The whole-rock composition of peridotites is essential for understanding geological processes related to the Earth’s mantle. X-ray fluorescence (XRF) analysis employing glass beads is the most common method to determine the chemical composition of igneous rocks because of its simplicity and efficient decomposition of refractory minerals. The accuracy of the XRF analysis using a multipoint calibration curve depends on the matrix effects and the reference values in the reference materials (RMs) used. In the quantitative analysis of peridotites, the limited availability of certified ultramafic RMs necessitates the incorporation of other igneous rocks into the calibration curve (along with a small number of ultramafic RMs), leading to potential systematic biases. In this study, we propose a robust approach to obtain accurate major element concentrations in ultramafic rocks. Specifically, we examine (1) the difference in the X-ray fluorescence intensity of total iron (T-Fe₂O₃) relative to the concentration between peridotite and other igneous rocks, and (2) the selection of the reference values in RMs for the quantification of Cr₂O₃. We found that the matrix correction using Ca and Mg improves the T-Fe₂O₃ calibration curve, and the quantified T-Fe₂O₃ concentrations of peridotite and basalt using the corrected calibration curve are consistent with the certified values in RMs. T-Fe₂O₃ concentration in peridotite could be overestimated by ~0.5–0.6 wt% without matrix correction. In contrast, NiO and other major elements exhibit minimal matrix effects; the accuracy of their calibration curve depends on the variation of reference values in RMs. For Cr₂O₃, peridotite RM JP-1 is the most critical because of its highest Cr concentration among the calibration standards, and its recent analyzed value provided by the Geological Survey of Japan (GSJ) was used to optimize the accuracy of the calibration curve. The proposed correction of matrix effect and reference values in RMs in the analysis of peridotite enhances quantification accuracy and improves our understanding of the Earth’s mantle geochemistry.

The concentrations and isotope ratios of molybdenum (Mo) and tungsten (W) are expected to serve as proxies for paleoceanography. Although submarine hydrothermal activities are potentially major sources and sinks of Mo and W, data on these elements in hydrothermal fluids are scarce. In this study, we present the concentrations and isotope ratios of dissolved Mo and W in hydrothermal fluid samples collected from nine active sites—Higashi Ensei, Iheya North, JADE, Hakurei, Higashi Izena, Daisan Kume, Yokosuka, Futagoyama, and Hatoma Knoll—within the Okinawa Trough, which is a back-arc basin. The Mo concentrations ranged from 4.2–411 nmol/kg, δ^98/95Mo values ranged from –0.17 to 3.92‰, W concentrations ranged from 1.7–238 nmol/kg, and δ^186/184W values ranged from –0.03 to 1.08‰. We found that both δ^98/95 Mo and δ^186/184W were close to 0‰ when Mo and W were dissolved from rocks and sediments during hydrothermal circulation. The phase separation of the hydrothermal fluids concentrates Mo and W in the liquid phase. Sediments can be a significant source of W at high temperatures and Mo even at low temperatures. The scavenging of Mo by Fe sulfides reduces its concentrations and elevates δ ^98/95Mo values during the emission of high-temperature hydrothermal fluids, while having an insignificant effect on W. The scavenging of W by Fe hydroxides reduces its concentrations and elevates δ ^186/184W values during mixing of hydrothermal fluids and seawater, while having an insignificant effect on Mo. Therefore, the data on Mo and W are useful for investigating the processes that occur during hydrothermal circulation.

We report five new igneous rock reference materials: andesite JA-2a, granite JG-2a, granodiorite JG-3a, gabbro JGb-1a, and peridotite JP-2. JA-2a, JG-2a, JG-3a, and JGb-1a are new reference materials prepared from the same parent rocks as JA-2, JG-2, JG-3, and JGb-1, respectively; the ultramafic JP-2 was newly prepared from plagioclase lherzolite. These certified reference materials were prepared according to the ISO 17034-certified procedures. The certified values of these new reference materials were determined for SiO₂, TiO₂, Al₂O₃, T-Fe₂O₃, FeO, MnO, MgO, CaO, Na₂O, K₂O, P₂O₅, and H₂O (−) (moisture content) based on the collaborative analysis. The chemical compositions of the new reference materials, JA-2a, JG-2a, JG-3a, and JGb-1a, are consistent with those of JA-2, JG-2, JG-3, and JGb-1, respectively. JP-2 exhibits higher Al₂O₃, CaO, TiO₂, Na₂O, and SiO₂ and a lower MgO mass fractions than those of dunite JP-1. This can expand the petrological and chemical diversity of ultramafic rock reference materials, which are a very rare variety worldwide.

Detecting seawater-derived elements in terrestrial sediments as evidence of tsunami inundation is challenging due to dilution by freshwater over time. This study provides data useful for evaluating the potential of the strontium (Sr) isotope ratios (⁸⁷Sr/⁸⁶Sr) as indicators of seawater intrusion. We analyzed ⁸⁷Sr/⁸⁶Sr ratios in water leachates and acetic acid (AcOH) leachates from a sedimentary sequence sampled in November 2015 from a coastal lowland in Tohoku, Japan, which includes deposits from the March 2011 Tohoku earthquake tsunami. The ⁸⁷Sr/⁸⁶Sr values of water leachates were low (~0.7082) in the pre-tsunami muddy layer, close to local freshwater values (0.7069), but higher (~0.7085) in the upper muddy part of the tsunami deposit, approaching seawater values (0.7092). This suggests that the muddy part retained seawater-derived Sr due to its low permeability and high cation adsorption capacity of clay minerals. However, alternative sources of high Sr isotope ratios, such as rainwater, atmospheric deposition, and acid-leachable materials, must be considered. If the high values reflect seawater intrusion, Sr isotope ratios provide a distinct advantage over element concentrations as tsunami indicators due to their longer retention, detectable even four years after the event. In contrast, AcOH leachates exhibited significantly higher Sr isotope ratios (>0.7095) throughout the sequence, perhaps reflecting contributions from less-soluble components, such as oxides and clay minerals, in addition to marine carbonates. This finding suggests that AcOH leaching is unsuitable for isolating seawater-derived Sr.

We report the occurrence of glimmerite and melteigite xenoliths from a hybrid Early Cretaceous camptonite - tinguaite dyke from the Nongchram fault zone, East Garo Hills, Shillong Plateau, North East India. Glimmerite xenolith contains predominantly biotite with subordinate to minor amounts of pyroxene, ferro- dolomite, rutile, and ilmenite. The melteigite xenolith is dominated by pyroxene and contain pseudo-nepheline (altered to analcime) and rutile. The host campto-tinguaite dyke features a distinctive porphyritic-panidiomorphic and a tinguaitic texture with clinopyroxenes as macrocrysts, microcrysts and clots and amphibole as phenocrysts with accessory minerals such as apatite, magnetite, rutile, and ilmenite. In-situ trace element geochemistry of pyroxenes from the xenoliths and the host rock reveals significant enrichment in LILEs such as Ba and Sr, as well as LREEs like La and Ce, suggesting an enriched mantle source. The geothermobarometric data for pyroxenes from the (i) glimmerite and melteigite xenoliths and macrocrysts and (ii) microcrysts and clots from the campto-tinguaite suggest varying crystallization pressures and temperatures, indicating different depths of origin ranging from 23 - 96 km. The mineral composition, in-situ trace element data of pyroxenes as well as the geothermobarometric study of clinopyroxenes from both the host and the xenoliths, suggest involvement of multiple shallower magma chambers composed of the camptonitic and tinguaitic magmas generated during distinct pulses, thereby forming a complex magmatic plumbing system. The presence of orogenic geochemical signatures in the minerals of xenoliths and anorogenic geochemical signatures in the host campto-tinguaite pyroxenes imply a complex tectono-magmatic setting, with contributions from both the plume and subduction-modified mantle sources.