¹John P.Bradley,¹Hope A.Ishii,²Karen Bustillo,²James Ciston,³Ryan Ogliore,^4,5Thomas Stephan,⁶Donald E.Brownlee,⁶David J.Joswiak
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.036]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai ‘i at Mānoa, 1680 East-West Road, Honolulu, HI 96822, USA
²National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
³Laboratory for Space Sciences, Washington University, St. Louis, MO 63130, USA
⁴Department of Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
⁵Chicago Center for Cosmochemistry, Chicago, IL, USA
⁶Department of Astronomy, University of Washington, Seattle WA 98195, USA
Copyright Elsevier

The provenance of GEMS (glass with embedded metal and sulfides) in cometary type interplanetary dust particles is investigated using analytical scanning transmission electron microscopy and secondary ion mass spectrometry. We review the current state of knowledge and closely examine the densities, elemental compositions and distributions, iron oxidation states, and isotopic compositions of a subset of GEMS in chondritic porous interplanetary dust. We find that GEMS are underdense with estimated densities that are 35–65% of compositionally equivalent crystalline aggregates. GEMS low densities result in a lower contribution to the bulk compositions of IDPs than has been assumed based on their volume fraction. We also find that element/Si ratios, assumed to be primary (indigenous), are instead perturbed by contamination and secondary alteration, including pulse heating during atmospheric entry. Fe in pyrrhotite inclusions was oxidized and Mg, S, Ca, and Fe were depleted relative to lithophile Al and Si, resulting in reduction in element/Si ratios. Because they trap outgassing elements, Fe-rich oxide rims that formed on the surface of GEMS are serendipitous “witness plates” to the changes in composition that accompany atmospheric entry. As a result of alteration, GEMS elemental compositions cannot reliably inform about their provenance. Except for highly anomalous oxygen isotope ratios measured in some large GEMS grains that indicate a contribution from circumstellar dust, oxygen isotope compositions are generally poor indicators of provenance. Prior work indicates that most GEMS fall close to the terrestrial oxygen isotope composition, which, however, does not exclude a presolar interstellar origin. Nitrogen isotopic compositions are more diagnostic. Elevated 15N/14N ratios indicate that GEMS accreted in conjunction with formation of organic matter by ion–molecule reactions in a cold (<50 K) presolar environment like the extreme outer nebula or interstellar medium. Considering all observations, we conclude that GEMS are most likely processed interstellar silicates.

^1,2L.Folco,³L.Carone,^1,2M.D’Orazio,⁴C.Cordier,^5,1M.D.Suttle,⁶M.van Ginneken,^1,2M.Masotta
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.035]
¹Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, Pisa, Italy
²CISUP, Centro per la Integrazione della Strumentazione dell’Università di Pisa, Lungarno Pacinotti, Pisa, Italy
³Università di Camerino, Scuola di Scienze e Tecnologie, Sezione di Geologia, Via Gentile III da Varano 7, 62032 Camerino, Italy
⁴Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France
⁵School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁶Centre for Astrophysics and Planetary Science, School of Physical Sciences, Ingram Building, University of Kent, Canterbury CT2 7NH, UK
Copyright Elsevier

Kamil crater (Egypt) is a natural laboratory for the study of processes and products associated with the impacts of small iron projectiles on the Earth’s crust. In particular, because of the distinctive composition of the impactor (an ungrouped Ni-rich ataxite) and the target (Cretaceous sandstones and minor wackes) it offers a unique opportunity to study impactor–target physical–chemical interactions. Continuing the study of impact melt ejecta, we investigated the mineralogy and geochemistry of 25 Fe-Ni spherules – representative of a suite of 135 – recovered from the soil around the crater. Samples were collected during our 2010 geophysical expedition and investigated by combining scanning electron microscope imaging, electron probe microanalyzer and Raman spectroscopy analyses. Spherules range in size from 100 to 500 µm and show a variety of dendritic textures and mineral compositions dominated by Fe-Ni oxides of the wüstite – bunsenite and magnetite – trevorite series or Fe-Ni metal. All these features indicate quenching of high temperature (1600–1500 °C) oxide or metal liquid droplets under varying oxidizing conditions. A geochemical affinity with the iron impactor recorded by the Fe, Co, Ni ratios in the constituent phases (average Ni/Co element ratio of 25.1 ± 7.6; average Ni/(Ni + Fe) molar ratio of 0.21 ± 0.13), combined with target contamination (i.e., the ubiquitous occurrence of Si and Al from trace to minor amounts), document their origin as impact melt spherules formed through the physical and chemical interaction between metal projectile and silicate target melts and air. We propose a petrogenetic model that envisions formation as liquid droplet residues of immiscible projectile in a mixed silicate melt and their subsequent separation as individual spherules by stripping during hypervelocity ejection. We also argue that this model applies to all impact events produced by small iron projectiles and that such individual Fe-Ni oxide and metal spherules should be common impact products, despite little documentation in the literature. Our detailed mineralogical and geochemical characterization will facilitate their distinction from other, similar spherules of different origin (cosmic spherules, ablation spherules) often encountered in the geologic record.

¹Andrew K. Matzen,²Alan Woodland,³John R. Beckett,¹Bernard J. Wood
American Mineralogist 107, 1442-1452 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2022/Abstracts/AM107P1442.pdf]
¹Department of Earth Sciences, University of Oxford, Oxford, OX1 3AN, U.K.
²Goethe-Universität Institut für Geowissenschaften, Frankfurt, D-60438, Germany
³California Institute of Technology, MC 170-25, Pasadena, California 91125, U.S.A.
Copyright: The Mineralogical Society of America

We performed a series of experiments at 1 atm pressure and temperatures of 1300–1500 °C to
determine the effect of oxygen fugacity on the oxidation state of Fe in a synthetic martian basalt. Ferricferrous ratios were determined on the quenched glasses using Mössbauer spectroscopy. Following the conventional doublet assignments in the spectrum, we obtain a Fe3+/ΣFe value of 0.19 at 1450 °C and
an oxygen fugacity corresponding to the QFM buffer. If we apply the Berry et al. (2018) assignments
the calculated Fe3+/ΣFe drops to 0.09, and the slope of log(XFe melt O1.5/XFe melt O) vs. log( fO2) changes from 0.18 to 0.26.
Combining oxidation state data together with results of one additional olivine-bearing experiment
to determine the appropriate value(s) for the olivine (Ol)-liquid (liq) exchange coefficient, KD,Fe2+-Mg
= (FeO/MgO)Ol/(FeO/MgO)liq (by weight), suggests a KD,Fe2+-Mg of 0.388 ± 0.006 (uncertainty is one
median absolute deviation) using the traditional interpretation of Mössbauer spectroscopy and a value
of 0.345 ± 0.005 following the Mössbauer spectra approach of Berry et al. (2018).
We used our value of KD,Fe2+-Mg to test whether any of the olivine-bearing shergottites represent liquids.
For each meteorite, we assumed a liquid composition equal to that of the bulk and then compared that
liquid to the most Mg-rich olivine reported. Applying a KD,Fe2+-Mg of ~0.36 leads to the possibility that
bulk Yamato 980459, NWA 5789, NWA 2990, Tissint, and EETA 79001 (lithology A) represent liquids.

Cosmochemistry Papers will be on Summer Break for the next four weeks. We will commence operations again on July, 25th.

^1,2Prajkta Mane,³Shawn Wallace,²Maitrayee Bose,¹Paul Wallace,²Meenakshi Wadhwa,¹Juliane Weber,^1,4Thomas J.Zega
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.006]
¹Lunar and Planetary Laboratory, University of Arizona, 85721, Tucson, AZ, USA
²School of Earth and Space Exploration, Arizona State University, 87287, Tempe, AZ, USA
³EDAX, Ametek, Materials Analysis Division, 07430, Mahwah, USA
⁴Dept. of Materials Science and Engineering, University of Arizona, 85721, Tucson, USA
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) and chondrules are among the most predominant chondritic components contained within primitive meteorites. As CAIs are the first solids to form in the solar nebula, they contain a record of its earliest chemical and physical processes. Here we combine electron backscatter diffraction (EBSD) and 26Al-26Mg chronology techniques to determine the crystallographic properties and ages of CAI components that provide temporal as well as spatial constraints on their origins and subsequent processing in the solar protoplanetary disk. We find evidence of shock deformation within a CAI, suggesting that it was deformed as a free-floating object soon after the CAI formation at the beginning of the Solar System. Our results suggest that even though CAIs and chondrules formed in distinct environments and on different timescales, they were likely affected by similar shock processes that operated over large temporal (0 to ∼4 Ma) and spatial (0.2 to at least 2 to 3 au) extents. Our results imply that nebular shock events were active on a wider scale in the solar protoplanetary disk than previously recognized.

¹Gatien L.F.Morin,¹Yves Marrocchi,¹Johan Villeneuve,²Emmanuel Jacquet
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.017]
¹Université de Lorraine, CNRS, CRPG UMR 7358, Vandoeuvre-lès-Nancy, 54501, France
²IMPMC, CNRS & Muséum national d’Histoire naturelle, UMR 7590, CP52, 57 rue Cuvier, 75005 Paris, France
Copyright Elsevier

CI chondrites have nonvolatile chemical compositions closely resembling that of the Sun’s photosphere and are thus considered to have the most primitive compositions of all known solar system materials. They have, however, experienced pervasive parent-body alteration processes that transformed their primary constituents, obscuring the nature and origin of primordial CI dust. We used in-situ quantitative microprobe and secondary ion mass spectrometry techniques to characterize the chemistry and oxygen isotopic compositions of anhydrous silicates in two sections of the CI chondrites Ivuna and Alais, which contain higher abundances of those than other CI samples. These silicates are Mg-rich olivine and low-Ca pyroxene crystals mostly occurring as aggregates within sub-mm Fe-rich clasts. Our data reveal mass-independent oxygen isotopic variations with Δ17O values ranging from −23.63 to −0.57‰, representing the first evidence of extremely 16O-rich (Δ17O < −20‰) olivine and pyroxene grains in CI chondrites. Two of these olivines are characterized by MnO/FeO ∼ 1, typical of low-iron, Mn-enriched silicates commonly observed in amoeboid olivine aggregates. Other anhydrous silicate grains have Δ17O values ranging from −6 to 0‰, probably representing chondrule fragments. Combined, these results indicate that chondrule and refractory inclusion material were incorporated into the CI parent body(ies). This conclusion is consistent with recent models showing that refractory inclusions could have formed and/or been transported at larger heliocentric distances than previously thought during the concomitant injection of material from the molecular cloud and outward extension of the disk by viscous spreading. The CI chondrules are presumably of local origin, with their isotopic systematics suggesting an affinity with the CR clan.

¹C.M.Corrigan,²K.Nagashima,^3,6C.Hilton,¹T.J.McCoy,³R.D.Ash,⁴H.A.Tornabene,³R.J.Walker,³W.F.McDonough,⁵D.Rumble
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.008]

¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, 10th Street and Constitution Ave. NW, Washington, DC 20560 USA
²Hawai‘i Institute of Geology and Planetology, University of Hawai’i at Manoa, 2020 Correa Rd, Honolulu, HI 96822 USA
³Department of Geology, University of Maryland , College Park, MD 20742 USA
⁴Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854 USA
⁵Carnegie Institution for Science, Earth and Planets Laboratory, 5241 Broad Branch Road NW, Washington DC 20015 USA
⁶Environmental Signatures Team, Pacific Northwest National Laboratory, Richland, WA 99354 USA
Copyright Elsevier

Ungrouped iron meteorites Tishomingo, Willow Grove, and Chinga, and group IVB iron meteorites, are Ni-rich. Similarities include enrichments of 10-100 × CI for some refractory siderophile elements, and equivalent depletions in more volatile siderophile elements. Superimposed on the overall enrichment/depletion trend, certain siderophile elements (P, W, Fe, Mo) are depleted relative to elements of similar volatility. All three ungrouped irons derive from parent bodies formed in the early Solar System. Willow Grove and Chinga are characterized by cosmic ray exposure corrected ¹⁸²W/¹⁸⁴W consistent with metal-silicate segregation on their parent bodies within 1-3 Myr of Solar System formation, within the age range determined for segregation of magmatic iron meteorite parent bodies, including group IVB irons. Tishomingo is characterized by a younger model age 4-5 Myr subsequent to Solar System formation, reflecting either late stage melting resulting from ²⁶Al decay, or an impact resetting. The discovery of stishovite in Tishomingo, indicating exposure to a minimum shock pressure of 8-9 GPa, is consistent with the latter.

Stishovite in Tishomingo and chromite included in troilite-daubréelite in IVB irons allows oxygen isotopic composition comparison between these meteorites. Different mass independent oxygen isotopic compositions of IVB irons and Tishomingo indicate genetically distinct parent bodies. By contrast, mass independent Mo isotopic compositions overlap within analytical uncertainties, indicating a similar, carbonaceous chondrite (CC) type genetic heritage. Molybdenum and ¹⁸³W isotopic data for Chinga and Willow Grove indicate derivation from CC type parent bodies. Willow Grove shares Mo and ¹⁸³W isotopic compositions with the Ni-rich South Byron Trio (SBT) grouplet and the Milton pallasite. These Ni-rich meteorites likely formed in the same general nebular environment as other CC planetesimals, likely the outer Solar System.

Highly siderophile element (HSE) abundances of Willow Grove and Tishomingo are similar to some IVB meteorites, consistent with formation by moderate degrees of fractional crystallization from initial metallic melts with low S and P, and modestly fractionated HSE. The comparable HSE abundances of Tishomingo and Willow Grove to some IVB irons, yet substantially higher Ni concentrations, indicate formation on parent bodies with lower bulk HSE abundances or HSE concentration in proportionally smaller volumes of metal. HSE abundances in Chinga are considerably lower than in IVB irons, highly fractionated, and processes responsible for these remain elusive.

For IVB irons and these ungrouped irons, high temperature condensation likely dominated the enrichment and depletion of the refractory and volatile siderophile elements, respectively. Parent body degassing may have also played a role. Relative depletion of volatile siderophile elements is not, however, a universal feature of high-Ni meteorites. The SBT and Milton pallasite are Ni-rich, but less depleted in the more volatile siderophile elements. Nickel enrichment was likely driven by oxidation of Fe metal during parent body accretion or core segregation. Oxidation of the Tishomingo and Willow Grove parent bodies may have occurred at ∼IW+1, indicated by relative Mo and W depletions due to metal/water reaction during differentiation. Late-stage reduction, indicated by the presence of Cr-bearing sulfides in Tishomingo and IVB irons, may have resulted from exhaustion of the oxidant.

¹Alexander N.Krot,¹Kazuhide Nagashima,²Glenn J.MacPherson,³Alexander A.Ulyanov
Geochimica et Cosmochimica Act a(in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.013]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822, USA
²Department of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, USA
³Department of Geology, Moscow State University, Moscow, 119992, Russia
Copyright Elsevier

Coarse-grained igneous Ca,Al-rich inclusions (CAIs) in CV (Vigarano group) carbonaceous chondrites have typically heterogeneous O-isotope compositions with melilite, anorthite, and high-Ti (>10 wt% TiO2) fassaite being 16O-depleted (Δ17O up to ∼ −3±2‰) compared to hibonite, spinel, low-Ti (<10 wt% TiO2) fassaite, Al-diopside, and forsterite, all having close-to-solar Δ17O ∼ −24±2‰. To test a hypothesis that this heterogeneity was established, at least partly, during aqueous fluid-rock interaction, we studied the mineralogy, petrology, and O-isotope compositions of igneous CAIs CG-11 (Type B), TS-2F-1, TS-68, and 818-G (Compact Type A), and 818-G-UR (davisite-rich) from Allende (CV>3.6), and E38 (Type B) from Efremovka (CV3.1−3.4). Some of these CAIs contain (i) eutectic mineral assemblages of melilite, Al,Ti-diopside, and ±spinel which co-crystallized and therefore must have recorded O-isotope composition of the eutectic melt; (ii) isolated inclusions of Ti-rich fassaite inside spinel grains which could have preserved their initial O-isotope compositions, and/or (iii) pyroxenes of variable chemical compositions which could have recorded gas-melt O-isotope exchange during melt crystallization and/or postcrystallization exchange controlled by O-isotope diffusivity. If these CAIs experienced isotopic exchange with an aqueous fluid, O-isotope compositions of some of their primary minerals are expected to approach that of the fluid.

We find that in the eutectic melt regions composed of highly-åkermanitic melilite (Åk65−71), anorthite, low-Ti fassaite, and spinel of E38, spinel, fassaite, and anorthite are similarly 16O-rich (Δ17O ∼ −24‰), whereas melilite is 16O-poor (Δ17O ∼ −1‰). In the eutectic melt regions of CG-11, spinel and low-Ti fassaite are 16O-rich (Δ17O ∼ −24‰), whereas melilite and anorthite are 16O-poor (Δ17O ∼ −3‰). In TS-2F-1, TS-68, and 818-G, melilite and high-Ti fassaite grains outside spinel have 16O-poor compositions (Δ17O range from −12 to −3‰); spinel is 16O-rich (Δ17O ∼ −24‰); perovskite grains show large variations in Δ17O, from −24 to −1‰. Some coarse perovskites are isotopically zoned with a 16O-rich core and a 16O-poor edge. Isolated high-Ti fassaite inclusions inside spinel grains are 16O-rich (Δ17O ∼ −24‰), whereas high-Ti fassaite inclusions inside fractured spinel grains are 16O-depleted: Δ17O range from −12 to −3‰. In 818-G-UR, davisite is 16O-poor (Δ17O ∼ −2‰), whereas Al-diopside of the Wark-Lovering rim is 16O-enriched (Δ17O < −16‰). On a three-isotope oxygen diagram, the 16O-poor melilite, anorthite, high-Ti fassaite, and davisite in the Allende CAIs studied plot close to O-isotope composition of an aqueous fluid (Δ17O ∼ −3±2‰) inferred from O-isotope compositions of secondary minerals resulted from metasomatic alteration of the Allende CAIs. We conclude that CV igneous CAIs experienced post-crystallization O-isotope exchange that most likely resulted from an aqueous fluid-rock interaction on the CV asteroid. It affected melilite, anorthite, high-Ti fassaite, perovskite, and davisite, whereas hibonite, spinel, low-Ti fassaite, Al-diopside, and forsterite retained their original O-isotope compositions established during igneous crystallization of CV CAIs. However, we cannot exclude some gas-melt O-isotope exchange occurred in the solar nebula. This apparently “mineralogically-controlled” exchange process was possibly controlled by variations in oxygen self-diffusivity of CAI minerals. Experimentally measured oxygen self-diffusion coefficients in CAI-like minerals are required to constrain relative roles of O-isotope exchange during aqueous fluid-solid and nebular gas-melt interaction.

¹Claire C.Zurkowski,^2,3Barbara Lavina,¹Abigail Case,¹Kellie Swadba,²Stella Chariton,^1,2Vitali Prakapenk,¹Andrew J.Campbell
Earth and Planetary Science Letters 593, 117650 Link to Article [https://doi.org/10.1016/j.epsl.2022.117650]
¹University of Chicago, Department of the Geophysical Sciences, 5734 S Ellis Ave, Chicago, IL 60637, USA
²Center for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60439, USA
³Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA
Copyright Elsevier

Cosmochemical considerations suggest that sulfur is a candidate light alloying element in rocky planetary cores, such that the high pressure-temperature (P-T) Fe-S phase relations likely play a key role in planetary core crystallization thermodynamics. The iron-saturated Fe-S phase relations were investigated to 200 GPa and 3250 K using combined powder and single-crystal X-ray diffraction techniques in a laser-heated diamond anvil cell. Upon heating at 120 GPa, I-4 Fe3S is observed to break down to form iron and a novel hexagonal Fe5S2 sulfide with the Ni5As2 structure (P6, ). To 200 GPa, Fe5S2 and Fe are observed to coexist at high temperatures while Fe2S polymorphs are identified with Fe at lower temperatures. An updated Fe-rich Fe-S phase diagram is presented. As this hexagonal Fe5S2 expresses complex Fe-Fe coordination and atomic positional disorder, crystallization of Fe5S2 may contribute to intricate elastic and electrical properties in Earth and planetary cores as they crystallize over time. Models of a fully crystallized Fe-rich Fe-S liquid in Earth’s and Venus’ core establish that Fe5S2 is likely the only sulfide to crystallize and may deposit in the outer third of the planets’ cores as they cool. Fe5S2 could further serve as a host for Ni and Si as has been observed in the related meteoritic phase perryite, (Fe, Ni)8(P, Si)3, adding intricacies to elemental partitioning during core crystallization. The stability of Fe5S2 presented here is key to understanding the role of sulfur in the crystallization sequences that drive the geodynamics and dictate the structures of Earth and rocky planetary cores.

¹A. Schmalen,¹R. Luther,^1,2,3N. Artemieva
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13832]
¹Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity Science, Berlin, 10115 Germany
²Planetary Science Institute, Tucson, Arizona, 85719 USA
³Institute for Dynamics of Geospheres, Russian Academy of Sciences, Moscow, 117049 Russia
Published by arrangement with John Wiley & Sons

This paper presents an attempt to reconstruct the Campo del Cielo (CdC) impact event, that is, to estimate the preatmospheric mass and velocity of the iron meteoroid and pre-impact parameters of its fragments allowing formation of funnels and impact craters. The goal of this study is to improve the understanding of the effects small-scale iron meteoroids can have on the Earth’s surface. We model the meteoroid’s atmospheric flight taking deceleration, ablation, and fragmentation into account, and then compare the results with available observations. We found that a fragment’s velocity near the surface should be <1 km s−1 in order to form a funnel with an intact meteorite inside. The estimates of preatmospheric (at an altitude of 100 km) parameters of the CdC impact event are as follows: minimal mass of 7500–8500 t, which corresponds to a diameter range of 12.2–12.8 m; maximum entry angle above the atmosphere of ~16.5° and velocities of 14.5–18.4  km s−1, which is close to the one most frequently reached by near-Earth objects (NEOs). Near the surface, the largest fragments with a mass of 400–1500 t and velocities of 4–7 km s−1 form impact craters whereas fragments with a mass <31 t and velocities <1 km s−1 form funnels. Masses <3 t are not included in our simulations. Their total mass is 280–460 t at the point of disruption but <110 t on the Earth’s surface. These numerous small fragments are dispersed over a large area and are very popular among meteorite hunters and dealers. In spite of all the observed crater location/size data and impactor velocity limits from the models, there are far more free parameters than constraints. As a result, any values for preatmospheric mass, velocity, and entry angle are merely representative or limitative as opposed to true values.