous chondrite clasts (LEW 85300) in a clastic and/or impact melt matrix. Such exotic materials were incorporated during brecciation. Platinum group element (PGE) abundances vary significantly (CI × 0.002–0.05), but are higher than those of pristine rocks from the HED parent body. The PGE ratios for the five HED meteorites are inconsistent with each other, implying that the impactor components of each HED meteorites are different from each other. The various PGE ratios are consistent with those for metals from chondrites and iron meteorites, and carbonaceous chondrites. This study provides the evidence that IAB and IVA iron meteorites, and carbonaceous chondrites (CM, CO, CV, CK, CB and CR), ordinary chondrites (L and H) and enstatite chondrite (EL) are candidates of the impactor materials on the HED parent body. It is highly probable that significant amounts of siderophile elements were incorporated into the inner solar system objects like the HED parent body from both chondritic materials and differentiated materials like iron meteorites during heavy bombardment. The HED meteorites in this study and metals from mesosiderite have different Pd/Ir ratios, probably implying that HED meteorites and mesosiderites formed either at distinct settings on one common parent body or on similar parent bodies.

Positive platinum group element (PGE) concentration and negative Os isotope anomalies reported from a claystone layer in the Upper Triassic bedded chert succession of the Sakahogi section, Mino Belt, central Japan, are thought to have been derived from an impact event. Stratigraphic variations and concentrations of PGE were examined in the Sakahogi section to determine the type of the impactor. Upper Triassic claystone layers, where PGE anomalies have been newly discovered in bedded chert successions in southwest Japan, were also examined. These include (i) the Unuma section in the Inuyama area, Mino Belt; (ii) the Hisuikyo section in the Kamiaso area, Mino Belt; and (iii) the Enoura section in the Tsukumi area, Chichibu Belt. Radiolarian and conodont biostratigraphic data indicate that these claystone layers are of upper–middle Norian age. Reconstruction of bedded chert in these sections suggests that they originate from open-ocean pelagic deep-sea sediments deposited in the Panthalassa Ocean. The relatively flat CI chondrite-normalized patterns of the least mobile PGEs (Ir, Ru, and Rh) and the Ru/Ir ratio determined by linear regression analysis suggest that a chondritic impactor is the source of the PGE anomalies preserved in claystone samples from the study sections. Although Ru/Ir ratios cannot conclusively distinguish chondrites from iron meteorites, the Cr/Ir ratios of the claystone layers range from 10 4 to 10 5 , clearly indicating contribution from chondritic materials. The chondritic impactor of the suggested size (3.3–7.8 km in diameter) implies that a large amount of debris and/or climatically active gasses (e.g., sulfur oxides) would have been released from the impactor, which would have had a marked effect on the environment.

The Fukushima Dai-ichi Nuclear Power Plant accidents following the March 11, 2011 Tohoku earthquake, and subsequent tsunami released radioactive materials into the atmosphere and caused significant public health concerns, particularly thyroid cancers in children. However, the lack of measurement data for atmospheric concentrations of 131I has caused persistent and widespread uncertainty. This study estimated the maximum potential thyroid doses of inhaled 131I in the early post-accident phase between March 12 and 23, 2011 by using the hourly measured data of the 137Cs concentrations at 101 suspended particulate matter (SPM) monitoring sites, a new multi-model ensemble (MME) method of simulating 137Cs concentrations using two Atmospheric Transport and Deposition Models (ATDMs), the 131I/137Cs ratio obtained from measurement data analysis, and the internal exposure model. Based on the measurements, the maximum potential thyroid doses were estimated at 3.1–160 mSv at 5 sites in the Fukushima-Hamadori area for 1-year-old children assumed to remain outdoors, whereas they were less than 4.3 mSv at the other sites in the base case of the 131I/137Cs ratio. The spatial distribution of the maximum potential of early inhalation doses was estimated by using the MME and measurements. The inhalation thyroid doses in the evacuation scenarios were compared to the estimates reported by previous studies. The results of the present study were almost congruent with the outcomes of previous investigations except for thyroid doses contributed by highly contaminated plumes on March 12 and 15. The sensitivity analysis for the 131I/137Cs ratio indicated that these plumes carried the potential to significantly increase the thyroid doses of residents.

International audience; Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011, atmospheric simulation models have improved our understanding of the atmospheric behavior of radionuclides. Model intercomparisons provide valuable and useful information for evaluating the validity and variability of individual model results. In this study, we compared results of seven atmospheric transport models used to simulate 137Cs released from the FDNPP to the atmosphere. All model results used in this analysis had been submitted for a model intercomparison project of the Science Council of Japan (2014, http//www.scj.go.jp/en/report/index.html). Here we assessed model performance by comparing model results with observed hourly atmospheric concentrations of 137Cs, with a particular focus on nine plumes over the Tohoku and Kanto regions. The intercomparison results showed that model performance in reproducing 137Cs concentrations was highly variable among different models and plumes. In general, models better reproduced plumes that passed over many observation stations. The performance among the models was consistent with the simulated wind fields and the source terms used. We also assessed model performance in relation to accumulated 137Cs deposition. Simulated areas of high 137Cs deposition were consistent with the simulated 137Cs plume pathways, though the models that best simulated atmospheric 137Cs concentrations were different from those that best simulated deposition. The ensemble mean of all models consistently reproduced atmospheric 137Cs concentrations and deposition well, suggesting that use of a multimodel ensemble results in more effective and consistent model performance. ©2018. American Geophysical Union. All Rights Reserved.

57Fe Mossbauer spectroscopy was applied to compositional studies of Fe-containing minerals in two different ordinary chondrites, MIL 07710 (L4) and Y-790272 (H4), collected in Antarctica. For both samples, spectral analysis revealed that there are five quadrupole doublets and two magnetic sextets in the room-temperature spectra, suggesting the presence of olivine (M1 and M2), pyroxene (M1 and M2), a high-spin Fe3+ containing phase, antiferromagnetic FeS (troilite), and ferromagnetic Fe-Ni alloy. The large relative area of the oxidized Fe3+ phases and the small intensity of the metal phases signify a possible effect of terrestrial weathering especially for Y-790272 (H4).

Rare earth elements (REEs), Th, U and P were determined in 15 Rumuruti (R)-type chondrites and the Allende CV chondrite. Repeated analyses of Allende for REEs, Th and U by ICP-MS and P by ICP-AES, and comparisons of these data with literature values ensure high reproducibility (precision) and reliability (accuracy) of acquired data. CI-normalized REE abundances in R chondrites are slightly enriched in heavy REEs with a small, positive Ce anomaly, in contrast to Allende. CI-normalized Pr/Tm and Nd/Yb ratios show a positive correlation, suggesting the heterogeneous mixing of two components (CI-like and refractory-rich materials) during the accretion of the R chondrite parent body. A Ce anomaly, however, was likely homogeneously present in the nebula. A mean Th/U ratio of R chondrites is 3.81 ± 0.13 ( 1 σ ) , which is 5.1% higher than the CI ratio. Probably, the Th–U fractionation was inherited from the nebula from which the R chondrite parent body formed. Besides the Th–U fractionation, REEs and Th–U are heterogeneously fractionated in R chondrites, for which parent body processing is assumed to be the cause. A mean P content of R chondrites (1254 μg/g) is higher than for any ordinary chondrite and is close to the EL mean. There appears to be a negative correlation between P and REEs contents in R chondrites. It is probable that REEs were diluted by extraneously supplied, REEs-depleted and P-containing materials (schreibersite or metal). This process must have occurred heterogeneously during accretion so that the heterogeneity of P-containing materials was preserved in the R chondrite parent body and individual R chondrites.

著者人数: 16名, 資料番号: SA1150052000

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 ∼5 µm-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 (∼15 × 15 μm) in its interior. Low-Ca pyroxene is much more abundant than olivine and shows various Mg/(Mg + Fe) ratios ranging from ∼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 ∼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, 13C, or 15N 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., アクセプト後にタイトル・アブストラクト等変更あり、著者最終稿は変更前のタイトル"Formation of an Ultracarbonaceous Antarctic Micrometeorite through Minimum Aqueous Alteration in a Small Porous Icy Body", This work was supported by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Culture, Sports, Science and Technology (No. 22224010, PI: H. Nagahara). The STXM facility at the beamline 5.3.2.2, ALS, is supported by the Department of Energy, Basic Energy Sciences Program.