Laura KOTOMAA¹, Markku VÄISÄNEN² , Jussi S. HEINONEN^1,3, Ermei MÄKILÄ⁴ ,Hugh O’BRIEN⁵, and Arto PELTOLA²
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70049]
¹Geology and Mineralogy, Abo Akademi University, Turku, Finland
²Department of Geography and Geology, University of Turku, Turku, Finland
³Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland
⁴Department of Physics and Astronomy, University of Turku, Turku, Finland
⁵Geological Survey, of Finland, Espoo, Finland
Published by arrangement with John Wiley & Sons

Löpönvaara is a rare new phosphorus-rich iron meteorite find from Löpönvaara, Finland. The ~164 g meteorite was discovered in 2017 from the same area as the ungrouped Lieksa pallasite. Löpönvaara was classified as an ungrouped iron meteorite due to its unusually high concentration of P (>4 wt%), coupled with a moderate concentration of Ni (~11 wt%), and Ga–Ge abundances in the “III” range. The meteorite consists of ~75 vol% kamacite and ~22 vol% schreibersite, with accessory troilite (<0.1 vol%), and minor terrestrial weathering products. The kamacite in Löpönvaara occurs as three different types: (1) rare, large 2–5 mm partially resorbed clasts; (2) round, ≤0.5 mm partially resorbed clasts; and (3) small, several tens of μm to sub-μm exsolution blebs and globules in the matrix. Schreibersite occurs solely as microscopic matrix material in between the type (1) and (2) kamacite clasts. The lack of taenite and the overall compositional and textural features of Löpönvaara suggest that it retained its composition possibly from a P-rich portion of immiscible melt at late stages of fractional crystallization, but its textural features suggest that the meteorite suffered impact-related metamorphism. The meteorite has no close textural or compositional affinities, which makes it unique and an important target for future studies.

Rei KANEMARU¹ et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70045]
¹Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Kanagawa, Japan
Published by arrangement with John Wiley & Sons

Silica polymorphs in meteorites provide critical constraints on crystallization processes associated with thermal activity in the early solar system. A detailed investigation of silica polymorphs in eucrites (the largest group of achondrites) using cathodoluminescence imaging and laser-Raman spectroscopy revealed significant variations in the relative abundance of silica polymorphs. Based on these variations, the eucrites were divided into four “Si-groups” according to their dominant silica phase: Si-0 (cristobalite-dominant eucrites), Si-I (quartz-dominant eucrites), Si-II (quartz and tridymite-dominant eucrites), and Si-III (tridymite-dominant eucrites). In studied eucrites, tridymite and cristobalite form lathy euhedral shapes, while quartz is anhedral, coexistent with opaques and phosphates, suggesting that silica polymorphs were crystallized from different stages and formation processes. We propose a new model that explains the formation pathways of silica minerals in eucrites and accounts for the distinct formation histories represented by each Si-group: tridymite crystallizes from alkali-rich immiscible melts (starting at ≥ ~1060°C), cristobalite crystallizes from quenched melts (~1060°C), and quartz crystallizes from extremely differentiated melts and/or by solid-state transformation from tridymite and cristobalite through interactions with sulfur-rich vapor below ~1025°C. This model explains the occurrences of silica polymorphs in eucrites without requiring secondary heating or shock processes.

Megan Broussard^a, Mason Neuman^a, Piers Koefoed^a, Frédéric Moynier^b, Nicole X. Nie^c, Richard V. Morris^d, Bradley L. Jolliff^a, Kun Wang^a

Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.09.004]
^aDepartment of Earth, Environmental, and Planetary Sciences and the McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
^bUniversité Paris Cité, Institut de Physique du Globe de Paris, CNRS, UMR 7154, F-75005 Paris, France
^cDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
^dAstromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX 77058, USA
Copyright Elsevier

As a part of the Apollo Next Generation Sample Analysis Program, we report the Cu and Zn isotopes in the Apollo 17 regolith core, double-drive tube 73001/2. The intervals in the upper core, which sampled the regolith closest to the lunar surface, are enriched in heavy Cu and Zn isotopes compared to the deeper intervals. The top 2 cm have a δ⁶⁵Cu value of 2.85 ± 0.01 ‰ and a δ⁶⁶Zn value of 5.54 ± 0.02 ‰. The intervals become lighter in isotopic composition to a depth of 8 cm. Below this depth, the average δ⁶⁵Cu is 1.02 ± 0.08 ‰, while the average δ⁶⁶Zn is 2.27 ± 0.24 ‰. We find strong correlations between the isotopic fractionations of Cu and Zn and the maturity index I_S/FeO. These correlations in the core result from a binary mixing between highly space-weathered soil at the lunar surface and deeper, shielded soil, with isotopic fractionation occurring at the surface due to space weathering and soil mixing occurring due to impact gardening. Using the K, Fe, Cu, and Zn isotopes measured in 73001/2, we find a strong correlation between the degree of isotope fractionation and volatility. We model the isotopic fractionation of K, Fe, Cu, and Zn by space weathering in lunar soils using mass balance equations between the lunar atmosphere and lunar soil and find agreement with the fractionation observed in 73001/2. Using the fractionation observed in 73001/2, we present a new exposure age model using Cu isotope fractionation in lunar soils.