^1,2Bing Yang,¹Jiuxing Xiad,^1,2Xuan Guo,^1,Huaiwei Ni,³Anat Shahar,³Yingwei Fei,³Richard W.Carlson,^1,2Liping Qin
Earth and Planetary Science Letters 595, 117701 Link to Article [https://doi.org/10.1016/j.epsl.2022.117701]
¹CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
²CAS Center for Excellence in Comparative Planetology, China
³Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
⁴Institute of Geology and Geophysics, School of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027, China
Copyright Elsevier

Core formation may modify the stable isotopic signatures for both the mantles and cores of differentiated planetary bodies. We performed high P-T experiments with a piston-cylinder apparatus at 1 GPa and 1873-2073 K to determine the Cr isotopic fractionation factor during metal-silicate segregation. Experimental results consistently indicate that the metal phase is isotopically heavier than the coexisting silicate phase, with Cr_{metal-silicate} up to 0.3‰ at the investigated experimental conditions. Oxygen fugacity, silicate composition, and S content in the metal phase do not have significant effects on the Cr isotopic fractionation factor. By contrast, increasing Ni content in the metal increases the Cr_{metal-silicate} value, implying that the Ni content of the core could influence planetary isotopic signatures. We conclude that heavier Cr isotopes enter the core preferentially during planetary core formation. The Cr value of the terrestrial mantle could be lowered by up to ∼0.02‰ by core formation, despite that this is within current analytical uncertainty of chondritic Cr isotopic composition. For smaller bodies such as the Moon, Mars, and Vesta, the lower core formation temperatures could potentially generate a resolvable core-mantle Cr isotopic fractionation. However, the Moon’s small core size would limit the change in the Cr isotopic composition of the lunar mantle compared to chondritic. For Vesta and Mars, core formation could lower the Cr values of their mantles by ∼0.01-0.02‰, which is trivial relative to the analytical uncertainty. On the other hand, core formation could increase the Cr values of the cores of the parent bodies of iron meteorites by up to ∼0.2‰ at 1873 K. Therefore, the significantly heavy Cr isotopic composition (up to 2.85‰) of iron meteorites cannot be explained by equilibrium fractionation between the core and the mantle of the parent bodies of iron meteorites.

^1,2Jan Render,^1,2Gregory A.Brenneck,¹Christoph Burkhardt,^1,3Thorsten Kleine
Earth and Planetary Science Letters 595, 117748 Link to Article [https://doi.org/10.1016/j.epsl.2022.117748]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, Münster, 48149 Germany
²Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA, USA
³Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
Copyright Elsevier

Nucleosynthetic isotope signatures in meteorites provide key insights into the structure and dynamics of the solar protoplanetary disk and the accretion history of the planets. We present high-precision Zr isotopic data of a comprehensive suite of non-carbonaceous (NC) and carbonaceous (CC) meteorites, and find that various meteorite groups, including enstatite chondrites, exhibit ⁹⁶Zr enrichments, whereas there is no resolved ⁹¹Zr and ⁹²Zr variability. These new Zr isotope data reveal the same fundamental NC-CC dichotomy observed for several other elements, where CC meteorites are more anomalous compared to NC meteorites and are shifted towards the isotopic composition of Ca-Al-rich inclusions (CAIs). For Zr and other elements, the CC composition is reproduced as a mixture of materials with CAI-like and NC-like isotopic compositions in approximately constant proportions, despite these elements exhibiting disparate nucleosynthetic origins or different cosmo- and geochemical behaviors. These constant mixing proportions are inconsistent with an origin of the dichotomy by thermal processing or selective dust-sorting in the disk but indicate mixing of isotopically distinct materials with broadly solar chemical compositions. This corroborates models in which the NC-CC dichotomy reflects time-varied infall from an isotopically heterogeneous molecular cloud. Among NC meteorites, the isotope anomalies in Zr are linearly correlated with those of other elements, which likewise reflects primordial mixing. Lastly, the new Zr isotope data reinforce the notion that Earth incorporated s-process enriched material from the innermost Solar System, which is not represented by known meteorites. By contrast, contributions to Earth and Mars from outer Solar System CC-like materials were limited, indicating that these planets did not form by pebble accretion, which would have led to high CC fractions.

¹A.-M.Seydoux-Guillaume,²T.de Resseguier,³G.Montagnac,⁴S.Reynaud,⁵H.Leroux,³B.Reynard,⁶A.J.Cavosie
Earth and Planetary Science Letters 595, 117727 Link to Article [https://doi.org/10.1016/j.epsl.2022.117727]
¹Univ Lyon, UJM, UCBL, ENSL, CNRS, LGL-TPE, F-42023 Saint Etienne, France
²PPRIME, CNRS-ENSMA-Université de Poitiers, 1 avenue Clément Ader, 86961 Futuroscope, France
³Univ Lyon, ENSL, UCBL, UJM, CNRS, LGL-TPE, F-69007 Lyon, France
⁴Université de Lyon, UJM-Saint-Etienne, CNRS, Institut d’Optique Graduate School, Laboratoire Hubert Curien UMR 5516, F-42023 Saint-Etienne, France
⁵Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et Transformations, F-59000 Lille, France
⁶The Space Science and Technology Centre (SSTC) and the Institute for Geoscience Research (TIGeR), School of Earth and Planetary Science, Curtin University, Perth, WA 6102, Australia
Copyright Elsevier

Impact-related damage in minerals and rocks provides key evidence to identify impact structures, and deformation of U-Th-minerals in target rocks, such as monazite, makes possible precise dating and determination of pressure-temperature conditions for impact events. Here a laser-driven shock experiment using a high-energy laser pulse of ns-order duration was carried out on a natural monazite crystal to compare experimentally produced shock-deformation microstructures with those observed in naturally shocked monazite. Deformation microstructures from regions that may have experienced up to ∼50 GPa and 1000 °C were characterized using Raman spectroscopy and transmission electron microscopy. Experimental results were compared with nanoscale observations of deformation microstructures found in naturally shocked monazite from the Vredefort impact structure (South Africa). Raman-band broadening observed between unshocked and shocked monazite, responsible for a variation of ∼3 cm−1 in the FWHM, is interpreted to result from the competition between shock-induced distortion of the lattice, and post-shock annealing. At nanoscale, three main plastic deformation structures were found in both naturally and experimentally shocked monazite: deformation twins, mosaïcism, and deformation bands. The element Ca is enriched along host-twin boundaries, which further confirms that the laser shock loading experiment produced both comparable styles of crystal-plastic deformation, and also localized element mobility, as that found in natural shock-deformed monazite. Deformation twins form in the experiment were only along the (001) plane, an orientation which is not considered diagnostic of shock deformation. However, both mosaïcism and deformation, expressed in SAED patterns as streaking of spots, and the presence of extra spots (more or less pronounced), are interpreted as unambiguous nano-scale signatures of shock metamorphism in monazite. Experimentally calibrated deformation features, such as those documented here at TEM-scale, provide new tools for identifying evidence of shock deformation in natural samples.

¹Maryjo Brounce,²Jeremy W.Boyce,²Francis M.McCubbin
Earth and Planetary Science Letters 595, 117784 Link to Article [https://doi.org/10.1016/j.epsl.2022.117784]
¹Department of Earth and Planetary Sciences, University of California Riverside, Riverside, CA 92521, USA
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
Copyright Elsevier

Estimates of the oxygen fugacity (fO2) recorded by the Martian nakhlite meteorites from direct observations of the main igneous phenocryst assemblages range from values similar to that recorded by the quartz-fayalite-magnetite oxygen buffer to ∼two orders of magnitude lower. Inferences of changes in fO2 during the late stages of crystallization, volcanic degassing, and emplacement of the nakhlite cumulate pile have been made based on variable sulfide and apatite chemistry. We present S-XANES measurements of the oxidation state of sulfur in apatite and associated mesostasis glass in Nakhla to place direct constraints on the magnitude of changes in fO2 experienced by the Nakhla portion of the nakhlite cumulate pile during apatite crystallization. Nakhla apatites range from containing dominantly S2− to containing dominantly S6+. This, together with correlations between S2−, Cl, and FeO in the mesostasis glass near these apatites, suggest that our measurements capture directly the oxidation of the interstitial late-stage Nakhla magmas as the result of Cl-saturation and degassing. As the result of this degassing, at least part of the nakhlite cumulate pile experienced an increase in fO2 of ∼1.5–2.5 orders of magnitude during apatite crystallization and final mesostasis cooling. Based on these measurements, the sulfur oxidation states of apatites in the other nakhlite meteorites are predicted to range from exclusively S2−-bearing to exclusively S6+-bearing.

^1,2,3J.S.Gorce,^1,2D.W.Mittlefehldt,²J.I.Simon
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.034]
¹Lunar and Planetary Institute, USRA, TX 77058, USA
²Center for Isotope Cosmochemistry and Geochronology, Astromaterials Research Office, NASA/Johnson Space Center, Houston, TX 77058, USA
³Rensselaer Polytechnic Institute, Department of Earth and Environmental Science, Troy, NY 12180
Copyright Elsevier

Eucrites exhibit a range of igneous and metamorphic textures and geochemistries that can be used to study the evolution of early planetary differentiation and crust formation in the solar system. We integrated petrologic/textural observations, in-situ geochemical analyses, and thermodynamic modeling to explore the petrogenesis of Elephant Moraine (EET) 90020, an unbrecciated meteorite. We identified microdomains that record relatively high metamorphic temperatures and concluded that diffusion processes likely modified EET 90020 during and/or after peak thermal conditions. There is little evidence that partial melting caused the distribution of minor and trace elements within or among the microdomains. Trace element linear transect measurements within the microdomains imply that phosphate minerals strongly controlled trace element distributions throughout the sample. The discrepancy between the observed metamorphic textures, major element chemistry, and the trace element distributions is a consequence of differing chemical mobility. Multiple processes are influencing geochemistry within a single sample which has implications for the development of petrogenetic models that seek to reconcile the differences observed between eucrite geochemical groups.

¹Wei Yang et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.030]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Copyright Elsevier

Lunar impact glasses can provide important information on the bulk compositions of their sources and the impact history of the Moon. Here, we report the chemical composition of fifty-four clean glass spherules containing neither relict clasts nor crystals from the Chang’e-5 (CE5) regolith. They can be subdivided into three compositional groups: (1) mid-Ti basaltic (TiO2 = 4.1∼6.5 wt.%), (2) low-Ti basaltic (TiO2 = 1.3∼3.9 wt.%), and (3) high-Al (Al2O3 >15 wt.%). Fifty-one glasses (∼94%) are mid-Ti basaltic, which form a loose compositional cluster for most major and trace elements. These glasses exhibit considerable variations in SiO2 (35.3∼45.3 wt.%). Their TiO2, Al2O3, MgO and CaO show negative correlations with SiO2, while the Na2O, K2O and P2O5 positively correlate with SiO2, also yielding a positive correlation between the CIPW normative plagioclase and olivine. These variations likely result from differential vaporization of SiO2, strongly suggesting an impact origin of these glasses. Their major and trace element compositions are averagely similar to the bulk-rock, in turn indicating that they were formed from the local regolith. The remaining three glasses, including two low-Ti basaltic and one high-Al variety, exhibit distinct major and trace elements from the regolith, indicating an exotic source. In addition, the mid-Ti basaltic glasses provide another approach for estimating the average composition of the CE5 basalt other than directly measuring the small basalt fragments assuming that the exotic materials in the CE5 regolith were limited. This estimation reveals critical trace element characteristics of the CE5 basalt, e.g., it has higher La/Yb (3.71), Sm/Yb (1.76), Sr/Yb (31.6), and (Eu/Eu*)N (0.45) than KREEP, indicating that CE5 basalt must derive from a non-KREEP source. Chemical modeling indicates that the contribution of KREEP-rich materials in the mantle source should be less than 0.3%. The trace element characteristics of the CE5 basalt can be reproduced by extensive (80%) fractional crystallization after low-degree (2%) melting. We propose that this fractional crystallization process might occur at depth, implying vast igneous underplating (7250∼11750 km3) beneath the CE5 landing area. This study also suggests that the high Th concentration (5.43 ppm) is an inherent property of the CE5 basalt resulting from extensive fractional crystallization. Thus, high Th detected by remote sensing may not be associated directly with a KREEP component but rather with highly fractionated basalts.

¹Christophe Drouet,²Matteo Loche,²Sébastien Fabre,²Pierre-Yves Meslin
American Mineralogist 107, 1807-1817 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2022/Abstracts/AM107P1807.pdf]
¹CIRIMAT, Université de Toulouse, CNRS, Toulouse INP, UPS, 4 allée Emile Monso, 31030 Toulouse, France
²Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, UPS, CNRS, CNES, 9 Avenue du Colonel Roche, 31400 Toulouse, France
Copyright: The Mineralogical Society of America

Jahnsites/whiteites are a large family of phosphate hydrate minerals of relevance to terrestrial and
martian mineralogy. It was recently hypothesized as being present in Gale Crater sediments from XRD
analyses performed by the CheMin analyzer aboard the Curiosity rover. However, the conditions of
formation and thermodynamic properties of these compounds are essentially unknown. In this work,
we have optimized the ThermAP predictive thermodynamic approach to the analysis of these phases,
allowing us to estimate for the first time the standard formation enthalpy (ΔHf°), Gibbs free energy
(ΔGf°), and entropy (S°) of 15 jahnsite/whiteite end-member compositions, as well as of related phases
such as segelerite and alluaudites. These estimations were then used to feed speciation/phase diagram
calculation tools to evaluate the relative ease of formation and stability of these hydrated minerals,
including considering present martian conditions. Selected laboratory experiments confirmed calcula-
tion outcomes. All of our data suggest that the formation of jahnsites is an unlikely process, and point
instead to the formation of other simpler phosphate compounds. The stability domain, as calculated
here, also raises serious questions about the possible presence of jahnsites on Mars as in Gale Crater,
which appears rather improbable.

^1,2Niccolò Satta,³Masaaki Miyahara,⁴Shin Ozawa,²Hauke Marquardt,⁵Masahiko Nishijima,⁶Tomoko Arai,⁴Eiji Ohtani
American Mineralogist 107, 1661-1667 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2022/Abstracts/AM107P1661.pdf]

¹Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth 95440, Germany
²Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, U.K.
³Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
⁴Department of Earth Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
⁵Laboratory for Protein Crystallography and Laboratory for Electron Structural Biology Institute for Protein Research, Osaka University, Suita-shi Osaka 565-0871, Japan
⁶Planetary Exploration Research Center, Chiba Institute of Technology, Chiba 275-0016, Japan
Copyright: The Mineralogical Society of America

The Apollo 15 mission returned various samples of regolith breccias, typical lunar rocks lithified
by impact events on the Moon’s surface. Here we report our observations on shock features recorded
in a section of the Apollo Sample 15299. We observe the presence of ferropericlase crystals confined
in a shock-melt pocket and conclude that their formation is related to a shock-induced incongruent
melting of olivine. While predicted by experiments, this phenomenon has never been observed in a
natural sample. The incongruent melting of olivine provides an important signature of melting under
high-pressure conditions and allows for estimating the pressure-temperature (P-T) experienced by the
studied sample during the impact event. We infer that the fracture porosity that likely characterized the
studied sample prior to the shock event critically affected the P-T path during the shock compression
and allowed the studied sample to be subjected to elevated temperature during relatively low shock
pressures.

¹Jens Barosch,¹Larry R. Nittler,¹Jianhua Wang,²Elena Dobrică,³Adrian J. Brearley,⁴Dominik C.Hezel,¹Conel M. O’D. Alexander
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.027]
¹Earth and Planets Laboratory, Carnegie Institution of Washington, 5241 Broad Branch Rd. NW, Washington DC 20015, USA
²Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, 1680 East-West Road, Honolulu 96822, USA
³Department of Earth and Planetary Sciences, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA
⁴Institut für Geowissenschaften, Goethe-Universität Frankfurt, Altenhöferallee 1, 60438, Frankfurt am Main, Germany
Copyright Elsevier

Presolar grains are trace components in chondrite matrices. Their abundances and compositions have been systematically studied in carbonaceous chondrites but rarely in situ in other major chondrite classes. We have conducted a NanoSIMS isotopic search for presolar grains with O- and C-anomalous isotopic compositions in the matrices of the unequilibrated ordinary chondrites Semarkona (LL3.00), Meteorite Hills 00526 (L/LL3.05), and Northwest Africa 8276 (L3.00). The matrices of even the most primitive ordinary chondrites have been aqueously altered and/or thermally metamorphosed, destroying their presolar grain populations to varying extents. In addition to randomly placed isotope maps, we specifically targeted recently reported, relatively pristine Semarkona matrix areas to better explore the original inventory of presolar grains in this meteorite. In all samples, we found a total of 122 O-anomalous grains (silicates + oxides), 79 SiC grains, and 22 C-anomalous carbonaceous grains (organics, graphites). Average matrix-normalized abundances with 1σ uncertainties are ppm O-anomalous grains, ppm SiC grains and ppm carbonaceous grains in Semarkona, ppm (O-anom.), ppm (SiC) and ppm (carb.) in MET 00526 and ppm (O-anom.), ppm (SiC) and ppm (carb.) in NWA 8276. In relatively pristine ordinary chondrites and in primitive carbonaceous and C-ungrouped chondrites, the O and C isotopic composition of presolar grains and their matrix-normalized abundances are similar, despite the likely differences in chondrite-formation time and nebular location. These results suggest a relatively homogenous distribution of presolar dust across major chondrite-forming reservoirs in the solar nebula. Secondary asteroidal processes are mainly responsible for differences in presolar grain abundances between and within chondrites, highlighting the need to identify and target the most pristine chondrite matrices for such studies.

¹Samuel Ebert,²Kazuhide Nagashima,¹Addi Bischoff,³Jasper Berndt,²Alexander N.Krot
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.026]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Germany
²School of Ocean, Earth Science and Technology, Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, USA
³Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Germany
Copyright Elsevier

Understanding the genetic relationship between different chondritic components will help to decipher their origin and dynamical evolution within the protoplanetary disk. Here, we obtain insight into these processes by acquiring O-isotope data from 17 Al-rich chondrules from unequilibrated ordinary chondrites (OCs, petrologic type ≤3.2) and four Al-rich chondrules from the CO3.1 carbonaceous chondrite Dar al Gani (DaG) 083. These particular kinds of chondrules are of special interest, as it is suggested that their precursors may have contained refractory material related to Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs).

The four investigated Al-rich chondrules from the CO3.1 chondrite Dar al Gani 083 consist of olivine, low-Ca pyroxene, Ca pyroxene, and spinel phenocrysts embedded in mostly Na-rich glassy mesostasis. Two chondrules have a homogeneous O-isotopic composition and two are heterogeneous in composition. One chondrule contains relict spinel grains with a Δ17O value of −24.3±1.3‰, indicative of 16O-rich precursor refractory material, similar to constituents of CAIs and AOAs. The presence of CAI-like precursors for the Al-rich chondrules from CO chondrites is consistent with their previously reported presence of 50Ti excesses (Ebert et al., 2018).

The Al-rich chondrules in the ordinary chondrites studied consist of olivine, low-Ca pyroxene, Ca pyroxene, and, occasionally, spinel phenocrysts embedded in mostly Na-rich glassy mesostasis. Hibonite is present in one Al-rich chondrule. The vast majority of these chondrules have heterogeneous O-isotopic compositions: Chondrule glasses are 16O-depleted compared to chondrule phenocrysts; the Δ17O values of the former approach those of aqueously formed fayalite and magnetite grains in type 3 OCs, ∼ +5‰. We infer that the chondrule glasses experienced O-isotope exchange with an aqueous fluid on the OC parent asteroids.

Chondrule phenocrysts, like spinel, olivine, low-Ca pyroxene, and Ca pyroxene, were not affected by this isotope exchange and preserved their initial O-isotope compositions. The phenocrysts within individual chondrules have similar Δ17O, whereas the inter-chondrule Δ17O values range from −4.5 to +1.4‰, i.e., they are in general 16O enriched relative to the majority of ferromagnesian type I and type II porphyritic chondrules in OCs having Δ17O of ∼ +1‰. Because no relict grains were identified in the Al-rich chondrules from ordinary chondrites, the original O-isotopic composition of the refractory precursor material remains unknown.

Additional detailed Na measurements within olivine grains show no major changes in the Na content of the chondrule melt during their crystallization. This implies either that the Na was part of the precursor material or that the Na was enriched in the chondrule melt/glass after crystallization of the olivines.