¹Laura B. Seifert,¹Pierre Haenecour,^1,2Thomas J. Zega
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13811]
¹Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson, Arizona, 85721 USA
²Department of Materials Science and Engineering, University of Arizona, 1235 E. James E. Rogers Way, Tucson, Arizona, 85721 USA
Published ba arrangement with John Wiley & Sons

We report the structural and chemical analyses of six presolar silicate grains identified in situ in the CO3.0 carbonaceous chondrite Dominion Range (DOM) 08006. Two of the grains have O-isotopic compositions consistent with origins in the circumstellar envelopes of low-mass (<2M☉) asymptotic giant branch (AGB)/red giant branch (RGB) stars, although without Mg-isotopic data, origins in supernovae (SNe) cannot be ruled out. The other four grains have O-isotopic compositions consistent with origins in the ejecta of type-II SNe. Transmission electron microscopy analyses reveal that all grains are crystalline (single crystal or polycrystalline) and have varied compositions. The analyzed AGB/RGB grains include an Fe-rich crystalline olivine with an Fe-sulfide inclusion and a chemically zoned olivine grain that also contains an Fe-oxide rim. The grains derived from SNe include two polycrystalline assemblages with structures that overlap with both olivine and pyroxene, an assemblage composed of both a single crystal of forsterite and polycrystalline forsterite, and an orthopyroxene grain with an embedded Fe-sulfide crystal. The thermodynamic origins of both AGB/RGB and SN grains are also diverse. The structure and compositions of two grains are consistent with equilibrium thermodynamic predictions of condensation, whereas four are not, suggesting formation through nonequilibrium or multistep processes. Our observations of presolar silicate grains suggest that the circumstellar envelopes of AGB/RGB stars and the ejecta of SNe can produce grains with comparable structures and compositions.

¹Nicolas P. Walte,²Gregor J. Golabek
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13810]
¹Heinz Maier-Leibnitz Center for Neutron Science (MLZ), Technical University Munich, Garching, 85748 Germany
²Bayerisches Geoinstitut (BGI), University of Bayreuth, Bayreuth, 95447 Germany
Published by arrangement with John Wiley & Sons

Olivine aggregates, bodies found in pallasites that consist of olivines with coherent grain boundaries and minor amounts of Fe-Ni and troilite, likely represent well-preserved samples of different mantle regions of pallasite parent bodies (PPBs). We investigated olivine aggregates from the main group pallasites Fukang, Esquel, Imilac, and Seymchan and compare their textures with results from deformation experiments. Our measurements reveal an inverse relationship between the grain size of olivines and the primary metal fraction inside olivine aggregates, which is explained by simultaneous grain growth retarded by Zener pinning in different mantle regions. Textural evidence indicates that the mantle has remained at high temperatures before initial cooling occurred shortly after pallasite formation that was likely caused by an impact. Different degrees of annealing of the deformation textures suggest that the postcollisional cooling occurred in the order Seymchan, Imilac, Esquel, and Fukang. We interpret this observation with an increasing burial depth after the collision. We also demonstrate that the mantle has not been convecting before the impact despite being at high temperature. Using the minimum critical Rayleigh number, we estimate PPB radii assuming different core radii. Our results question the recent ferromagmatism hypothesis for pallasite formation and support a multistage formation process that includes one or several impacts.

¹Michael Zolensky et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13808]
¹Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

Our goal was to devise a bridge between shock determinations of asteroid regolith grains by standard light optical petrography, synchrotron X-ray diffraction (SXRD), and electron backscattered diffraction (EBSD). We determined the optimal conditions under which to measure the shock stage of olivine crystals in astromaterial grains by EBSD. We applied this EBSD procedure to the shock stage determination of four regolith grains from asteroid Itokawa, returned to earth by the Hayabusa spacecraft. Interpretation of these data required a parallel examination of three ordinary chondrite standards that exhibited shock histories ranging from stage 2 to stage 4, using all three techniques. Standard light optical petrography indicated shock stage of S2/3 for the 24 Itokawa grains analyzed. SXRD results for seven Itokawa grains indicate a shock stage of S2. EBSD maps of four Itokawa grains indicate shock stage S3. Thus, the different techniques indicate slightly different shock stages, probably due to small sampling populations for EBSD and SXRD. We therefore recommend that significantly more than seven regolith grains should be separately analyzed by any shock determination technique, probably between 10 and 20. In any case, Itokawa regolith grains have been shocked to stage S2/3, or approximately 5–10 GPa. Finally, we investigated the crystallinity of one Itokawa olivine by SXRD, determining that the 5–10 GPa shock it had experienced did not appreciably alter the size of the unit cell, contrary to some previous suggestions.

¹Christopher K. Junium,²Aubrey L. Zerkle,³James D. Witts,¹Linda C. Ivany,⁴Thomas E. Yancey,⁵Chengjie Liu,²Mark W. Claire
Proceedings of the National Academy of Science of the USA (PNAS) 119 (14) e2119194119 Link to Article [https://doi.org/10.1073/pnas.2119194119]
¹Department of Earth and Environmental Sciences, Syracuse University, Syracuse, NY13244
²School of Earth and Environmental Sciences,Centre for Exoplanet Science, University of St Andrews, StAndrews KY16 9AL, United Kingdom
³School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom
⁴The College of Geosciences, Texas A&MUniversity, College Station, TX 77483
⁵Ellington Geological Services, Houston, TX 77043

Sulfate aerosols have long been implicated as a primary forcing agent of climate change and mass extinction in the aftermath of the end-Cretaceous Chicxulub bolide impact. However, uncertainty remains regarding the quantity, residence time, and degree to which impact-derived sulfur transited the stratosphere, where its climatic impact would have been maximized. Here, we present evidence of mass-independent fractionation of sulfur isotopes (S-MIF) preserved in Chicxulub impact ejecta materials deposited in a marine environment in the Gulf Coastal Plain of North America. The mass anomalous sulfur is present in Cretaceous–Paleogene event deposits but also extends into Early Paleogene sediments. These measurements cannot be explained by mass conservation effects or thermochemical sulfate reduction and therefore require sulfur-bearing gases in an atmosphere substantially different from the modern. Our data cannot discriminate between potential source reaction(s) that produced the S-MIF, but stratospheric photolysis of SO₂ derived from the target rock or carbonyl sulfide produced by biomass burning are the most parsimonious explanations. Given that the ultimate fate of both of these gases is oxidation to sulfate aerosols, our data provide direct evidence for a long hypothesized primary role for sulfate aerosols in the postimpact winter and global mass extinction.

^1,2Valerie Payre,¹Rajdeep Dasgupta
Geochimica et Cosmochimica acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.03.034]
¹Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, Texas 77005
²Present address: Department of Physics and Planetary Sciences, Northern Arizona University, Flagstaff, Arizona
Copyright Elsevier

Phosphorus is estimated to be ten times more enriched in the martian mantle compared to the terrestrial mantle. Yet, its effects on primary melt composition and melting phase relations in martian systems is unknown. We performed piston-cylinder experiments at a constant upper mantle pressure of 2 GPa and temperatures of 1210-1450 °C using a model martian primitive mantle composition with P2O5 content of 0 and 0.5 wt.%. All experiments produced an assemblage of olivine + orthopyroxene + melt ± pigeonite ± apatite ± spinel. Our experimental results, in combination with a previous study at similar P-T conditions and major element bulk composition but containing 0.2 wt.% bulk P2O5, show that the addition of phosphorus dramatically increases the abundance of more polymerized residual mineral such as orthopyroxene while decreasing the proportion of less polymerized residual phases such as olivine, especially at low extent of melting (∼11 wt.%). Such effects lead to lower SiO2 concentrations in the near-solidus melt by up to 10 wt.% for mantle P2O5 of 0.2 and 0.5 wt.%. Increasing bulk P2O5 to 0.5 wt.% also leads to elevated CaO/Al2O3 ratio and increased FeO* concentration in mantle-derived melts with the latter likely due to formation of Fe-O-P complexes in the liquid. Our study suggests that elevated phosphorus in the martian mantle has important consequences regarding the composition and mineralogy of the crust, partly made with primary melts, and of the upper mantle. Because of elevated P, variably melt-depleted upper mantle of Mars is likely to be richer in orthopyroxene compared to the terrestrial mantle and the elevated P content is partly responsible for several geochemical attributes of martian basalts compared to those on Earth. Extrapolating our experimental results to a range of pressures, we suggest a depletion of P in the mantle through time, which likely contributed to major elemental compositional differences between ancient Gusev and Gale crater basalts and more recent martian meteorites.

¹Chennaoui Aoudjehane H.
Advances in Science, Technology and Innovation 978, 345 – 348 Link to Article [DOI 10.1007/978-3-030-72547-1_74]
¹GAIA Laboratory, Faculty of Sciences Ain Chock, Hassan II University of Casablanca, km8 Route d’El Jadida, 20150, Casablanca, Morocco

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¹Rappenglück M.A.
Minerals 12, 188 Open Access Link to Article [DOI 10.3390/min12020188]
¹Adult College and Observatory Gilching, Gilching, 82205, Germany

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¹Cox M.A.,¹Cavosie A.J.,¹Orr K.J.,²Daly L.,³Martin L.,¹Lagain A.,^1,4Benedix G.K.,¹Bland P.A.
Science Advances 8, eabl7497 Open Access Link to Article [DOI 10.1126/sciadv.abl7497]
¹Space Science and Technology Centre (SSTC), School of Earth and Planetary Science, Curtin University, Perth, 6102, WA, Australia
²School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
³Centre for Microscopy, Characterisation and Analysis (CMCA), The University of Western Australia, 6 Verdun Street, Perth, 6009, WA, Australia
⁴Department of Earth and Planetary Sciences, Western Australia Museum, WA, Australia

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¹Nicolas Schnuriger,¹Camille Cartier,¹Johan Villeneuve,²Valentina Batanova,¹Maxence Regnault,¹Yves Marrocchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13802]
¹Université de Lorraine, CRPG, CNRS, UMR 7358, Vandœuvre-lès-Nancy, 54501 France
²Université Grenoble Alpes, ISTerre, CNRS, UMR 5275, Grenoble, 38000 France
Published by arrangement with John Wiley & Sons

In carbonaceous chondrites, Mg-spinel (MgAl2O4) grains are ubiquitous in refractory inclusions but rarely reported in chondrules, where they may correspond to minerals either (i) inherited from chondrule precursors or (ii) crystallized from chondrule melts. Here, we report high-current quantitative electron microprobe measurements and secondary ion mass spectrometry oxygen isotopic analyses of Mg-spinel-bearing chondrules in the CV3 carbonaceous chondrites Northwest Africa 10235 and Allende. Compared to spinels in refractory inclusions, chondrule spinels are characterized by higher Cr contents and 16O-poorer oxygen isotopic signatures (∆17O ≡ δ17O−0.52 × δ18O, from −2 to −6‰). Because the similar Δ17O values of chondrule olivine and spinel crystals imply their comagmatic origin, we applied a geothermometer based on the Al-Cr distribution between these minerals to determine their crystallization temperatures. The calculated temperatures range from 1200 to 1640 °C (mean = 1470 °C), most being lower than the estimated liquidus temperature of porphyritic chondrules (~1600 °C). Our results suggest that chondrules experienced relatively slow cooling rates (slower than a few hundreds of °C h−1), which is in good agreement with models of chondrule formation invoking nonlinear or two-stage cooling rates.

¹J.Eschrig,¹L.Bonal,²M.Mahlke,²B.Carry,¹P.Beck,³J.Gattacceca
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115012]
¹Institut de Planétologie et d’Astrophysique de Grenoble, Université Grenoble Alpes, CNRS CNES, 38000 Grenoble, France
²Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
³CNRS, Aix Marseille Univ, IRD, Coll France, CEREGE, Aix-en-Provence, France
Copyright Elsevier

The search for asteroidal parent bodies of chondrites through various techniques is an ongoing endeavor. A link between ordinary chondrites (OCs) and S-type asteroids has previously been established by the sample return of the Hayabusa space mission. OCs are the class with the most abundant samples in our meteorite collection. We present an in-depth study of the reflectance spectra of 39 equilibrated and 41 unequilibrated ordinary chondrites (EOCs and UOCs). We demonstrate that consistent measuring conditions are vital for the direct comparison of spectral features between chondrites, otherwise hampering any conclusions. We include a comparison with a total of 466 S-type asteroid reflectance spectra from various databases. We analyze (i) if a difference between EOCs and UOCs as well as between H, L and LL can be seen, (ii) if it is possible to identify unequilibrated and equilibrated S-type asteroid surfaces and (iii) if we can further constrain the match between OCs and S-type asteroids all based on reflectance spectra.

As a first step, we checked the classification of the 31 Antarctic UOCs analyzed in the present work, using petrography and magnetic measurements, and evidenced that 74% of them were misclassified. Reflectance spectra were compared between EOCs and UOCs as well as between H, L and LL chondrites using a set of spectral features including band depths and positions, peak reflectance values, spectral slopes and the Ol/(Ol + Px) ratio. UOCs and EOCs reflectance spectra show no clear-cut dichotomy, but a continuum with some EOCs showing stronger absorption bands and peak reflectance values, while others are comparable to UOCs. Moreover, we show by the example of 6 EOCs that their band depths decrease with decreasing grain size. Based on reflectance spectra alone, it is thus highly challenging to objectively identify an unequilibrated from an equilibrated S-type surface. There is no clear distinction of the chemical groups: only LL EOCs of petrographic type >4 can be distinguished from H and L through less deep 2000 nm band depths and 1000 nm band positions at longer wavelengths. No dichotomy of S-type asteroids can be seen based on the Ol/(Ol + Px) ratio. Their average Ol/(Ol + Px) ratio matches EOCs better than UOCs. A principal component analysis (PCA) was performed illustrating that both the unknown degree of space weathering and the unknown regolith grain size on asteroid surfaces hinder the distinction between equilibrated and unequilibrated surfaces. Lastly, an anti-correlation between the diameter of the asteroids and their 1000 nm band depth is found indicating that larger sized S-type asteroids show finer grained surfaces.