¹E. Dobrică, ²J.P. Greenwood, ¹A.N. Krot, ³A.J. Brearley, ⁴E.P. Vicenzi, ⁵S. Itoh, ⁶N. Sakamoto, ⁷H. Yurimoto
Geochimica et Cosmochimica Acta (in Press) Link to Article [DOI: 10.1016/j.gca.2026.08.009]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, HI, USA
²Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT, USA
³Department of Earth and Planetary Sciences, University of New Mexico, NM, USA
⁴Smithsonian Institution, Museum Conservation Institute, Suitland, MD, USA
⁵Division of Earth and Planetary Sciences, Kyoto University, Kyoto, Japan
⁶Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo, Japan
⁷Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
Copyright Elsevier

Hydrogen isotopes in apatite are widely used to constrain the origin and evolution of water in Martian magmas and crustal reservoirs. However, the extent to which shock metamorphism modifies hydrogen-isotope compositions in apatites is poorly understood. In this study, we combine scanning electron microscopy (SEM), cathodoluminescence (CL), transmission electron microscopy (TEM) observations, and secondary ion mass spectrometry (SIMS) measurements of hydrogen isotopes and water contents in apatites from the Martian meteorite Los Angeles. Panchromatic CL imaging reveals distinct bright and dark domains within individual apatite grains. These domains correlate with variations in hydrogen-isotope composition, chlorine abundance, and shock metamorphic microstructures (dislocations, planar fractures, and shock-induced melting) observed at the nanoscale. Bright CL regions show higher defect densities, more abundant melt pockets, lower chlorine contents, and elevated δD values relative to dark CL regions. Defect density correlates positively with δD and melt pocket abundance but shows no systematic relationship with bulk H₂O content. These observations demonstrate that hydrogen-isotope modification can occur in heavily deformed apatite without requiring complete melting or recrystallization. Shock-induced defects therefore provide pathways for hydrogen redistribution and isotopic exchange at the micron scale. The results indicate that shock metamorphism can locally modify primary hydrogen isotope signatures in Martian meteorites while preserving bulk water contents within the typical Martian apatite range. Cathodoluminescence imaging provides a rapid and non-destructive method for identifying apatite domains that can correlate with deformation-enhanced and isotopically-modified regions. These findings have important implications for interpreting Martian volatile reservoirs and for future sample-return missions such as Martian Moons eXploration (MMX).

¹Shiori Inada, ^1,2Shogo Tachibana
Geochimica et Cosmochimica Acta (in Press) Open Source Link to Article [DOI: 10.1016/j.gca.2026.07.046]
¹Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan
²UTokyo Organization for Planetary and Space Science, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan
Copyright Elsevier

Effects of ambient gas are important for understanding evaporation of planetary materials in the protosolar disk. In this study, we experimentally investigated the evaporation kinetics of forsterite in H₂-H₂O gas mixtures to elucidate the dependences on H₂O abundance at  of 10⁻⁴–10⁻², temperatures of 1400–1600 K, and a total pressure of 1 Pa. We found that the evaporation rate decreases with increasing  with a reaction order of −1.02 ± 0.12 only above certain  (10⁻³–10⁻² depending on temperature). The activation energy increased when the evaporation is suppressed by H₂O (497 ± 11 kJ mol⁻¹, while 359 ± 1 kJ mol⁻¹ without the effect of H₂O). The  dependence of the evaporation rate is consistent with the previously proposed model based on the chemical equilibrium consideration and the Hertz-Knudsen equation. This consistency can be explained in terms of a reaction mechanism. Based on the experimentally determined evaporation kinetics, we evaluated conditions of the protosolar disk where H₂O affects evaporation of forsterite dust. This showed that H₂O suppresses the evaporation at 1300 K at  of the Solar abundance and 1600 K under H₂O-enriched conditions, which possibly affected moderate-temperature thermal processing of silicate dust and evaporation of chondrule melt under oxidizing conditions.