Abstracts of Annual Meeting of the Geochemical Society of Japan

Geochemical studies on melt inclusions proposed that H2O-rich crustal magmas often suffer CO2 fluxing. In order to explore kinetics of H2O-CO2 interaction upon CO2 fluxing, we conducted volatile exchange experiments in an H2O-CO2-rhyolite system. We observed that bubbles pre-existing in an H2O-rich magma may dissolve to shrink as a result of volatile exchange with a CO2-rich fluxing fluid.

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Sulfur is the sixth most abundant element in the whole Earth and may be one of the light elements in the Earth's core. It carries the potential as a key to constrain chemical distribution in view of mantle-core interaction.Some pioneering works tried to analyze sulfur isotopic ratio of oceanic basalt. It shows a uniform value that is within the range of iron meteorites. In addition, local variation in sulfur isotope ratio outside the normal mantle value used to be ascribed to solubility controlled degassing fractionation.
We will present newly detected sulfur isotope ratios of Loihi lavas whose variation cannot be interpreted only by the equilibrium degassing fractionation or contamination with seawater.

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^87/86Sr and ^143/144Nd for late-Pliocene to Quaternary volcanic rock in Aso area in SW Japan, were determined to reveal temporal changes of the magma characteristics and a mechanism of magmatic system. Isotopic ratios of volcanic products at each period distributed in Sr-Nd isotopic diagram are as follows. 1) early pre-caldera period: separately distributed in two areas (component A: around (0.7040, 0.51285), component B: around (0.7044, 0.51270), 2) late pre-caldera period: distributed between component A and B along mantle array, 3) intercaldera period: distributed within the area of caldera forming period (excepting for ratios of Neko-dake), 4) post-caldera period: distributed between component A and B like that of late pre-caldera period. Source materials of volcanic products of each period are inferred from these results. Two components (A and B) of volcanic rocks in early pre-caldera period are related to source materials of volcanic products both in late pre-caldera and post-caldera period , or crustal material made this variation in these periods as contaminating to component A. Geochemical characteristics of post-caldera volcanic products are not same as that of inter-caldera and caldera period, and this implicates that magma process of post-caldera was changed.

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Limited number of research reports describing to behavior of deep groundwater with measured age is available. So, it is needed for the planning to deep repository of radioactive waste to investigate of behavior and cumulate database of residence time of deep groundwater flow system. In this paper, several geochemical dating methods such as H-3 dating method, C-14 dating method and Cl-36 dating method were applied to the groundwater sampled from several hundred meters of borehole and these geochemical residence time were estimated. The sampling of the groundwater from the surface level to the 350 m deep level below the ground surface was used by multi-packer system by step by step of the depth.
As a result, an clear difference of the trace concentration of each radioactive natural nuclides is obtained. So it indicate that the groundwater system at the site has multi layered groundwater flow.

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