¹Lydie Bonal et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115826]
¹Institut de Planétologie et d’Astrophysique, Université Grenoble Alpes, 38000 Grenoble, France
Copyright Elsevier

This paper is focused on the characterization of the thermal history of C-type asteroid Ryugu through the structure of the polyaromatic carbonaceous matter in the returned samples determined by Raman spectroscopy. Both intact particles and extracted Insoluble Organic Matter (IOM) from the two sampling sites on Ryugu have been characterized. The main conclusions are that (i) there is no structural difference of the polyaromatic component probed by Raman spectroscopy between the two sampling sites, (ii) in a manner similar to type 1 and 2 chondrites, the characterized Ryugu particles did not experience significant long-duration thermal metamorphism related to the radioactive decay of elements such as 26Al; (iii) some structural variability is nevertheless observed within our particle set. It can be interpreted as some particles having experienced some short-duration and weak heating (R3 in the scale defined by Quirico et al. 2018 and TII or lower according to the scale defined by Nakamura, 2005).

^1,2Elias Wölfer,^2,3Gerrit Budde,^1,2Thorsten Kleine
Geochimica et Cosmochmica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.10.010]
¹Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
²Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
³Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA
Copyright Elsevier

The carbonaceous Bencubbin-like (CB), high-metal (CH), and Renazzo-like (CR) chondrites are metal-rich chondrites that have been suggested to be genetically linked and are sometimes grouped together as the CR chondrite clan. Of these, the CB and CH chondrites are thought to have formed in an impact-generated vapor-melt plume from material that may be isotopically akin to CR chondrites. We report Mo, Ti, Cr, and Hf-W isotopic data for CB and CH chondrites in order to determine their formation time, to assess whether these chondrites are genetically related, and to evaluate their potential link to CR chondrites. An internal Hf-W isochron for the CH chondrite Acfer 182 yields an age of 3.8±1.2 Ma after formation of Ca-Al-rich inclusions, which is indistinguishable from the mean Hf-W model age for CB metal of 3.8±1.3 Ma. The Mo isotopic data for CB and CH chondrites indicate that both contain some of the same metal and silicate components, which themselves are isotopically distinct. As such, the different Mo isotopic compositions of bulk CB and CH chondrites reflect their distinct metal-to-silicate ratios. CR metal exhibits the same Mo isotopic composition as CB and CH metal, but CR silicates have distinct Mo and Ti isotopic compositions compared to CB and CH silicates, indicating that CB/CH chondrites may be genetically related to CR metal, but not to CR silicates. Together, the new isotopic data are consistent with formation of CB and CH chondrites in different regions of a common impact-generated vapor-melt plume and suggest that the CB and CH metal may derive from a metal-rich precursor genetically linked to CR chondrites. The Hf-W systematics of CH and CB chondrites indicate that the impact occurred at 3.8±0.8 Ma after the formation of Ca-Al-rich inclusions and, hence, up to ∼1 Ma earlier than previously inferred based on Pb-Pb chronology.

¹Nicolas Dauphas,¹Timo Hopp,²David Nesvorný
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115805]
¹Origins Lab, The University of Chicago, 5734 South Ellis Ave, Chicago, IL 60637, USA
²Department of Space Studies, Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, USA
Copyright Elsevier

Elements with differing siderophile affinities provide insights into various stages of planetary accretion. The isotopic anomalies they exhibit offer a deeper understanding of the materials responsible for the formation of terrestrial planets. By analyzing new iron isotopic anomaly data from Martian meteorites and drawing insights from published data for O, Ca, Ti, Cr, Fe, Ni, Sr, Zr, Mo, Ru, and Si, we scrutinize potential changes in the isotopic composition of the material accreted by Mars and Earth during their formation. Our methodology employs a Bayesian inference method, executed using a Markov Chain Monte Carlo (MCMC) algorithm.

The Bayesian method helps us balance the task of emulating the compositions of the terrestrial planets (reflected in the likelihood) with the flexibility to explore the isotopic compositions of mixing components within permissible intervals (indicated by the priors of the nuisance parameters). A Principal Component Analysis of isotopic anomalies in meteorites identifies three main clusters (forming the three parts of the isotopic trichotomy): CI, CC=CM + CO + CV + CR, and NC = EH + EL + H + L + LL. We adopt CI, COCV, O, and E as endmember compositions in the mixtures. We are concerned here with explaining isotopic anomalies in Mars and Earth, not their chemical compositions. Previous studies have shown that Earth’s chemical composition could not be well explained by solely considering undifferentiated meteorites, as it requires incorporation of a refractory component enriched in forsterite. The endmember chondrite components considered here are assumed to be representative of isotopic reservoirs that were present in the solar nebula, but the actual building blocks could have had different chemical compositions, and we use cursive letters to denote those putative building blocks

Because Earth’s mantle composition is an endmember for some isotopic systems, it cannot be reproduced exactly by considering known chondrite groups only and requires involvement of a component that is missing from meteorite collections but is likely close to enstatite meteorites. With this caveat in mind, our results suggest that Earth is primarily an isotopic mixture of ~92%, 6%, and < 2% and . Mars, on the other hand, appears to be a mixture of ~65% , 33% , and < 2% and . We establish that Earth’s contribution substantially increased during the latter half of its accretion. Mars began accreting a mix of and but predominantly accreted later. Mars’ changing isotopic makeup during accretion can be explained if it underwent gas-driven type I migration from its origin near the – boundary to a location well within the region during the first few million years of solar system history. Earth’s later increased contribution may be attributed to the stochastic impact of an interloper carbonaceous embryo that moved inside the inner solar system region while nebular gas was still present, and subsequently participated in the stage of chaotic growth. The discovery that a significant portion of Earth’s building blocks closely resembles enstatite chondrites contrasts with recent findings of Si isotopic anomalies in enstatite chondrites when compared to terrestrial rocks. We suggest this discrepancy likely stems from insufficient correction for high-temperature equilibrium isotopic fractionation, whether of nebular or planetary origin. With appropriate adjustments for this influence, both the silicate Earth and enstatite chondrites exhibit comparable Si isotopic anomalies, reaffirming a genetic link between them.

¹Peter L. Olson,¹Zachary D. Sharp
Earth and Planetary Science Letters 622, 118418 Link to Article [https://doi.org/10.1016/j.epsl.2023.118418]
¹Earth and Planetary Sciences, University of New Mexico, United States of America
Copyright Elsevier

We combine calculations of pebble accretion and accretion by large and giant impacts to quantify the effects of pebbles on the hafnium-tungsten system during Earth formation. Our models include an early pebble accretion phase lasting 4–6 Myr with a global magma ocean and core segregation, a 20–50 Myr phase of large impacts, and a late giant impact representing the Moon-forming event. We consider various mass additions during each accretion phase, vary the metal-silicate partition coefficient for tungsten over a wide range, and track Hf180, Hf182, W182 and W184 in proto-Earth and impactor models over time using standard chondritic values for these isotopes in the pebbles. We find that an early phase of pebble accretion is compatible with the tungsten anomaly of Earth’s early mantle as well as the present-day Hf/W ratio, but under restricted conditions. In particular, the pebble mass of proto-Earth is limited to 0.7 Earth masses or less, the average metal-silicate partition coefficient for tungsten is 30–50, and because the metal-silicate equilibration efficiency for giant impacts is low, the equilibration efficiency must be high for the large impactors.

¹David R. Frank,¹Gary R. Huss,²Michael E. Zolensky,¹Kazuhide Nagashima,³Loan Le
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14083]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, USA
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas, USA
³Jacobs JETS, Houston, Texas, USA
Published by arrangement with John Wiley & sons

Cosmochemists have relied on CI carbonaceous chondrites as proxies for chemical composition of the non-volatile elements in the solar system because these meteorites are fine-grained, chemically homogeneous, and have well-determined bulk compositions that agree with that of the solar photosphere, within uncertainties. Here we report the discovery of a calcium-aluminum-rich inclusion (CAI) in the Ivuna CI chondrite. CAIs are chemically highly fractionated compared to CI composition, consisting of refractory elements and having textures that either reflect condensation from nebular gas or melting in a nebular environment. The CAI we found is a compact type A CAI with typical 16O-rich oxygen. However, it shows no evidence of 26Al, which was present when most CAIs formed. Finding a CAI in a CI chondrite raises serious questions about whether CI chondrites are a reliable proxy for the bulk composition of the solar system. Too much CAI material would show up as mismatches between the CI composition and the composition of the solar photosphere. Although small amounts of refractory material have previously been identified in CI chondrites, this material is not abundant enough to significantly perturb the bulk compositions of CI chondrites. The agreement between the composition of the solar photosphere and CI chondrites allows no more than ~0.5 atom% of CAI-like material to have been added to CI chondrites. As the compositions of CI chondrites, carbonaceous asteroids, and the solar photosphere are better determined, we will be able to reduce the uncertainties in our estimates of the composition of the solar system.

¹Alexander N. Krot,²Tasha L. Dunn,³Michail I. Petaev,⁴Chi Ma,¹Kazuhide Nagashima,⁵Jutta Zipfel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14080]
¹Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Mānoa, Honolulu, Hawaii, USA
²Department of Geology, Colby College, Waterville, Maine, USA
³Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
⁴Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁵Senckenberg Gesellschaft für Naturforschung, Frankfurt am Main, Germany
Published by arrangement with John Wiley & Sons

We report on the primary and secondary mineralogies of three coarse-grained igneous calcium-aluminum-rich inclusions (CAIs) (Compact Type A [CTA], Type B [B], and forsterite-bearing type B [FoB]) from the Northwest Africa (NWA) 5343 (CK3.7) and NWA 4964 (CK3.8) carbonaceous chondrites, compare them with the mineralogy of igneous CAIs from the Allende (CV3.6) chondrite, and discuss the nature of the alteration processes that affected the CK and CV CAIs. The primary mineralogy and mineral chemistry of the CK3 CAIs studied are similar to those from Allende; however, primary melilite and anorthite are nearly completely absent. Although the secondary minerals identified in CK CAIs (Al-diopside, andradite, Cl-apatite, clintonite, forsterite, ferroan olivine, Fe,Ni-sulfides, grossular, ilmenite, magnetite, plagioclase, spinel, titanite, and wadalite) occur also in the Allende CAIs, there are several important differences: (i) In addition to melilite and anorthite, which are nearly completely replaced by secondary minerals, the alteration of CK CAIs also affected high-Ti pyroxenes (fassaite and grossmanite) characterized by high Ti³⁺/Ti⁴⁺ ratio and spinel. These pyroxenes are corroded and crosscut by veins of Fe- and Ti-bearing grossular, Fe-bearing Al,Ti-diopside, titanite, and ilmenite. Spinel is corroded by Fe-bearing Al-diopside and grossular. (ii) The secondary mineral assemblages of grossular + monticellite and grossular + wollastonite, commonly observed in the Allende CAIs, are absent; the Fe-bearing grossular + Fe-bearing Al-diopside ± Fe,Mg-spinel, Fe-bearing grossular + Fe,Mg-olivine ± Fe,Mg-spinel, and Ca,Na-plagioclase + Fe-bearing Al-diopside + Fe-bearing grossular assemblages are present instead. These mineral assemblages are often crosscut by veins of Fe-bearing Al-diopside, Fe,Mg-olivine, Fe,Mg-spinel, and Ca,Na-plagioclase. The coarse-grained secondary grossular and Al-diopside often show multilayered chemical zoning with distinct compositional boundaries between the layers; the abundances of Fe and Ti typically increase toward the grain edges. (iv) Sodium-rich secondary minerals, nepheline and sodalite, commonly observed in the peripheral portions of the Allende CAIs, are absent; Ca,Na-plagioclase is present instead. We conclude that coarse-grained igneous CAIs from CK3.7–3.8 s and Allende experienced an open-system multistage metasomatic alteration in the presence of an aqueous solution–infiltration metasomatism. This process resulted in localized mobilization of all major rock-forming elements: Si, Ca, Al, Ti, Mg, Fe, Mn, Na, K, and Cl. The metasomatic alteration of CK CAIs is more advanced and occurred under higher temperature and higher oxygen fugacity than that of the Allende CAIs.

¹Kevin Zahnle,²James F. Kasting
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.09.023]
¹NASA Ames Research Center, Mails Stop 245-3, Moffett Field, 94043, CA, USA
²The Pennsylvania State University, State College,, PA, USA
Copyright Elsevier

We develop a new model of diffusively modulated hydrodynamic escape to predict oxygen isotopic fractionations caused by the loss of water from a steam atmosphere of Venus. The chief technical advance over previous work is including CO₂ as a major species. We find that ordinary (�18O) and mass-independent (Δ17O) fractionations depend mostly on the extent of lithospheric buffering and the ferocity of EUV heating when escape took place, and relatively little on the size of the lost ocean(s). It is likely that Δ17O evolved significantly from its birth state, not only in the atmosphere but also in the silicates of the crust and upper mantle. If both �18O and Δ17O of Venus are identical to Earth and Moon, we may conclude that Venus and Earth accreted from a common pool. But differences in �18O and Δ17O can be attributed to escape rather than to genetics. If the differences are large enough, they can be used to constrain when escape took place and the extent of volatile exchange with the lithosphere. Neon and argon systematics are most consistent with minimal escape, especially if an Ar-rich source, possibly derived from comets, is added. However, we also find a novel class of solutions in which Ne and Ar of Venus, Earth, and Mars are evolved from a common source material subject to different vigors of hydrodynamic escape, least extreme for Earth and most extreme for Mars. These alternative models require that Venus was always rather dry (<10% of an Earth ocean) and its water lost very early (before <100 Myrs). The two styles of escape – minimal or extreme – should be readily distinguished by an unambiguous measurement of the Ar/Kr ratio. Finally, we find that predicted D/H enrichments are of order 100 for almost all model parameters. This result, a direct consequence of diffusion-limited escape of H and D, provides support for the overall scenario.

^1,2Elizaveta Kovaleva, ³Hassan Helmy, ^4,5Said Belkacim,²Anja Schreiber, ²Franziska D.H. Wilke,²Richard Wirth
American Mineralogist 108, 1906-1923 Link to Article [http://www.minsocam.org/msa/ammin/toc/2023/Abstracts/AM108P1906.pdf]
¹Department of Earth Sciences, University of the Western Cape, Robert Sobukwe Road, 7535 Bellville, South Africa
²Helmholtz Centre Potsdam—GFZ German Research Centre for Geosciences, Telegrafenberg, D-14473 Potsdam, Germany
³Department of Geology, Minia University, 61519-Minia, Egypt
⁴LAGAGE Laboratory, Department of Geology, Faculty of Sciences, Ibn Zohr University, P.O. Box 28/S, 80 000, Agadir, Morocco
⁵Research Institute on Mines and Environment (RIME), Université du Québec en Abitibi-Témiscamingue, 445 Boul. Université, Rouyn-Noranda, Québec J9X 5E4, Canada
Copyright: The Mineralogical Society of America

The origin of Libyan Desert Glass (LDG) found in the western parts of Egypt close to the Libyan
border is debated in planetary science. Two major theories of its formation are currently competing:
(1) melting by airburst and (2) formation by impact-related melting. While mineralogical and textural
evidence for a high-temperature event responsible for the LDG formation is abundant and convincing, minerals and textures indicating high shock pressure have been scarce. This paper provides a
nanostructural study of the LDG, showing new evidence of its high-pressure and high-temperature
origin. We mainly focused on the investigation of Zr-bearing and phosphate aggregates enclosed within
LDG. Micro- and nanostructural evidence obtained with transmission electron microscopy (TEM) are
spherical inclusions of cubic, tetragonal, and orthorhombic (Pnma or OII) zirconia after zircon, which
indicate high-pressure, high-temperature decomposition of zircon and possibly, melting of ZrO2. Inclusions of amorphous silica and amorphous Al-phosphate with berlinite composition (AlPO4) within
mosaic whitlockite and monazite aggregates point at decomposition and melting of phosphates, which
formed an emulsion with SiO2 melt. The estimated temperature of the LDG melts was above 2750 °C,
approaching the point of SiO2 boiling. The variety of textures with different degrees of quenching immediately next to each other suggests an extreme thermal gradient that existed in LDG through radiation
cooling. Additionally, the presence of quenched orthorhombic OII ZrO2 provides direct evidence of
high-pressure (>13.5 GPa) conditions, confirming theory 2, the hypervelocity impact origin of the LDG.

^1,2M.D. Suttle,²A.J. King,²C.S. Harrison,^1,3Q.H.S. Chan,⁴A. Greshake,⁵R. Bartoschewitz,⁶A.G. Tomkins,⁷T. Salge,²P.F. Schofield,²S.S. Russell
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.09.024]
¹School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
²Planetary Materials Group, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
³Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK
⁴Museum für Naturkunde, Leibniz-Institut für Evolutions und Biodiversitätsforschung, Invalidenstraße 43, 10115 Berlin, Germany
⁵Bartoschewitz Meteorite Laboratory, Weiland 37, D-38518 Gifhorn, Germany
⁶School of Earth, Atmosphere and Environment, Melbourne, Victoria, Australia
⁷Imaging and Analysis Centre, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
Copyright Elsevier

The CY chondrites are a group of thermally metamorphosed carbonaceous chondrites. Although they share similarities with the CM and CI chondrites, their primary properties argue for a distinct classification. Previous studies have highlighted their isotopically heavy bulk compositions (δ17O=10 ‰, δ18O=21 ‰, Δ17O=0 ‰) and exceptionally high sulphide abundances (10-30 vol%). In this work we explore their petrography and alteration history. The CYs accreted low abundances of chondrules (15-20 area%) with average apparent diameters slightly larger (∼320-340 µm) than the CM chondrites. In contrast to the CMs, the CYs record an early episode of brecciation prior to the main window of aqueous alteration. Subsequent fluid activity produced a range of alteration extents with both CY2 and CY1 chondrites documented. Phyllosilicate minerals in the CYs were a mix of serpentine and saponite (including occurrences of Na-saponite) with minor quantities of chlorite (within chondrules). An initial generation of Fe-sulphides formed by sulfidation of metal, and by precipitation from S-rich fluids. Three generations of carbonates are recognized, an early generation that infilled voids left by brecciation and co-precipitated with sulphide, a later generation that co-precipitated with magnetite and a final Fe-Mg-bearing generation which formed large (>100 µm) clasts. Only the first-generation carbonates are found in the CY2s, while the CY1s preserve all three generations. Phosphates occur as Ca-apatite or rarely as Mg-apatite and have hydroxylapatite compositions, indicating low halogen activities in the alteration fluids. Refractory oxides (ilmenite and Cr-spinel) occur as precipitates adhering to the margins of phyllosilicates. They formed late in the alteration sequence and attest to oxidizing conditions. During the late-stages of aqueous alteration Fe-sulphides were replaced by magnetite. Thermal metamorphism (Stage II-IV: ∼300-750 °C) overprinted aqueous alteration leading to dehydration and recrystallization of the phyllosilicate matrix and the decomposition of some carbonate phases. Most Fe-sulphide grains survived heating without decomposition as initial partial decomposition from pyrrhotite to troilite under closed system conditions led to elevated ƒS2 gas and resulted in a stabilizing effect. Retrograde reactions between trapped S2 gas and metal/magnetite formed a final generation of Fe-sulphides. The survival of Fe-sulphides and their stochiometric troilite compositions are evidence for near-closed system heating. Analysis of organic matter by Raman spectroscopy supports an interpretation of short-duration heating (on the scale of minutes to days), at peak temperatures between 750-900 °C. Thus, an impact event was the most likely cause of metamorphic heating.

^1,2S. S. Rout,³J. Storz,⁴A. Davydok,³A. Bischoff,⁵T. John,⁴C. Krywka,⁶M. Ritter
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14082]
¹School of Earth and Planetary Sciences, National Institute of Science Education and Research, Khorda, India
²Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, India
³Institut für Planetologie, University of Münster, Münster, Germany
⁴Institute of Materials Physics, Helmholtz-Zentrum Hereon, Outstation DESY, Hamburg, Germany
⁵Freie Universität Berlin, Institut für Geologische Wissenschaften, Berlin, Germany
⁶Electron Microscopy Unit, Hamburg University of Technology, Hamburg, Germany
Published by arrangement with John Wiley & Sons

The origin of diamond in ureilites has been frequently debated. We investigated carbon phase assemblages (CPAs) in five ureilitic samples of the brecciated asteroid 2008 TC3, found within the Almahata Sitta (AHS) strewn field, by transmission electron microscopy, Raman spectroscopy, synchrotron X-ray diffraction, and cathodoluminescence. Samples MS-MU 006, MS-187, and MS-170, are of low to moderate shock degree (U-S2 and U-S3), and samples MS-MU 027 (U-S4) and MS-MU 045 (U-S5) have a higher shock degree. In MS-MU 006 and MS-187, we did not find any diamond grains. MS-170 contains disordered and distorted graphite with diamond grains up to 12 μm in size and containing inclusions of Fe,Ni-metal, FeS, Fe-phosphide, and Cr,Fe-oxide. These diamond grains formed under relatively low (5–15 GPa) shock pressures through a catalytic process in the presence of a Fe,Ni,Cr,S,P-rich melt. The highly shocked and fine-grained ureilites MS-MU 027 and MS-MU 045 have three different types of CPAs, namely a nanopolycrystalline assemblage of diamond and defect-rich diamond/lonsdaleite, disordered and distorted graphite, and polycrystalline diamond with abundant Fe-rich mineral inclusions. The CPAs that have only diamond and planar defect-rich diamond (e.g., MS-MU 027) most likely formed through martensitic transformation of graphite to diamond and lonsdaleite at >15 GPa and >2000 K. The assemblage of diamond, defect-rich diamond, and disordered and distorted graphite (e.g., MS-MU 045) formed by martensitic transformation of graphite to diamond and lonsdaleite, followed by back-transformation to disordered graphite. We did not find any conclusive evidence to support the formation of diamond grains under high static pressure.