Abstracts of Annual Meeting of the Geochemical Society of Japan

Thermo disintegration, nuclear reaction with nutrino, and capture reaction of proton, etc. are considered for a nucleo synthesis of proton-rich nuclei, p-nuclei, which exist in the present solar system. However, the detailed processes have not been understood. In this work, we computed abundance of the p-nuclei around mass number 140 based on the proton capture reaction to construct evolution of the isotopic abundance. Information about temperature, time, and density for explaining the present abundance of the p-nuclei, were obtained from the simulation.

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We analyzed halogens and noble gases in H?SUB?2?/SUB?O-rich fluid inclusions in mantle peridotites from subduction zones (Kamchatka, N. Phillipines, and N. Japan). Their compositions are similar to those of marine sedimentary pore water, putting a constraint on the subduction process of such water into the mantle.

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In our study, the improved J?rgensen equation for the tetrad effect of REE?/SUP?3+?/SUP? were employed to fit the chondrite-normalized REE patterns of five kimuraite samples and one lanthanite sample from southwest Japan as well as six kimuraite samples and one lanthanite sample from the Pavlovskoe REE-coal deposit in Russia, since all of them were suggested to display tetrad effects (Akagi et al., 1993; Akagi et al., 1996; Kawabe et al., 2012). In addition, the REE partitioning between kimuraite and lanthanite, which are coexisting REE?SUP?3+?/SUP? species in a hydrothermal fluid, was also examined by the theoretical equation. When the chondrite-normalized REE patterns of two lanthanite samples reported by Nagashima et al. (1986) and Seredin et al. (2009) were applied to the theoretical equation, the former was proved to show a tetrad effect as it can be quantitatively described by the equation, except for the negative Ce anomaly. In contrary, the latter was not able to be reproduced by the equation, as this lanthanite sample is described as an ore sample, which raises the possibility that it is probably not a pure lanthanite. When suitable corrections were made for HREE, it became compatible with the theoretical equation. At the same time, the chondrite-normalized REE patterns of three kimuraite samples from Japan and six kimuraite samples from Russia were investigated by the improved J?rgensen equation. The kimuraite sample of Nagashima et al. (1986) and kimuraite B of Akagi et al. (1993) had their chondrite-normalized REE patterns regressed by the equation, and both of them display W-type tetrad effects. In comparison, the chondrite-normalized REE patterns of the kimuraite of Jiao et al. (2013), as well as all kimuraite samples from Russia, were not able to be reproduced by the equation immediately, if the excessive amount of LREE possibly caused by the contamination of lanthanite was not corrected. This result means the kimuraite samples reported by Seredin et al. (2009) are not pure kimuraite either. Four other samples, which were described as mixtures of kimuraite and lanthanite by Seredin et al. (2009), were immediately fitted by the improved J?rgensen equation with rather faint tetrad effects, suggesting that these samples might represent the REE compositions of a certain homogeneous phase. In addition, the REE partitioning between kimuraite and lanthanite was also studied with the theoretical equation. As a result, the improved J?rgensen equation immediately reproduced the lanthanite-normalized REE patterns of three kimuraite samples, confirming that the fractionation pattern of REE between kimuraite and lanthanite can yield a faint tetrad effect. The convex octad effect for lanthanite-normalized REE pattern is consistent with the larger coordination number of REE?/SUP?3+?/SUP? in lanthanite relative to that in kimuraite, though the intrinsic tetrad effects are concave.

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