New stellar sources for high-density, presolar graphite grains

WepresentC,N,O,Si,Al-Mg,K,Ca,andTiisotopicanalyses ofsevenhigh-density(ORG1f, � � 2:02 2:04 gcm � 3 ) graphite grains from Orgueil with 12 C/ 13 C ratios smaller than 20. The presence of 44Ti in three of these grains indicates an origin in Type II supernovae (SNe). The 13 C excesses in these SNe grains, however, remain enigmatic. The remaining grains have extremely large Ca and Ti isotopic anomalies, some of which are much larger than those predicted for envelopes of asymptotic giant branch (AGB) stars. These anomalies in conjunction with low 12 C/ 13 C ratios can only be explained by pure nucleosynthetic He-shell components of AGB stars. Born-again AGB stars that experience a late He flash are able to explain the low 12 C/ 13 C ratios of some of the grains along with the presence of extreme enrichments in the Ca and Ti isotopes. This study indicates that high-density graphite grains havemultiple stellar sources: SNe and born-again AGB stars, in addition to the previously established low-metallicity AGB stars. Subject headingg dust, extinction — meteors, meteoroids — nuclear reactions, nucleosynthesis, abundances — stars: abundances — stars: AGB and post-AGB — supernovae: genera

Reexamination of purely physical separation of the phase enriched in noble gases from the Allende meteorite

We have prepared a new sample of the "floating fraction" of the Allende meteorite and have analyzed the elemental and isotopic compositions of the noble gases to examine the properties of the separation technique. The "floating fraction" is the black fine material, which floats on the water during freeze-thaw disaggregation. The floating fraction separated in this study was enriched in noble gases, and its isotopic compositions were very similar to those of chemical residues. We thus confirmed that the physical separation is an effective method to obtain a noble-gas-rich fraction than the chemical treatment. The only major difference between our floating fraction and those previously prepared was that the former had small excesses in ^Ar and ^Xe which were supposed to be due to the contamination from small amounts of silicate like sodalite. There were some variations in the Xe-Q/Xe-HL ratios among floating fractions, suggesting that Q-and HL-components might be separable by a physical process

A laboratory experiment on the influence of aqueous alteration on noble gas compositions in the Allende meteorite

We have carried out a hydrothermal experiment on the Allende CV chondrite, in order to understand the observed noble gas loss from CM and CI chondrites, possibly caused by aqueous alteration on their parent bodies (L. B. Browning et al., Geochim. Cosmochim. Acta, 60,2621,1996; T. Nakamura et al., Geochim. Cosmochim. Acta, 63,257,1999). The Allende meteorite was disaggregated and kept with liquid water in a pressurized vessel under 15 atm of water vapor at 200℃ for a week. The abundances of helium, neon, argon, krypton and xenon in the samples have been measured by stepwise heating technique. The abundances of noble gases were decreased by 24% (He), 27% (Ne), 38% (Ar), 23% (Kr) and 34% (Xe) after the hydrothermal treatment, suggesting that the hot water treatment had contributed to reduce the concentrations of noble gases in Allende. This gas loss also affected the isotopic composition of xenon. For the 1200℃ fraction, the amount of ^Xe-HL was decreased from the sample by about 80% during the hot water treatment, while that of ^Xe-Q was decreased to a lesser extent (∿40%). This result seems to indicate that the carrier of Xe-HL is less resistant to the gas loss by the hot water alteration than phase Q for high temperature components. However, further studies are required as this trend becomes less obvious and rather similar if we take into consideration the xenon of 800℃ fraction

Neon isotopic composition of carbon residues from the Canyon Diablo iron meteorite

We analyzed noble gases in acid residues extracted from the Canyon Diablo iron meteorite by density and colloidal separation. The results do not indicate any significant variation among the samples although spallogenic noble gases were effectively removed by the treatment. The isotopic compositions of the heavy noble gases are close to those of the terrestrial atmosphere, suggesting that the samples were seriously contaminated by atmospheric noble gases during the treatment. However, the Ne isotopic ratios fall between atmospheric Ne and planetary Ne, suggesting that the primordial component of the noble gases in carbonaceous material in Canyon Diablo is planetary rather than solar

Characterization of sulfate mineral deposits in central Thailand

In this paper we present petrographic and geochemical data of sulfate mineral deposits in northeast Nakhon Sawan, central Thailand, and provide new constraints on their age. The deposits are made up mainly of strongly deformed nodular and massive gypsum in the upper part, and less deformed layered anhydrite in the lower part. They are intruded by andesitic dikes that contain Middle Triassic zircons (ca 240 Ma). These dikes are probably part of the regional magmatic activity of the Sukhothai Arc during the Early to Middle Triassic. Sulfur (δ34S) and strontium (87Sr/86Sr) isotopic compositions of the sulfates range from 15.86‰ to 16.26‰ and from 0.70810 to 0.70817, respectively. Comparisons with the Phanerozoic seawater isotopic evolution curve indicate that those values are best explained by precipitation of the sulfates from Carboniferous seawater, in particular seawater of late Mississippian age (ca 326 Ma), and this would be consistent with previous studies of calcareous fossils in the limestones that crop out around this site. Our interpretation is that evaporitic gypsum was originally precipitated from hypersaline seawater on a shallow lagoon or shelf on the Khao Khwang Platform during the Serpukhovian, and that this gypsum changed to anhydrite during early burial. The anhydrite was then cut by andesitic dikes during the Middle Triassic, and more recently the upper part of which was rehydrated during exhumation to form secondary gypsum near the surface

Phase equilibrium modeling of pelitic gneiss and the origins of carbon in the graphite from Rundvagshetta in the Lützow-Holm Complex, East Antarctica

第6回極域科学シンポジウム[OG] 地圏11月16日（月）　国立極地研究所１階交流アトリウ

Tritium and iodine-129 concentrations in precipitation at Tsukuba, Japan, after the Fukushima Daiichi Nuclear Power Plant accident

The earthquake off the Pacific coast of Japan and the subsequent tsunami on March 11, 2011, triggered a series of accidents in the Fukushima Daiichi Nuclear Power Plant (FNPP1). The accidents caused the release of a mixture of radioactive substances into the environment. This study measured the concentration of tritium (3H) and iodine-129 (129I) in rainwater samples collected at Tsukuba, 170 km southwest of the plant, during the year following the accident. High 3H concentrations were observed in the rainwater samples collected within one month after the FNPP1 accident. 3H concentrations decreased steadily over time and returned to the levels before the accident. Concentrations of 129I also decreased over time. However, pulses of high 129I concentrations were observed at several other times following the accident. The 129I concentrations were found to be correlated with iron concentrations in rainwater. It is likely that iron oxide, which can absorb iodate ions (IO3–), was the carrier of radiogenic iodine. This study concludes that 129I and also 131I, which is one of the most harmful radionuclides produced in nuclear reactors, can be redistributed to the atmosphere in the months following the deposition of radiogenic iodine on the ground

Sulphur geodynamic cycle

Evaluation of volcanic and hydrothermal fluxes to the surface environments is important to elucidate the geochemical cycle of sulphur and the evolution of ocean chemistry. This paper presents S/3He ratios of vesicles in mid-ocean ridge (MOR) basalt glass together with the ratios of high-temperature hydrothermal fluids to calculate the sulphur flux of 100 Gmol/y at MOR. The S/3He ratios of high-temperature volcanic gases show sulphur flux of 720 Gmol/y at arc volcanoes (ARC) with a contribution from the mantle of 2.9%, which is calculated as 21 Gmol/y. The C/S flux ratio of 12 from the mantle at MOR and ARC is comparable to the C/S ratio in the surface inventory, which suggests that these elements in the surface environments originated from the upper mantle.UTokyo Research掲載「硫黄が大気、海洋、マントルを巡る様子」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/deep-sulfur-cycle-involving-atmosphere-ocean-and-mantle.htmlUTokyo Research "Deep sulfur cycle involving atmosphere, ocean and mantle" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/deep-sulfur-cycle-involving-atmosphere-ocean-and-mantle.htm