Earliest Evidence of Nebular Shock Waves Recorded in a Calcium-Aluminum-rich Inclusion

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.

16O-rich anhydrous silicates in CI chondrites: Implications for the nature and dynamics of dust in the solar accretion disk

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.

Nickel-rich, volatile depleted iron meteorites: Relationships and formation processes

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.

On the nature of oxygen-isotope heterogeneity of igneous calcium-aluminum-rich inclusions in cv carbonaceous chondrites

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.

Fe5S2 identified as a host of sulfur in Earth and planetary cores

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.

Campo del Cielo modeling and comparison with observations: I. Atmospheric entry of the iron meteoroid

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.

Slow cooling during crystallisation of barred olivine chondrules

1François Faure,1Marion Auxerre,1Valentin Casola
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.epsl.2022.117649]
1Université de Lorraine, CNRS, CRPG, UMR 7358, 15 rue Notre Dame des Pauvres, F-54501 Vandoeuvre-lès-Nancy, France
Copyright Elsevier

Barred olivine (BO) chondrules are small ferromagnesian silicate igneous droplets with unique dendritic textures that are considered to have formed in the early solar system during one or more brief high-temperature episodes, followed by rapid cooling in a gas. Rapid cooling rates of 100–7200 °C/h during chondrule formation have been proposed based on experiments attempting to reproduce BO crystal textures. However, the BO texture has never truly been reproduced under such rapid cooling conditions. Here, we experimentally show that true BO textures can be produced either after rapid cooling (>50 °C/h) following by reheating step or by cooling rates slower than 10 °C/h. Regardless of the thermal history considered, the chemical compositions of glass inclusions trapped within olivines of BO chondrules imply a final slow cooling rate one to two orders of magnitude below previous estimates. Such slow cooling rates are consistent with those estimated for plagioclase-bearing porphyritic chondrules and magmatic type-B Ca-Al-rich inclusions, suggesting that slow cooling rates are common to all similar chondritic objects.

IVA iron meteorites as late-stage crystallization products affected by multiple collisional events

1,2Alan E.Rubin,1Bidong Zhang,3Nancy L.Chabot
Geochimica et Cosmocchimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.05.020]
1Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
2Maine Mineral & Gem Museum, 99 Main Street, P.O. Box 500, Bethel, ME 04217, USA
3Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
Copyright Elsevier

Although IVA irons have O- and Cr-isotopic compositions resembling those of equilibrated LL chondrites, the bulk composition of refractory elements (e.g., Re, Ir, Pt) in the IVA core appears to be significantly lower than LL. These compositional discrepancies suggest known IVA irons may be missing early crystallized samples. We hypothesize the bulk composition of the IVA core is LL-like, but current collections do not include early fractional-crystallization IVA products. Our fractional-crystallization modeling of element vs. Au trends suggests that extant IVA irons are products of > 40% crystallization of the core, assuming an initial 2.9 wt.% S content. The model-derived bulk (Ni-normalized) composition of the IVA core is depleted relative to LL in most moderate volatiles: S (82% depletion), Ge (99.9% depletion), Ga (95% depletion), As (50% depletion); however, Au is enriched by 10%. Because moderate volatiles with depletions > 80% relative to LL have 50%-condensation temperatures < 1,020 K, it seems likely these depletions reflect post-accretion impact-induced volatilization of the IVA asteroid. The mean Ni-normalized compositions of analyzed IVA irons yield a lesser depletion of As (30%) and greater enrichment of Au (48%) relative to LL. The IVA asteroid may have experienced a complex parent-body thermal and collisional history: (1) differentiation, (2) impact-induced mantle stripping, devolatilization, and fractional condensation, (3) rapid crystallization of the core from the outside inwards, (4) shattering of the core after ∼75% crystallization, (5) quenching of thinly insulated samples (e.g., Fuzzy Creek), (6) formation of amorphous free silica in several IVA irons after impact-induced vaporization of portions of the overlying silicate mantle, followed by fractional condensation, (7) loss of portions of the core representing the first 40% of crystallization, (8) reaccretion of some core fragments, facilitating relatively slow cooling of a few IVA irons (e.g., Duchesne, Duel Hill (1854), Chinautla), and (9) collisional resetting of the Re-Os clock 4456 ± 25 Ma ago.

Statistical analysis of APXS-derived chemistry of the clay-bearing Glen Torridon region and Mount Sharp group, Gale crater, Mars

1C. D. O’Connell-Cooper,1L. M. Thompson,1J. G. Spray,2J. A. Berger,3R. Gellert,3M. McCraig,4S. J. VanBommel,5A. Yen
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007177]
1Planetary and Space Science Centre, University of New Brunswick, Fredericton, Canada
2NASA Johnson Space Center, Houston, TX, USA
3University of Guelph, Ontario, Canada
4Washington University, St Louis, MO, USA
5Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
Published by arrangement with John Wiley & Sons

The Glen Torridon stratigraphic sequence marks the transition from the low energy lacustrine-dominated Murray formation (Mf) (Jura member: Jm) to the more diverse Carolyn Shoemaker formation (CSf) (Knockfarril Hill member: Knockfarril Hill; Glasgow member: Glasgow). This transition defines a change in depositional setting. Alpha Particle X-ray Spectrometer (APXS) results and statistical analysis reveal that the bulk primary geochemistry of Mf targets are broadly in family with CSf targets, but with subtle compositional and diagenetic trends with increasing elevation. APXS results reveal significant compositional differences between Jura_GT and the stratigraphically equivalent Jura on Vera Rubin ridge (Jura_VRR). The data define two geochemical facies (high-K or high-Mg), with a strong bimodal grain distribution in Jura_GT and Knockfarril Hill. The contact between Knockfarril Hill and Glasgow is marked by abrupt sedimentological changes but a similar composition for both. Away from the contact, the Knockfarril Hill and Glasgow plot discretely, suggesting a zone of common alteration at the transition and/or a gradual transition in provenance with increasing elevation in the Glasgow member. APXS results point to a complex history of diagenesis within Glen Torridon, with increasing diagenesis close to the Basal Siccar Point unconformity on the Greenheugh pediment, and with proximity to the beginning of the clay sulfate transition. Elemental mobility is evident in localized enrichments or depletions in Ca, S, Mn, P, Zn, Ni. The highly altered Hutton interval, in contact with the unconformity on Tower butte, is also identified on Western Butte, indicating that the “interval” was once laterally extensive.