Formation of Fe(II)-silicate minerals and Mg-silicate minerals at ambient temperature is important in discussions of low-temperature serpentinization or mineral precipitation in the ocean. In this study, minerals were synthesized in Fe(II)-Si-H₂O and Mg-Si-H₂O systems at room temperature and pressure under a nitrogen atmosphere. Fe(II) and Mg silicates formed in the experiments were identified as low-crystalline clay minerals. The experiments clarified solution conditions for formation of the silicate phases.

Europium (Eu), one of rare earth elements (REEs), has been an important element among REE in geochemistry, since Eu can be present both as Eu(II) and Eu(III) under physico-chemical condition of the earth.X-ray absorption near-edge structure (XANES) spectra for trace amount of Eu (＜1 mg/kg) in natural samples were determined in fluorescence mode using Bragg-type crystal analyzer system. Effective separation of Eu Lα and Mn Kα emissions by the system allowed us to measure XANES with high sensitivity. Sharpening of the XANES peak by the suppression of the inner-shell lifetime-broadening effectusing high energy resolution fluorescence detection (HERFD) also contributed to determination of small amount (= 0.01) of Eu(II) relative to Eu(III) based on XANES spectra.

Leading-edge surveys by Mars rovers enable us to apply geochemical techniques like laboratory experiments and modeling to reproduce early Martian environments. While widespread hydrated minerals support an aqueous early Mars, the mechanism achieved clement environment that can possess liquid water on its surface has been debated. One prominent effect that compensated for the greenhouse effect of CO₂ is collision-induced absorption (CIA) caused by mixing molecular hydrogen into the atmosphere. Here, we propose ferrous saponite as a new hydrogen source through the reduction of hydrogen sulfide. Our hydrothermal experiments showed a significant hydrogen generation from the reaction between laboratory synthesized ferrous saponite and hydrogen sulfide. STXM (Scanning Transparent X-ray Microscopy) analysis supports the formation of pyrite particles and oxidation of saponite in mineral phases, supporting that the reduction of sulfur by ferrous saponite caused hydrogen production. As sulfur content in the Martian mantle is high and ferrous saponite is a ubiquitous aqueous alteration product on early Mars, this reaction could have provided hydrogen into the early Martian atmosphere.

Summarizing the results of geological, mineral physics, geophysical and geochemical observations, I will present a model to explain the inferred spatial distribution of water (hydrogen) in the mantle and the long-term stability of the ocean mass. Studies of the sea level show that although fluctuation is large, average sea level has been stable for the last ~600 Myrs. Also based geophysical and geochemical observations suggest that the water (hydrogen) content has a peak in the mantle transition zone. I will present a model to explain these observations assuming the whole mantle convection. A key is partial melting that likely occurs both above and below the transition zone. Partial melting at these depths promotes large scale transport of water and provides a mechanism to accumulate water in the transition zone and stabilizes the ocean mass.

Understanding volatile behavior, budget, and cycle in the mantle is one of fundamental questions in mantle geochemistry. In order to approach this issue, studies for volatiles on mantle-derived rocks, such as mid-ocean ridge basalts and ocean island basalts (OIB), have been conducted for decades. Overviewing the existing data of volatiles, OIB sourced from recycled mantle components show depletion in water relative to similarly incompatible trace elements, indicating water loss during slab subduction. However, F and Cl enrichment in some types of OIB suggests subduction transport of F and Cl. Carbon recycle is poorly understood because of low solubility of C in the melt, and therefore carbon in OIB should be a focus in the future studies.

Mo isotopic composition in volcanic rocks is recognized as a new geochemical tracer to understand the slab dehydration in subduction zones. Previous studies investigated Mo isotope systematics in northern Izu arc volcanoes including Izu Oshima, Niijima, Miyakejima, Hachijojima, and Izu Torishima. In this study, we measured the stable isotopic composition of Mo using TIMS for three basaltic xenoliths from Kozushima as well as basalts from Izu Oshima and Niijima.The samples from the fore-arc volcano (Izu Oshima) were found to possessδ⁹⁸/⁹⁵Mo＝0.13±0.09 ~ -0.11±0.09, whole those from back-arc volcanoes (Niijima and Kozushima) showed δ⁹⁸/⁹⁵Mo＝-0.27±0.09, δ⁹⁸/⁹⁵Mo =-0.15±0.07, which are consistent with previous studies [1]. However, the δ⁹⁸/⁹⁵Mo values is Kozushima samples were higher than those in Niijima, which is inconsistent with the correlation of major and trace element systematics. This suggests that the Kozushima samples may have been affected by factors other than the subduction process, such as secondary alteration.[1] Villalobos-Orchard, Javiera, et al. (2020): 68-82.

Since noble gases are chemically inert and their abundance ratios vary only by physical processes, compositional variations in volcanic gases are relatively simple. Variations in 3He/40Ar* ratios (40Ar* = 40Ar excess from atmospheric Ar) of fumarolic gases reflect variations in magmatic He/Ar ratios because both 3He and 40Ar* of fumarolic gases are mostly magmatic in origin. We have measured the concentrations and isotopic compositions of noble gases and CO2 of fumarolic gases collected on the north side of Mt. Shirane since 2015. As a result, the 3He/4He and 3He/CO2 ratios increased after May 2018, suggesting an increase in the supply of magmatic gas with high 3He/4He and 3He/CO2 ratios. The 3He/40Ar* ratios of the fumarolic gases significantly increased when the 3He/4He ratios were high. It has been suggested that He/Ar ratios in gas phases of magma increase with increasing magma vesicularity. Thus, the increase in the 3He/40Ar* ratios suggests an increase in magma vesicularity at the Kusatsu-Shirane volcano. In summary, 3He/40Ar* ratios of fumarolic gases might be an important indicator to evaluate a state of magma.

Groundwater and soil pollution of arsenic and mercury is reviewed in relation to the geologic cycle of these elements. The arsenic and mercury are transported into the crust, hydrosphere and atmosphere via magmatic and the following hydrothermal activities. Serious arsenic pollution occurred in the Quaternary sedimentary formations due to dissolution of volcanic ash and arsenic-bearing detrital minerals of magmatic and hydrothermal origins. As a volatile element, mercury emits along active faults. Mercury contamination of shallow groundwaters and soils is found on and near the boundary faults of Osaka Basin and the MTL at the south. The source of mercury would be deep fluid, such as Arima-type brine, since the contaminated areas coincide with the epicenters of deep low-frequency tremors.

The boron isotope ratios of the Taketomi submarine hot spring and the cuttings from Taketomi Island were measured respectively, and it was found that the equilibrium may have been reached at about 150°C. The sulfur hexafluoride concentration indicates that the residence time is about 20 years. The isotope ratios of water also suggested the existence of a reservoir where groundwater and deep-seated fluids are mixed.

We have collected hot spring water samples from the Tsugaru area of Aomori prefecture. The major inorganic components were analyzed and the results were plotted on the trilinear diagrams. A group, showing low pH, influenced by volcanic gases, were clearly identified by the plots are on the borders of the anion triangle and the key diagram. Most popular types of hot springs have an end member chemistry of so called fossil seawater, of which magnesium sulfate has been removed under high temperature and pressure and magnesium exchanged by sodium and potassium from underground water. Another end member chemistry is suggested as a ground water having high concentrations of calcium, sodium, and potassium carbonates. Major hot springs of the rest are explained as mixings of meteorological water having present sea water ionic ratio and various ground waters. These ground waters must have quite variable concentration ratios of alkali and alkaline earth elements. We are investigating the relationship of the chemistry and the location with geological settings.

Volcanic rocks of the Oman ophiolite include boninite, which is known to represent typical product of proto-arc magmatism. Thus, geochemical characteristics of such boninites and related volcanic rocks have a key to understanding slab-mantle interactions during subduction initiation. In this study, we present Sr, Nd, and Pb isotope compositions of Oman boninites and proto-arc tholeiites extruded prior to the boninites. The proto-arc tholeiites show isotope compositions consistent with melting of mantle metasomatized by slab fluids. On the other hand, boninite compositions require involvement of small amounts of slab melt as well as slab fluids. These isotope variations suggest involvement of hotter slab in boninite magma genesis than in proto-arc tholeiites, probably due to successive subduction of the slab after subduction initiation.

Lithium and its stable isotopes are key tracers of geofluids. This study tested if a cold-seep carbonate can be used as an archive of the Li isotopic composition of pore fluids, using a carbonate collected from a gas hydrate area of the Japan Sea. Calcium carbonate was sequentially leached with a weak acid, and Li was then purified from the leachates through ion chromatography. The Li concentrations and isotopic compositions measured for the leachates were interpreted to result from the mixing between Li in inorganic calcite and in secondary minerals. Endmember values of calcite were estimated and converted to the Li concentrations and isotopic compositions of the source fluids, using the partition coefficient and isotope fractionation factor. The resulting values were close to those measured for pore fluids in hydrate-bearing sediments of the same area.

Dimensional compression is an effective multivariate analysis technique that can find hidden structures when trying to simultaneously understand a large number of items that are difficult to intuitively understand. The chemical composition of geological samples collected in hydrothermal fields is considered to be an integral result of various geochemical processes. If we can extract and discuss these elements, we can expect to gain a better understanding of the various chemical processes in hydrothermal fields. The purpose of this study is to investigate the applicability of statistical methods to multi-element chemical composition data sets of geological samples collected over a wide area, with a view to understanding the behavior of trace amounts of useful metal elements. We performed principal component analysis and independent component analysis on the chemical composition data of geological samples collected from several hydrothermal activity areas in the Okinawa Trough and compared the results. As a result of the analysis, several elements were extracted that are considered to dominate the chemical composition, and there are components that broadly distinguish the mineral species in both methods. In the future, we would like to examine whether the parameters that characterize the behavior of useful metal elements can be found using these parameters.

Volcanic ash from the June 17, 1962 eruption of the Yakedake volcano was examined by microscopic observation, XRD, and water-soluble components analysis. As a result, pyrite fragments, gypsum, and relatively large amounts of water-soluble components (Cl, SO₄) were detected. These results indicate that this volcanic ash derived from a part of the hydrothermal alteration zone by a phreatic eruption, which supports the previous studies. On the other hand, a photomicrograph including pyrite fragments, the presence of gypsum, and a large amount of water-soluble components newly obtained in this study are presented here because they can be used as reference data in the case of future eruptions.

In order to understand the behavior of arsenic in magmatic fluid, concentrations of total and different chemical species of arsenic were quantitatively analyzed for the hydrothermal waters from the two phreatic eruption vents and low temperature spring water near the vents of Iwo-yama, one of the volcanoes of Kirishima. Total arsenic concentrations of hydrothermal waters from the two vents had been ＞3000 ppb for 22 months at the maximum after the eruption, then dropped to ＜500 ppb. Arsenite was dominant in the former high-arsenic containing waters, while arsenite and monothioarsenate were dominant in the latter low-arsenic containing waters. Arsenic concentrations of low temperature spring water were ＜80 ppb, and arsenate was the dominant species.Arsenite is the primary dissolved species of arsenic in the volcanic fluid of Iwo-yama. Presence of abundant elemental sulfur in the suspended matters and stoichiometric variation of arsenite and monothioarsenate suggest that the monothioarsenate was synthesized in the low-arsenic containing hydrothermal fluids trapped on the top of vents.

Radioactive materials are emitted from the Fukushima Daiichi Nuclear Power Plant (F1) in various chemical forms, such as gas, fine particles (solid), and ions (dissolved form). Among these, ultrafine particles (particles with a diameter of less than 1 µm) behave differently from ions and solids, and investigating the dynamics of ultrafine particles can provide new insights into the diffusion mechanism of radioactive materials. In this study, we attempted to develop an analytical method to measure the individual elemental composition of ultrafine particles at high-speed using ICP-MS combined with time-of-flight mass spectrometry (ICP-TOF-MS).The ICP-TOF-MS system used in this study (icp TOF R manufactured by TOFWERK) is capable of detecting Fe in stainless steel alloys and Zr in fuel cladding tubes, which are reactor materials, with high sensitivity, but there is a significant decrease in transmission efficiency for light elements such as B, which is a major component of control rods. In this presentation, we present the results of optimizing the analysis conditions (mainly ion lens operation conditions) to improve the transmission efficiency of B and individual elemental analysis of simulated debris particles composed mainly of B, Fe, and Zr.

Cosmogenic ¹⁰Be in natural samples is analyzed for a wide variety of applications in earth and planetary sciences. It has a long half-life (~1.4 Myr) and therefore should serve as a proxy of paleo-cosmic-ray variations during the past ca. 10 Myr. Recent improvements of the throughputs of ¹⁰Be and ⁹Be analyses enable us to obtain high-resolution time series of the Be isotopes from various paleo-archives. In this talk, I will present some recent developments in such studies aimed to elucidate paleo-cosmic-ray variations and synchronize multiple paleo-archives.

We have developed an in-situ uranium–thorium (238U–230Th) and uranium–protactinium (235U–231Pa) dating methods using multiple-spot femtosecond laser ablation-ICP-triple quadrupole-mass spectrometry (msfsLA-ICP-TQ-MS) for rapid age determinations of quaternary volcanic ash samples. In previous studies, in situ analysis of 230Th and 231Pa have been conducted by high-resolution sector field mass spectrometry, especially secondary ionization mass spectrometry (SIMS). However, SIMS requires a long-time measurement (10 minutes per sample). Because of this drawback, SIMS is not suitable for collection of chronological big data. In this study, msfsLA and ICP-TQ-MS were combined for the short-time measurement of 230Th and 231Pa (1 minute per sample). In the presentation, analytical accuracy and precision, and time required for measurements will be evaluated and the developed method will be applied to age determination of quaternary volcanic ash samples.

The isotope effect includes a mass-dependent effect and a non-mass-dependent effect caused by a nuclear volume effect, and in the non-mass-dependent effect, an odd-numbered mass-numbered isotope behaves differently from an even-numbered mass-numbered isotope. Isotopic anomalies (Ca, Ti, Cr, Sr, etc.) found in meteorites cannot be explained during nucleosynthesis, and features similar to the non-mass-dependent nuclear volume effect have been observed (Bigeleisen and Mayer,). 1947; Urey, 1947; Fujii, 1989). Solvent extraction shows similarities between the nuclear volume effect and the results of non-mass-dependent isotope fractionation (MIF) (Fujii et al., 2006), and the solvent is used to elucidate the isotopic anomalies found in meteorites. The extraction method is considered to be a useful experimental method. In this study, we focused on Sn, in which the influence of the nuclear volume effect is greatly observed in the solvent extraction method, and aimed to apply the information obtained there to the analysis results of Sn in iron meteorites.