^1,2Yankun Di,²Qing-Zhu Yin,³François L.H. Tissot,^1,4Yuri Amelin
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Artile [https://doi.org/10.1016/j.gca.2024.06.012]
¹Research School of Earth Sciences, Australian National University, Acton, ACT 2601, Australia
²Department of Earth and Planetary Sciences, University of California Davis, Davis, CA 95616, USA
³The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
⁴Korea Basic Science Institute, Building 202, 162 YeonGu DanJi-ro, Ochang, Cheongwon, Cheongju, Chungbuk 28119, Republic of Korea
Copyright Elsevier

We introduce a new isotope chronological model in which the natural mass-dependent isotopic fractionation effects of the radioactive (“parent”) and radiogenic (“daughter”) elements are systematically and rigorously considered. Using this model, we show that internally-normalized radiogenic isotopic ratios, commonly determined for daughter elements such as Sr, Nd, Cr, Ni, Hf, W, and Os, are dependent on the extent of natural isotopic fractionation of the daughter and parent elements at the time of system closure. This dependence indicates that (1) in two samples derived from the same isotopically homogeneous source at the same time and with identical radiogenic ingrowth over time, the present-day internally-normalized radiogenic isotope ratios would be different if they were initially fractionated to different degrees, and (2) if different internally-normalized radiogenic isotopic ratios are observed for two co-genetic objects, the difference between them would include contributions from both radiogenic ingrowth and natural isotopic fractionation. Consequently, the isochron dating equations employed in traditional chronological studies will yield inaccurate results when significant natural isotopic fractionation are present among the studied samples. Modified isochron equations that can be used to retrieve correct chronological information from isotopically-fractionated samples are presented. These theoretical considerations are applied to the 87Rb–87Sr, 147Sm–143Nd, and 146Sm–142Nd isotope systems of calcium–aluminium-rich inclusions (CAIs), a set of samples that have undergone significant natural Sr, Nd, and Sm isotope fractionation during their formation. The large natural Sr isotope fractionation (up to ca. 5.3 ‰ for 88Sr/86Sr) in fine-grained CAIs can generate analytically well-resolvable biases (>120 ppm) in the internally-normalized 87Sr/86Sr ratios and lead to significant scatters of their 87Rb–87Sr isochron (in conjunction with scatters induced by open-system disturbances). The 87Rb–87Sr systems of coarse-grained CAIs, on the contrary, are essentially not affected by natural Sr isotopic fractionation due to their much subdued fractionation degrees, resulting in a more robust isochron. Similarly, the large natural Nd (up to ca. 4.0 ‰ for 146Nd/144Nd) and Sm (up to ca. 7.1 ‰ for 152Sm/148Sm) isotopic fractionation in fine-grained CAIs can induce significant scatters of the 147Sm–143Nd isochron if the natural fractionation followed the kinetic or power law, and 146Sm–142Nd isochron if the natural fractionation followed the equilibrium, Rayleigh, or power law. This implies that when studying radioactive isotope systems in objects whose daughter and parent elements can undergo significant isotope fractionation in nature, accompanying stable isotope analyses are necessary for accurate chronological interpretations.

¹Le Zhang,¹Cheng-Yuan Wang,²Hai-Yang Xian,¹Jintuan Wang,¹Yan-Qiang Zhang,³Zhian Bao,¹Mang Lin,¹Yi-Gang Xu
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.06.019]
¹State Key Laboratory of Isotope Geochemistry and CAS Centre for Excellence in Deep Earth Science Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
³State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China
Copyright Elsevier

Impact glasses are abundant in the lunar regolith, and Mg isotopes have the potential to trace components from various lunar crustal reservoirs, which have recently been shown to exhibit large Mg isotopic fractionations. However, it remains unclear whether Mg isotopic fractionation occurs during the formation of impact glasses. In this study, we report in situ Mg isotopic and elemental compositional data for agglutinatic glasses returned by the Chang’e 5 mission and obtained using the laser ablation split stream technique. Vesicular textures, Fe–Ni alloys, tiny Fe droplets, and high Ni contents suggest the studied agglutinatic glasses had an impact origin. The agglutinatic glasses exhibit large Mg isotopic fractionation, with δ26Mg values ranging from −1.36 ‰ to −0.01 ‰. The lack of correlations between δ26Mg values, Ni contents, and ratios between volatile and relatively refractory elements (K/La, Rb/Sr, and Ce/Pb) indicate the addition of a meteoritic component and evaporation was not the major process responsible for the measured Mg isotopic variations. In fact, the MgO profiles and correlations between δ26Mg and MgO, Na2O, Sc, Sr, CaO/Al2O3, and δEu reflect Mg isotopic fractionation caused by Mg diffusion from a region with high Mg contents (i.e., more melted pyroxene) to one with lower contents (i.e., more melted plagioclase). Diffusion modeling shows that the duration of diffusion was less than a fraction of a second. Our results indicate that chemical diffusion can produce large Mg isotopic fractionation in impact glasses on a scale of at least tens of microns, and that isotopic fractionation driven by chemical diffusion needs to be considered when the Mg isotopic compositions of impact glasses are used to identify different lunar rock reservoirs.

¹José A. P. M. Devienne,¹Thomas A. Berndt,²Wyn Williams,¹Shichu Chen
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2023JE008268]
¹Department of Geophysics, School of Earth and Space Sciences, Peking University, Beijing, PR China
²School of GeoSciences, The University of Edinburgh, Edinburgh, UK
Published by arrangement with John Wiley & Sons

An increasing amount of evidence suggests that the tetrataenite-bearing cloudy zones (CZ) in iron and stony-iron meteorites can preserve magnetic records of ancient magnetic activity of their parent bodies over solar system timescales. Tetrataenite islands in the CZ are nanometer-sized (<200 nm) crystals that usually form through ordering from precursor taenite islands upon extremely slow cooling through 320°C. Recent micromagnetic models have shown that such precursor taenite islands form highly thermally stable single-domain (SD) or single-vortex states (SV). In this work we employ a 3D finite element multi-phase micromagnetic modeling to show that tetrataenite inherits the magnetic remanence of taenite precursor when it forms over underlying SD states. When taenite forms SV states, however, tetrataenite resets the precursor magnetization and records a new remanence through chemical ordering at 320°C. We further assess the thermal stability of tetrataenite islands. We show that in cases where tetrataenite inherits the domain states of its precursor taenite, the origin of the remanence can be up to ∼105 years older than previously thought in fast-cooled meteorites, and ∼1–≳6 Myr in slowly cooled meteorites. It indicates, therefore, that different regions across slowly cooled CZ record distinct stages of planetary formation.

¹E. Caminiti,²C. Lantz,³S. Besse,²R. Brunetto,⁴C. Carli,⁵L. Serrano,⁶N. Mari,²M. Vincendon,¹A. Doressoundiram
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116191]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de paris, 5 place Jules Janssen, 92195 Meudon, France
²Institut d’Astrophysique Spatiale, Université Paris- Saclay, CNRS, 91400 Orsay, France
³European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, Villanueva de la Cañada, 28692 Madrid, Spain
⁴IAPS-INAF, Via Fosso del Cavaliere, 100, 00133 Rome, Italy
⁵Independent researcher, 660001 Pereira, Colombia
⁶Department of Earth and Environmental Sciences, University of Pavia, 27100 Pavia, Italy
Copyright Elsevier

The surface of Mercury is subject to space weathering that complicates remote sensing data analysis. We present an experimental study performed on Mercury volcanic surface analogues to provide a better constraint on spectral alterations induced by solar wind. We used 20 keV He+ with fluences up to 5 × 1017 ions/cm2 to simulate ion irradiation reaching the surface. Terrestrial ultramafic lava already identified as good analogues for Mercury were used: a boninite, a basaltic komatiite and a komatiite. Spectra were acquired in the visible to mid-infrared (VMIR) wavelength range, between 0.4 and 16 μm. Spectral alterations induced by irradiation are observed. In the visible to near-infrared (VNIR) samples show an exponential darkening, a reddening and a flattening of spectra. Above a certain irradiation dose (1 × 1017 ions/cm2 in our conditions), the darkening reaches a plateau while the reddening and flattening do not show any definable trend. In the mid-infrared (MIR) we observe a shift of Reststrahlen bands towards longer wavelengths (≤0.42 μm). The Christiansen feature is shifted towards longer or shorter wavelengths according to the irradiation dose (≤0.2 μm). The spectral alteration is closely influenced by the composition. As Mercury’s surface is compositionally heterogeneous, the degree of spectral alteration varies on the planet and putatively participates in the heterogeneous spectral properties of the surface. This work provides ground-truth data for future ESA-JAXA-BepiColombo observations. The alteration of VMIR spectral features induced by ion irradiation simulated in the laboratory will be used for future SIMBIO-SYS (Spectrometer and Imaging for MPO BepiColombo Integrated Observatory SYStem) and MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) data analysis.

^1,2,3Yingnan Zhang,^1,2,3Liping Qin
Earth and Planetary Science Letters 641, 118807 Link to Article [https://doi.org/10.1016/j.epsl.2024.118807]
¹CAS Key Laboratory of Crust-Mantle Materials and Environments, University of Science and Technology of China, Hefei 230026, China
²Deep Space Exploration Laboratory, Hefei 230088, China
³CAS Center for Excellence in Comparative Planetology, Hefei 230026, China
Copyright Elsevier

Thermal metamorphism for asteroids influences their structures and chemical compositions. As the only CCs with the petrologic type of 3-6, their metamorphis history and heat sources are unclear. The isotopic composition of molybdenum (Mo) was used as an indicator of oxidation state to investigate the oxidation and thermal metamorphic history of CK chondrites. CK chondrites are characterized by positively fractionated Mo isotopic composition relative to other chondritic groups, and the degree of enrichment in heavy Mo isotopes in CKs generally decreases with Mo content. Combined with numerical simulations for hexavalent Mo evaporation at elevated temperatures and thermodynamic calculations of the valence transformation of Mo, the Mo isotopic characteristic of CKs is proven in concordance with oxidative Mo lost during thermal metamorphism. This evaporation loss highlights the importance of the parent body process on the MVE depletion. Our results also require oxidation of CKs and subsequent thermal metamorphism to have occurred after the disintegration of the CK parent body. A viable heat source in this scenario could be solar radiation, and the oxidization may perform by the water accretion in orbits.

¹Birgit Schulz,¹Christian Vollmer,^2,3Jan Leitner,⁴Lindsay P. Keller,^5,6Quentin M. Ramasse
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.06.013]
¹Institut für Mineralogie, Universität Münster, Corrensstr. 24, 48149 Münster, Germany
²Institut für Geowissenschaften, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany
³Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
⁴XI3, Astromaterials Research and Exploration Science (ARES) Division, NASA Johnson Space Center, Houston, TX 77058, United States
⁵SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK
⁶School of Chemical and Process Engineering, School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
Copyright Elsevier

GEMS (glass with embedded metal and sulfides) are the dominant carrier of amorphous silicates in anhydrous interplanetary dust particles (IDPs) and one of the most suitable materials to study early solar system processes. Amorphous silicates in 105 GEMS from eight IDPs were analyzed regarding texture and chemical composition to reassess GEMS formation theories and genetic relationships to amorphous silicate material in meteorites. Petrography of bulk IDPs was investigated to understand GEMS’ relationships to other IDP components. Furthermore, carbon and nitrogen isotopic compositions were measured. Nearly all GEMS are aggregates of several subgrains with variable amount of nanophase inclusions and different Mg- and Si-contents, while single GEMS are rare. The subgrains within aggregates are typically surrounded by one or more carbon rims with high density. The chemical compositions of GEMS amorphous silicates are subsolar for all major element/Si ratios but exhibit wide heterogeneity. This is not influenced by silicon oil from the capturing process of IDPs as assumed before, as a penetration of the silicon oil is excluded by high resolution EELS (electron energy loss spectroscopy) areal density maps of silicon. Furthermore, low Fe-content in GEMS amorphous silicates shows that these are not altered by aqueous activity on the parent body as it is the case for amorphous silicate material in primitive meteorites. The subsolar element/Si ratios and the wide chemical heterogeneity point to a non-equilibrium fractional condensation origin either in the early solar nebula or in a circumstellar environment and are not in agreement with homogenization via sputtering in the ISM. The close association with carbon around GEMS subgrains and as double-rims around GEMS aggregates argue for a multi-step aggregation after formation of the smallest GEMS subgrains in the ISM or the early solar nebula. Carbon acting as matrix material connecting GEMS and other IDP components has lower areal density as seen from carbon EELS areal density maps and isotopic anomalies varying at the nanometer scale, pointing to different origins and processing of materials to varying extent or at changing temperatures.

To balance GEMS’ subsolar element/Si ratios, a supersolar component in IDPs was assumed to account for the overall chondritic composition of bulk IDPs. Nevertheless, our bulk IDP analyses revealed subsolar, but variable, element/Si ratios for complete particles as well, depending on type and amount of mineral phases in each particle. Pyroxenes in the investigated particles can occur as elongated euhedral crystals, but are overall rare. The dominant crystalline fraction in the investigated IDP samples are equilibrated aggregates (EAs) that show the same chemical compositions as GEMS, indicating that the EAs are recrystallized GEMS grains and formed after GEMS formation as secondary phases.

^1,2T. J. Barrett,^1,3A. J. King,¹G. Degli-Alessandrini,⁴S. J. Hammond,³E. Humphreys-Williams,³B. Schmidt,¹R. C. Greenwood,¹F. A. J. Abernethy,^1,3M. Anand,⁵E. Rudnickaitė
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14229]
¹School of Physical Sciences, The Open University, Milton Keynes, UK
²Center for Lunar Science and Exploration, Lunar and Planetary Institute, Houston, Texas, USA
³Planetary Materials Group, Natural History Museum, London, UK
⁴School of Environment, Earth, and Ecosystem Sciences, The Open University, Milton Keynes, UK
⁵Department of Geology and Mineralogy, Museum of Geology of Vilnius University, Vilnius, Lithuania
Published by arrangement with John Wiley & Sons

The Padvarninkai meteorite is a relatively understudied eucrite, initially misclassified as a shergottite given its strong shock characteristics. In this study, a comprehensive examination of the petrology; mineral composition; major, minor, and trace element abundances; and isotopic composition (C, O) is presented. Padvarninkai is a monomict eucrite consisting of a fine to coarse-grained lithology and impact melt veins. Pyroxene grains are typically severely fractured and mosaicked whilst plagioclase is either partially or totally converted to maskelynite. Based on shock features observed in pyroxene, plagioclase, and apatite, Padvarninkai can be given a shock classification of M-S4/5. Despite the high shock experienced by this sample, some of the original igneous textures remain. Compositionally, Padvarninkai is a main group eucrite with a flat REE pattern (~10–12 × CI) and elevated Ni abundances. Whilst both new and literature oxygen isotopes are similar to other eucrites, however, Padvarninkai displays an anomalously high δ13C value. To reconcile the high Ni and δ13C value, impact contamination modeling was conducted. These models could not reconcile both the high Ni and δ13C value with the eucritic δ18O values, arguing against impact as a source for these anomalies.

¹Bidong Zhang,²Nancy L. Chabot,¹Alan E. Rubin
Proceedings of the National Academy of Sciences of the United States of America (PNAS) 121, e2306995121 Link to Article [https://doi.org/10.1073/pnas.23069951]
¹Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095-1567
²Space Exploration Sector, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723

Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System, and they preserve information about conditions and planet-forming processes in the solar nebula. In this study, we include comprehensive elemental compositions and fractional-crystallization modeling for iron meteorites from the cores of five differentiated asteroids from the inner Solar System. Together with previous results of metallic cores from the outer Solar System, we conclude that asteroidal cores from the outer Solar System have smaller sizes, elevated siderophile-element abundances, and simpler crystallization processes than those from the inner Solar System. These differences are related to the formation locations of the parent asteroids because the solar protoplanetary disk varied in redox conditions, elemental distributions, and dynamics at different heliocentric distances. Using highly siderophile-element data from iron meteorites, we reconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across the protoplanetary disk within the first million years of Solar-System history. CAIs, the first solids to condense in the Solar System, formed close to the Sun. They were, however, concentrated within the outer disk and depleted within the inner disk. Future models of the structure and evolution of the protoplanetary disk should account for this distribution pattern of CAIs.

^1,2Flore Van Maldeghem et al. (>10)
Earth and Planetary Science Letters 641, 118837 Link to Article [https://doi.org/10.1016/j.epsl.2024.118837]
¹Archaeology, Environmental changes, and Geo-chemistry (AMGC), Vrije Universiteit Brussel, Pleinlaan 2, Brussels B-1050, Belgium
²Center for Star and Planet Formation, Globe Institute, University of Copenhagen, Oester Voldgade 5, 1350 Copenhagen K, Denmark
Copyright Elsevier

Each year, approximately 5000 tons of extraterrestrial material reaches the Earth’s surface as micrometeorites, cosmic dust particles ranging from 10 to 2000 μm in size. These micrometeorites, collected from diverse environments, mainly deep-sea sediments, Antarctic ice, snow and loose sediments, and hot deserts, are crucial in understanding our Solar System’s evolution. Chrome-rich spinel (Cr-spinel) minerals have gained attention as proxies for studying the extraterrestrial flux in sedimentary deposits, because these robust minerals occur, in various extraterrestrial materials, with compositions characteristic of their parent bodies. A total of 27 Cr-spinel bearing micrometeorites within the size range of 185–800 μm, were identified from approximately 6000 micrometeorites from the Transantarctic Mountains (n = 23) and the Sør Rondane Mountains (n = 4), in Antarctica, containing Cr-spinel (8–120 μm), were examined in this study for geochemical composition and high-precision oxygen isotope ratios to assess alteration and identify potential parent bodies.

Oxygen isotopes in the micrometeorite groundmass and in Cr-spinel grains reveal a predominance of ordinary chondritic precursors, with only 1 in 10 micrometeorites containing Cr-spinel minerals showing a carbonaceous chondritic signature. This may be further confirmed by an elevated Al content (> 12 wt% Al₂O₃) in Cr-spinel from specific carbonaceous chondrite types, but a more extensive dataset is required to establish definitive criteria. The first Cr-spinel bearing particle, in an Antarctic micrometeorite, that can be linked to R-chondrites based on oxygen isotopes, has been documented, demonstrating the potential for R-chondrites as a source of chrome-rich spinels. The study also highlights the potential for chemical modifications and alteration processes that Cr-spinel minerals may undergo during their time on the parent body, atmospheric entry, and terrestrial residence.

In the context of the broader micrometeorite flux, the results align with previous findings, showing a consistent contribution of micrometeorites containing Cr-spinel minerals related to ordinary chondrites over the past 2 to 4 million years. This is however a small fraction (∼ 1 %) of the total micrometeorite flux. The study further confirms that Cr-spinel minerals recovered from sedimentary deposits serve as valuable proxies for tracking events related to ordinary chondritic or achondritic materials. However, it is emphasized that Cr-spinel minerals alone cannot serve as exclusive indicators of the overall extraterrestrial flux, especially during periods dominated by carbonaceous chondritic dust in the inner Solar System. To comprehensively understand the complete extraterrestrial flux, additional proxies are needed to trace dust-producing events associated with various Solar System objects. The intricate nature of Cr-spinel compositions, and the potential for alteration processes emphasize the need for further research to refine our understanding of these extraterrestrial markers.

¹Helen Grant,¹Romain Tartèse,¹Rhian Jones,²Laurette Piani,²Yves Marrocchi
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.06.005]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester M13 9PL, UK
²CRPG, CNRS-Université de Lorraine, UMR 7358, Vandoeuvre les Nancy, France
Copyright Elsevier

Deuterium to hydrogen isotope ratios in unequilibrated ordinary chondrites (UOCs) which have undergone little-to-no thermal metamorphism pose an interesting problem when looking at water in the early Solar System. Bulk chondrite studies have shown that UOCs of the lowest subtypes have D/H ratios as high as comets from the outer Solar System, which, along with bulk UOC water abundances, decrease with thermal metamorphism. Since bulk UOC analyses represent a complex mixture of organic and hydrated phases, it is not clear what phase(s) is responsible for the high bulk D/H values. In this study, we report in situ secondary ion mass spectrometry (SIMS) measurements of the H isotope composition of the fine-grained matrix of UOCs with petrological subtypes ranging from 3.00 to 3.9. We find that for matrix areas in UOCs of petrologic subtype ≥3.2, correlations between D-rich organic material and D-poor phyllosilicates give relatively D-poor intrinsic water isotopic compositions, with δD values between −320 ± 91 ‰ and −71 ± 71 ‰, which are inherited from parent body accretion. Therefore, we conclude that OC parent bodies accreted D-poor water ice that had an H isotopic composition similar to that of CM and CV chondrite parent bodies. We find that matrix in UOCs of the lowest subtypes (Semarkona, Bishunpur, and Ngawi) show similar water and organic H isotope compositions to higher type UOCs. Our in situ analyses also show that matrix areas in these pristine UOCs contain a third, thus far unidentified, component that carries the high D/H signature, with δD values up to ∼6000 ‰. We propose that this component is pristine amorphous silicates preserved from the molecular cloud or early protoplanetary disc that is extremely sensitive to thermal and aqueous alteration on asteroidal parent bodies.