¹Baptiste Le Bellego, ¹Célia Dalou, ¹Béatrice Luais, ²Pierre Condamine, ³Vincent Motto-Ros, ¹Laurent Tissandier
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.11.038]
¹Université de Lorraine, CNRS, CRPG, F-54000 Nancy, France
²Laboratoire Magmas et Volcans, Université Clermont Auvergne, CNRS UMR 6524, OPGC-IRD, F-63000 Clermont-Ferrand, France
³Institut Lumière Matière UMR 5306, Université Lyon 1 – CNRS, Université de Lyon, Villeurbanne, France
Copyright Elsevier

The segregation of metallic cores from silicate mantles during early planetary differentiation is a key process shaping the chemical evolution of terrestrial bodies. A critical factor controlling metal-silicate equilibration during this stage is the diffusive behavior of moderately siderophile elements, which governs chemical exchange timescales. As a moderately siderophile and moderately volatile element, Ge is particularly sensitive to redox conditions, pressure, temperature, and the presence of light elements in the metal phase, making it an ideal tracer of core formation processes. However, experimental constraints on Ge diffusion under relevant high-pressure, high-temperature, and low oxygen fugacity conditions are lacking.
Here, we present new experimental measurements of Ge diffusion coefficients in Fe-Ni metal and silicate (CMAS) melt, analogous to planetary cores and mantles, under high-pressure (0.5 – 1 GPa), high-temperature (1350 °C) conditions and low oxygen fugacities (IW − 5.4 to IW − 1.5). Ge diffusion in liquid silicate and liquid metal was found to be significantly faster (∼10−11 m2/s) than in solid metal (∼10−13 m2/s), with transport further influenced by oxygen fugacity and Si content. Under highly reducing conditions, high Si concentrations inhibit Ge diffusion in solid metal by reducing vacancy availability and inducing partial melting, forming immiscible metal droplets that act as localized Ge sinks. Diffusion timescale calculations indicate that, for Earth-like planets, even at high temperatures (1800 °C), estimated equilibration times are too long for large metal fragments (> 10 m) to fully equilibrate before descending to the core. Thus, additional processes such as turbulent convection or percolation are required for efficient metal–silicate exchange. In contrast, on Mars-like bodies with long-lived magma oceans, solely diffusion, even at low temperature (1350 °C), could be sufficient to equilibrate large metal fragments.

¹Addi Bischoff,¹Maximilian P. Reitze,²Julia Roszjar,¹Markus Patzek,^3,4Jean-Alix Barrat,⁵Jasper Berndt,⁶Tommaso Di Rocco,⁶Andreas Pack, Iris Weber
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70072]
¹Institut für Planetologie, University of Münster, Münster, Germany
²Department of Mineralogy and Petrography, Natural History Museum Vienna, Vienna, Austria
³Univ Brest, CNRS, Ifremer, IRD, LEMAR, Institut Universitaire Européen de la Mer (IUEM), Place Nicolas Copernic, Plouzané, France
⁴Institut Universitaire de France, Paris, France
⁵Institut für Mineralogie, University of Münster, Münster, Germany
⁶Universität Göttingen, Geowissenschaftliches Zentrum, Göttingen, Germany
Pubslished by arrangement with John Wiley & Sons

A bright fireball was seen at 4:46 a.m. CET on November 19, 2020, over Austria, and also eye witnessed in Italy and Germany. The resulting Kindberg meteorite was the fifth well-approved meteorite fall in Austria, and all rocks represent ordinary chondrites. One specimen of Kindberg, measuring 233.08 g, was recovered on July 4, 2021, largely covered by a dark brownish fusion crust. The meteorite is an L6 ordinary chondrite (OC) breccia; Kindberg’s highly equilibrated type 6 character is also supported by the large-sized plagioclase grains (An9-12; with grains >100 μm) and the homogeneous compositions of olivine (Fa24.4±0.4) and low-Ca pyroxene (Fs20.6±0.3). The meteorite shows remarkable shock effects in the form of easily visible dark shock veins cross-cutting the bulk rock. The olivine in Kindberg is dominated by grains with undulous extinction or planar fractures, indicating a weakly shocked (S3 [C-S3]) chondritic rock. Close to the shock veins, olivine can also show mosaicism. In addition, wadsleyite, a high-pressure polymorph of olivine, was identified by Raman and IR spectroscopy. Wadsleyite, sometimes in paragenesis with maskelynite and locally part of an intergrowth with majorite and perhaps ringwoodite, was found within and close to the veins. The occurrence of high-pressure phases of olivine and maskelynite in a weakly shocked bulk rock clearly indicates their formation at relatively low equilibrium shock pressures of <20 GPa (S3/S4 transition). Equilibrium shock pressures consistent with those experienced by bulk rocks shocked to S5 (>30–35 GPa) and S6 (>45 GPa; S5/S6 transition) are not required to form high-pressure polymorphs of olivine. The L-chondrite classification is confirmed by O isotope data. The bulk chemical composition also supports L-group membership.