 | Isotopic fractionation of neon during magma degassing Abstract: Determining the neon isotope composition of the Earth’s mantle is key to unravelling how light noble gases became part of the primordial Earth. However, accurately measuring neon abundance and isotopic composition in primary mantle melts is challenging due to the low concentration of neon, coupled with potential isotopic fractionation during transport and degassing. Interestingly, natural samples that exhibit solar-like neon isotopic compositions, ranging between the values calculated for the Sun (20Ne/22Ne = 13.36 ± 0.09; Heber et al., 2012) and those resulting from solar wind implantation and sputtering (20Ne/22Ne = 12.73; Moreira and Charnoz, 2016), support the idea that the Earth’s mantle might have trapped a primordial nebula in its early formation stages. Analyses of three synthetic vesiculated glasses, produced at ∼1.7 kbar and 1200 °C using a starting material with an air-like isotopic composition (20Ne/22Ne = 9.81 and 21Ne/22Ne = 0.0287) fluxed with CO2, reveal significant isotopic fractionation of Ne within trapped vesicles. Measured values reach 20Ne/22Ne = 10.50 ± 0.14. The isotopic variations among individual vesicles align with expectations for kinetic fractionation, suggesting that degassing processes affect Ne isotope composition of basaltic melts. |
 | Earth’s deep magma ocean never reached sulfide saturation Abstract: The chondritic abundances of highly siderophile elements in the Earth’s mantle have been proposed to result from the combination of pervasive exsolution and segregation of sulfide from the magma ocean, along with late accretion. Therefore, evaluating the sulfur storage capacity (i.e. sulfur solubility) of the deep magma ocean is key to understanding the late stages of Earth’s formation. Here, we have investigated the effects of high pressure and high temperature on the solubility of sulfur in the deep primordial magma ocean by melting and equilibrating a pyrolytic glass with pure FeS in a laser-heated diamond anvil cell. Chemical analysis of the run products show that significant amounts of sulfur can be stored deep in the magma ocean (∼1 wt. %). We developed a thermodynamic parameterisation predicting the solubility of sulfur at sulfide saturation (SCSS) depending on pressure, temperature and silicate composition. We show that SCSS always exceeds the amount of sulfur present in the mantle due to metal-silicate partitioning, consistent with previous work. Consequently, it appears that Earth’s magma ocean likely never reached sulfur saturation, thereby preventing the segregation of a sulfide-rich melt, also referred as the “Hadean matte”. |
 | Serpentinite dehydration in the subducted lithosphere produces no B isotopic fractionation Abstract: The fate of boron (B) and its isotopes during serpentinite dehydration is a matter of debate. To contribute to a better understanding of the B isotopic fractionation upon serpentinite dehydration, we present in situ δ11B analyses of antigorite and olivine from subducted high pressure serpentinites from the Western Alps (Zermatt-Saas and Erro-Tobbio). The different isotopic compositions of antigorite in different parts of the units (δ11B of −5 to +10 ‰ and +13 to +19 ‰ for Zermatt-Saas, and δ11B of up to +26 ‰ for Erro-Tobbio) are inherited from variable serpentinisation conditions on the sea floor. Serpentinite dehydration via the brucite-out reaction during subduction produces metamorphic olivine in oxygen (O) isotopic equilibrium with antigorite. This olivine shows near zero B isotopic fractionation with coexisting antigorite (Δ11BOl-Atg of −0.7 ± 3.4 ‰), which implies little B isotopic fractionation during serpentinite dehydration. In contrast, significant B isotopic disequilibrium (Δ11BOl-Atg of +25 ‰) is found between antigorite and olivine formed in shear bands, shear zones and veins, indicating influx of channelled external fluids, including serpentinite-derived fluids from a protolith with a different isotopic composition. |
 | Control of organic matter on metal mineralisation in uranium-rich black shale “Kupferschiefer” Abstract: The natural formation of economically important metal sulfides in the geological “Kupferschiefer” system in Central Europe (i.e. its mineralisation) results from a complex and poorly understood interplay of various processes involving organic matter (OM). Here, we demonstrate that transport of aqueous fluids rich in metal chlorides was limited by laminated, non-porous, and non-fluorescent solid OM in the TOC- and uranium-rich shale T1 of the Kupferschiefer system. These organic laminae exhibit XANES spectra consistent with irradiated type I kerogen or pyrobitumen and can thus be interpreted as remains of fossilised algal mats. The laminae not only enhanced sealing integrity against metal-rich aqueous fluids, but also acted as reductant for metal chloride. Moreover, retained paraffinic oil clogged pore space and reduced permeability. Similar to processes in petroleum systems, metal-rich chloride brines migrated into a shale reservoir with calcite porosity which was self sealed by internal, impermeable organic laminae. Our results highlight that the fate and behaviour of OM and its degradation products are key for the understanding of a variety of organic-inorganic interactions as they bridge the gap between different geochemical sinks. |
 | Corrigendum to “Young oxygenation of the Archean Keonjhar Palaeosol, India, from 138La-138Ce chronometry” by Pfennig et al., 2025 |
 | Ageing of organic materials at the surface of Mars: A Raman study aboard Perseverance Abstract: The Perseverance rover is exploring Jezero crater on Mars, one of its goals being to collect samples to be returned to Earth to search for organic remains of ancient Martian life. However, the organic content of these rocks has likely suffered from the radiation environment on the surface of Mars to an extent yet to be quantified. For the first time, a 1000 sols long ageing experiment was conducted at the surface of Mars, i.e. under actual Martian conditions, relying on the 100 % organic Ertalyte target carried by Perseverance. White at landing, the Ertalyte target has turned brown with time, while its Raman signal changed, with a modification of the background (its maximum has shifted from 1500 to 2000 cm−1) and a reduction of the contribution of the Raman signal of Ertalyte (by a factor of 5 over the first 500 sols). Given the intrinsic resistance of the Ertalyte to UV exposure, which is not anticipated for most Martian organic materials, these results suggest that exposure at the surface of Mars will make the detection of Martian organic molecules challenging. |
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