Analytical solutions are proposed predicting the change in concentration and in isotopic composition of trace elements in magmatic liquids evolving by concurrent processes of fractional crystallization and wallrock assimilation (AFC), in the case the concentration of the trace element in the assimilate is assumed to change according to Shaw’s (1970) model of fractional melting of the wallrock. This particular AFC model, was first suggested and numerically approached by Spera and Bohrson (2001) in their energy-constrained AFC model (EC-AFC), without however giving analytical solutions.

The solutions here proposed are ‘natural extensions’ of the simpler solutions given by DePaolo (1981) and by Taylor and Sheppard (1986), turning to them if the distribution coefficient of the trace element between bulk residual wallrock and instantaneous melt is 1. However, as also shown by Bohrson and Spera’s calculation examples, these solutions generally predict concentration and isotopic evolution paths which are very different from those predicted by DePaolo’s and Taylor and Sheppard’s model. This is because, in addition to the trace element distribution coefficient between the residual solid and the instantaneous melt produced by melting of the wallrock, the analytical solutions contain a new parameter, which is the mass ratio between the initial magmatic liquid and the wallrock involved in the melting process.

Water ice trapped in permanently shadowed regions (PSRs) near the lunar poles is an important research target for understanding the distribution of light elements in the Moon. Herein, we examined the relationship between the near-infrared water absorption band depth and water ice content in mineral powders with a low ice content; these minerals serve as analogs to the regolith in the lunar PSRs. Four base minerals—olivine, plagioclase, clinopyroxene, and a mixture of these—were prepared at two grain size fractions. We constructed calibration lines based on the correlation between the water ice content ranging from 0.3 to 2.2 wt.% and 1.5-μm water absorption band depth. Results show that the calibration-line gradients, which are key parameters for determining the water ice content based on the absorption band depth, depend on the mineral species and grain size. The calibration-line gradients increased with increasing mineral grain size and correlated with variations in 1.5-μm reflectance among the dry mineral samples. The calibration-line gradients and reflectance values decrease in the order of clinopyroxene, plagioclase, mixture, and olivine. Combining the effects of mineral reflectance and grain size, we establish a predictive relationship for estimating the water ice content based on the observed 1.5-μm absorption bands. The proposed relationship provides a practical method to determine the ice content for future in situ landing explorations of the lunar PSRs, even when the exact regolith composition is unknown.

Drifting pumices provide important clues for determining the activity of submarine volcanoes. On October 8, 2023, a tsunami hypothetically caused by a submarine eruption occurred near Izu-Torishima in the Izu-Bonin Arc. Later that month, two types of drifting pumice, white and gray, were found floating on the sea surface west of Izu-Torishima. The white pumices were also found on the coast of Izu-Torishima. The textural and geochemical characteristics of the gray pumice clasts indicate they were derived from the 2021 eruption of Fukutoku-Oka-no-Ba. The white pumice clasts have angular to subangular shapes with little evidence of abrasion. They contain plagioclase, pyroxenes, and Fe-Ti oxides as phenocrysts, and typically include dark enclaves. The composition of the white pumices is rhyolite to dacite, and their trace element characteristics resemble those of volcanic products from the back-arc rift zone of the Izu-Bonin Arc. These pumices are potentially associated with a recent submarine eruption in the back-arc region of the Izu-Bonin Arc.

Hydrous alteration of ultramafic rocks produces unique reducing environments accompanied by hydrogen (H₂) generation. To understand the early stages of the reaction, batch experiments were conducted at 90°C for 2 weeks using a NaNO₃ solution, natural dunite and harzburgite samples with variable degrees of serpentinization. Our results indicate that the fresh ultramafic rocks generate more H₂ than serpentinized rocks, showing that the dissolution of major minerals in fresh ultramafic rocks (i.e., pyroxene and olivine) is the dominant factor in H₂ generation. Fresh harzburgite yielded higher amounts of H₂ of up to 322.1 μmol/kg than the other ultramafic rocks. Fresher samples had higher dissolved Si and Ca concentrations in the solutions with higher H₂ generation than the serpentinized samples, which can be explained by the dissolution of pyroxene, because the main host mineral for Ca is clinopyroxene. Magnesium-bearing silicates were observed in the experiments using a fresh harzburgite, probably due to the more effective Si supply from pyroxene dissolution than olivine. Another series of experiments using a fresh harzburgite with different chemical reagents showed that the addition of Si enhanced H₂ generation, suggesting that H₂ generation was regulated by the precipitation of magnesium silicate hydrate. Thermodynamic calculations indicated that the solution chemistry during the hydration of fresh ultramafic rocks was regulated by magnesium silicate hydrate, whereas the solution chemistry during the hydration of serpentinized rocks was buffered by brucite. Our study suggests that fresh harzburgite is more favorable for H₂ generation than dunite at 90°C because of its higher pyroxene content.