The Okcheon metamorphic belt in South Korea has gained significant attention due to the widespread occurrence of black slates enriched in uranium and vanadium. This study aims to investigate the origin of black slate in the Boeun region by petrographic features and chemical properties. Based on the mineralogical composition and organic carbon concentration, the black slate was subdivided into coaly slates. Within these coaly slates, the sulfide veins contain diverse sulfide species resulting from the mixing of magmatic hydrothermal fluids and seawater. Additionally, these veins have undergone hydrothermal alteration. Moreover, noteworthy concentrations of uranium (average: 66 ppm) and vanadium (average: 0.9%) was detected within the coaly slate. The formation of dominant uranium minerals, such as uraninite, is associated with quartz, sulfides, phosphate minerals (e.g., xenotime, monazite, apatite), coal material, and muscovite. Uranium accumulation exhibits positive correlations with total sulfur (TS), phosphorus pentoxide (P2O5, total organic carbon (TOC), and total iron (Fe2O3) contents. Moreover, they are genetically associated with redox-sensitive elements such as Mo, V, Zn, Ni, Co, and Cu. In the case of muscovite within the coaly slate is considered a primary source of vanadium (average: 1.6%) and displays positive correlations with total nitrogen (TN), aluminum oxide (Al2O3), gallium (Ga), niobium (Nb), zirconium (Zr), chromium (Cr), and rare earth elements (REE) contents. The isotopic signatures of carbon, nitrogen, sulfur, and iron in the study area suggest that the accumulation of uranium and vanadium in the coaly slate was facilitated within a submarine hydrothermal environment.

Slow earthquakes that occur at the subduction plate boundary are of great importance, including their close relationship to the large earthquakes. Although it is still unclear what geological process is related to the slow earthquakes, it is believed that fluid-rock interactions are important for their occurrence. Deep slow earthquakes that occur at greater depths beyond the seismogenic zone in subduction zones such as SW Japan may be associated with high-temperature fluid-rock interactions, and can be studied using geochemical approaches. We show that the Arima-type deep fluids can be candidates for such slow earthquake-related fluids, as some of them are observed in the region under which deep slow earthquakes frequently occur. We also show preliminary results that mélange rocks of the Shimanto accretionary complex, which have been proposed to represent the deep slow earthquake-related rocks, have geochemical characteristics consistent with high-temperature fluid-rock interactions at >300 deg. C.

Recently, Mo isotope ratios in subduction zone volcanic rocks have been studied in a number of volcanic arcs to understand the recycling of subducted material in subduction zones. However, the processes that control the variations in Mo isotope ratios in rocks samples from the rear arc (RA) region remain unclear. The Northeast Japan (NE Japan) has many volcanoes from the volcanic front (VF) to the region of the RA, and is a suitable for comparing changes in geochemical composition along with the slab depth of each volcano. In this study, we measured Mo isotopic compositions of Kampu and Sannomegata in the RA volcanoes of NE Japan and compared them with previous studies. Samples from Kampu showed relatively low Mo isotope ratios similar to the other RA volcanos (Chokai, Iwaki) in the NE Japan (-1.20 to -0.29; N = 5), while those from Sannomegata showed Mo isotope ratios similar to those of VF in the NE Japan (+0.35 to +1.83; N = 3). The samples from Kampu have relatively high SiO2 abundances (53.0 to 63.8%), which may have been influenced by differentiation including hornblende. The low SiO2 abundance (48.1 to 51.6%) of the samples from the Sannnomegata, which are very close to those of primary magma, but with significantly larger Mo isotope ratios than DM and other magmas, require further investigation.

Knowing where magma and groundwater are located and in what state they exist is highly important to understand volcanic activity. We investigate the distribution of electrical resistivity within the volcanic edifice and are trying indirectly to know the difference in constituent materials or in the state. So far, we have clarified the shallow resistivity structure of volcanoes that have repeated phreatic eruptions from dense electromagnetic surveys around the active crater. As a result, hydrothermally altered, poorly permeable rock layers (cap rocks) with low resistivity values and areas with rather high resistivity values beneath them were commonly detected in shallow areas. We believe that the area showing this slightly high resistivity value is a gas reservoir, and could be a preparation zone for a phreatic eruption. In addition, at the Kusatsu-Shirane volcano, we have succeeded in imaging the high salinity region that developed above the deep partially molten region. Multiple low-permeability barriers are thought to control volcanic activity.

Recycling ages of oceanic crusts are determined by combining Pb and Nd isotopic composition of OIB (ocean island basalts) to constrain time-scale of material cycle in the Earth.

Isotopic variations in ¹⁸²W result from the fractionation of Hf and W that occurred during the existence of ¹⁸²Hf, which has a short half-life. Since Hf and W are lithophile and siderophile, respectively, Hf is thought to remain in the silicate melt phase and W in the molten metal phase during earth core formation. As a result, the initial mantle is thought to have high W isotopic ratios, and the metallic core is thought to have low isotopic ratios. After that, late veneer with low W isotopic ratios are thought to have lowered the W isotopic ratios in the mantle to the present values in the upper mantle.In this study, we investigate the Hf-W partitioning between silicate melts and molten iron using ab initio free energy calculations under high temperature and pressure conditions, which are difficult to achieve in laboratory experiments. We also calculated whether the partition coefficient changes when iron is mixed with silicate and vice versa. It was confirmed that W remained siderophile and Hf remained lithophile in both cases. Based on these results, clarifying the W isotope evolution is necessary.

This study presents new geochemical and petrological data from the Higashi-Matsuura alkali basalts and demonstrates the presence of a LOMU-type mantle in southwest Japan. Radiogenic isotope ratios measured at the Hiroshima University (TIMS MAT-262) show low 206Pb/204Pb ratios (17.72 - 18.04) and moderate 87Sr/86Sr ratios (0.7041- 0.7044), indicating similarities with LOMU-type alkali basalts found in East Asia (e.g., Changbaishan, Wudalianchi, Xiaogulihe etc.).Petrological studies indicate that primary magma was generated in the hydrous asthenospheric mantle. Previous studies established that a hydrous asthenospheric mantle (> 1.8 GPa) derived from the stagnant Pacific Plate was responsible for the origin of southwest Japan alkali basalts. However, this model cannot explain LOMU-type isotopic ratios of Higashi-Matsuura basalts.In this study, we modelled the lead isotopic evolution for the generation of LOMU-type magmas, suggesting mixing of two independent Paleoproterozoic magma sources.

Nitrogen is one of the most significant volatiles in the Earth, an essential element for life, and the primary component of the atmosphere. The Earth's missing nitrogen problem is manifested by an extremely low nitrogen concentration and a super-chondritic C/N ratio of the bulk silicate Earth (BSE). Understanding the nitrogen depletion in the BSE is a key to the storage and isotopic features of nitrogen in Earth's deep reservoirs as well as the delivery process of volatiles to the early Earth. Core-mantle differentiation is one of the most significant processes controlling the initial distribution of elements in the early Earth. Knowledge of the partitioning behavior of nitrogen during the core-mantle differentiation is therefore of fundamental importance to the Earth's nitrogen budget and subsequent evolution. In this study, we perform ab initio molecular dynamics combined with the thermodynamic integration method to calculate partition coefficients of nitrogen between iron and silicate melts to 135 GPa and 5000 K. Our results demonstrate that nitrogen basically remains siderophile under high-pressure and temperature condition irrespective of its different chemical speciation, and predict a positive but nonlinear effect of pressure on nitrogen partitioning, which is primarily caused by the structural modification of the silicate melt upon compression. Combining first-principles calculations with geochemical modelling, we find that the BSE can be extremely depleted in nitrogen if nitrogen undergoes deep core-mantle differentiation. These results provide important constraints on the distribution of nitrogen in the deep Earth and offer new insights into the delivery of volatiles during the proto-Earth growth.

Noble gases are chemically inert and their behavior is not always similar to those of the other elements. Their isotope ratios also reflect such effects as mass fractionation, addition of radiogenic and nucleogenic isotopes as shown in the difference between those of MORB and OIB. Further, relative abundances of primorodial components such as ³He differ between MORB and OIB, reflecting the evolution of the Earth. Noble gases have been considered to be retained mostly in the silicate phase in the interior of the Earth.In recent years, however, it has been argued that ³He might be retained in the core. But there are no trial to explain the state of heavier noble gases including Xe from such a point of view. In my talk, I will discuss the problems of the sate of noble gases in the Earth's deep interior and its relationship with the evolution of the Earth, referring the recent publications.

We analyzed noble gas isotopes of mantle xenoliths from Oahu Island, Hawaii. They show plume-like isotopic signatures, suggesting that the mantle xenoliths in OIB serve as storage vessels transporting plume-derived magma without contamination from surface materials.

Understanding the structure and evolution of the oceanic plate and the upper mantle is important for understanding the earth's material circulation and global inner earth system. The purpose of this study is to estimate elemental transfer at the crust-mantle boundary and melt extraction ages of the upper mantle to analyse siderophile platinum group elements (PGEs) and Os isotope compositions using samples from the CM site of the Oman Drilling Project, which directly drilled the crust-mantle boundary. The data from the harzburgites of the CM site show flat PGE patterns and low Os isotope ratios. On the other hand, dunite shows a large variation in all PGEs and a relatively high Os isotope ratio, suggesting melt coexistence. Combining the results of the gabbro, which forms the lower crust, we will compare the crust-mantle boundary materials.

Ultramafic rocks are present in a variety of tectonic settings on Earth.We believe that the origin and history of ultramafic rocks can provide information on the processes of partial melting and melt migration and extraction in the mantle and on the tectonic evolution of geologic units containing ultramafic rocks. In the presentation, however, we would like to share our experience that natural samples should be carefully examined to determine where and how they were formed.

We conducted oxygen and hydrogen isotope measurements of clay mineral in a sediment core obtained from an active hydrothermal filed in the Okinawa Trough, in order to estimate subseafloor thermal gradient based on isotope geothermometry. We found very steep thermal gradient up to 20 degree/meter at the upper most layer of the altered zone.

Hydrothermal discharge is still continuing at the April 2018 crater at Ioyama volcano of the Kirishima Volcanic Group (Kyushu, Japan). Hyper-acidic Cl-type hydrothermal fluids with negative pH and a dissolved Cl concentration exceeding 100,000 mg/L were observed after May 2023. Such hydrothermal fluids in the craters have a flat slope of about 2.3 on the dD-d¹⁸O diagram, and some of them show heavier dD and d¹⁸O values than those of magmatic vapors. Therefore, these hyper-acidic hydrothermal fluids are considered to be enriched in D, ¹⁸O, or dissolved H⁺ and Cl^- by evaporation at the crater site.

In this study, we proposed a machine learning method that can analyze a dataset of river sediments covering geological chemical composition data from all over Japan and tsunami deposit samples that have been accumulated so far, and analyzed them using specific samples. The samples used in the analysis were a sample identified as a muddy tsunami deposit, a sample identified as a sandy tsunami deposit, and a river deposit sample treated as a terrestrial deposit in the eastern and central Japan. The data were output as two-dimensional scatter plots by using PCA and UMAP, which are dimensionality reduction methods. The data were qualitatively evaluated by looking at the arrangement of the clusters and which of the clusters in the data set was closest to the tsunami deposit data. The results show that in the strata that contain a single layer of sandy tsunami deposits and no flood deposits, the dimensional compression of the compositional data clearly shows deposits with compositions similar to those of sandy tsunami deposits.

This study focused on developing a method for analysing the oxygen isotope ratio of calcium carbonate in otoliths and other microdomains. The isotope ratios of calcium carbonate varies on the micrometre order even within single crystals. Therefore, we set out to develop a method for analysing oxygen isotope ratios in the micro-region. We focused on microscopic Raman spectroscopy, which has excellent spatial resolution and is non-destructive. There have been no examples of isotope ratio analysis using Raman spectroscopy so far, and most of them have been limited to isotope qualification. In this study, errors in the oxygen isotope ratio of calcium carbonate are investigated from Raman spectra and the potential for natural applications is discussed.

This study provides a new idea on data processing by correcting the linear relationship between the absorbance and sample concentration according to the Beer-Lambert law using the least absolute deviation (LAD) method to exclude the effect of random noise on the data fit. The spectrum resolution in this study is 0.4 cm^-1. Instrument optics and Fast Fourier Transform (FFT) setups were optimized for high-resolution measurements. The UV absorption cross-section of each SO₂ sulfur stable isotopologue was presented and the isotopic effect was also discussed. In addition, the raw interferograms were recorded, where the FFT can be applied to generate lower-resolution spectrums. Therefore, the relationship between spectrum resolution and the isotopic effect was discussed.

Remarkable progress has been made in cosmochemical studies using precise Cr isotope analysis. In Cr isotope measurements by TIMS, the ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr ratios are obtained by correcting for mass fractionation using a constant ⁵⁰Cr/⁵²Cr ratio. However, a linear correlation has been observed between the ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr ratios after mass fractionation correction, with a slope of mu⁵⁴Cr/mu⁵³Cr = ~2. In this study, the residual isotopic fractionation was evaluated by repeated measurements of Cr standards using TIMS. Data were acquired by the 3-line multistatic method and compared with analyses by Re and W filaments. The residual isotope fractionation was confirmed in both analyses, but the slopes of the correlations were different: mu⁵⁴Cr/mu⁵³Cr = 1.93 for Re filament and 1.08 for W filament. The ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr ratios were several times more precise for W than for Re filament measurements. This difference is attributed to the fact that the Re filament temperature during analysis was about 100 ^oC higher than that of W, resulting in the formation of Cr oxides. In Cr isotope analysis by TIMS, it is important to use W filaments and operate at a lower temperature to suppress oxide formation as much as possible in order to improve the precision.

Ships are still important platforms for research and observation at sea, even though various unmanned and automatic observation equipment is in practical use at present. In Japan, institutional systems for shared use of research vessels have been developed and are being used. Given the nation's fiscal situation, however, we are facing increasing constraints on the research use of public vessels. Since various institutions in Japan own and operate "training vessels" for the purpose of training navigation officers and crew members, research use of these vessels may alleviate the constraints on research vessel operation. In this presentation, I will summarize the current situations of training vessels from the perspective of their use for research purposes.

Tokyo University of Marine Science and Technology has three training ships, among which the navigation conducted by the Faculty of Marine Life Science and the Faculty of Marine Resources and Environment mainly involves practical training for maritime officer. In recent years, these voyages have been joined by various research, providing students with opportunities to engage in cutting-edge marine research. In the future, it will be necessary to expand the use of training ships by participating in various researches on training cruises. On the other hand, securing human resources and time to respond to such needs has emerged as a new issue.

In this presentation, we will present the marine research using the training vessel "Toyoshio-maru" of the Hiroshima University, especially for the environmental changes of the Hiroshima Bay in the last three decades. Secchi depth will be controlled by the suspended particles in the water, especially soil, chlorophyll and/or phytoplankton biomass. Their relationship with primary production should be an important factor in coastal marine environments. In this presentation, we present the Secchi depth data obtained in the Hiroshima Bay in the last three decades by using "Toyoshio-maru". The Secchi depths in the whole station in the Hiroshima Bay tended to be increased during recent 30 years. Similar increases in the Secchi depth have been reported in Osaka Bay, Harima Bay, and Suo Nada. This may be one of the evidence of recent oligotrophication of the Seto Inland Sea. In this presentation, we will discuss the relation between Secchi depth and photon intensities under water.