¹E. Dobrică,²J. A. Nuth,³A. J. Brearley
Meteoritics&Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13765]
¹Hawai’i Institute of Geophysics and Planetology, School of Ocean, Earth Science, and Technology, University of Hawai’i at Mānoa, Honolulu, Hawaii, 96822 USA
²Solar System Exploration Division, Code 690, NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
³Department of Earth and Planetary Sciences, MSC03-2040, 1 University of New Mexico, Albuquerque, New Mexico, 87131–0001 USA
Published by arrangemengt with Jophn Wiley & Sons

In order to understand the effects of the earliest fluid-assisted hydration processes on asteroids, we performed one hydrothermal experiment using three different reactants (FeO-rich amorphous silicates, iron metal powder, and water) at conditions informed by our current state of knowledge of asteroidal alteration. This experiment provides, for the first time, clear evidence that the growth of fayalite can occur during hydrothermal alteration, as described previously in meteorites. These newly formed fayalite crystals are elongated and porous, similar to the ones described in CV3, CK, and ordinary chondrites. The results show that (1) fayalite could form even if chemical equilibrium was not reached in the experiment, at a water to rock mass ratio (0.4 W/R at the beginning of the experiment) higher than the values calculated to be thermodynamically viable at equilibrium (W/R > 0.2); (2) the composition and the texture of the reactants changed during the hydrothermal alteration process, suggesting that the reactants, especially the amorphous silicates, underwent dissolution and reprecipitation; (3) fayalite can form at low temperature (220 °C), which is at the transition between hydrothermal alteration and fluid-assisted metamorphism in chondrites. The results are consistent with previous mineralogical observations and thermodynamic models, which suggest that fayalite crystals are formed on asteroidal parent bodies by the interaction between a hydrothermal fluid and disequilibrium assemblages that compose the pristine materials that condensed in the early solar nebula. This experiment suggests that two variables play a very important role in the formation of fayalite during the hydrothermal growth (W/R mass ratio and the fluid composition). These results are similar to the recent observations of the fine-grained matrix of ordinary chondrites.

¹C. A. Lorenz,¹E. V. Korochantseva,¹M. A. Ivanova,²J. Hopp,³I. A. Franchi,⁴M. Humayun,¹M. O. Anosova,¹S. N. Teplyakova,²M. Trieloff
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13774]
¹Vernadsky Institute RAS, Kosygin St. 19, Moscow, 119991 Russia
²Institut für Geowissenschaften, Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, Im Neuenheimer Feld 234-236, Heidelberg, 69120 Germany
³Planetary & Space Sciences, School of Physical Sciences, Open University, Milton Keynes, MK7 6AA UK
⁴National High Magnetic Field Laboratory and Department of Earth, Ocean & Atmospheric Science, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, Florida, 32310 USA
Published by arrangement with John Wiley & Sons

We report the results of petrological, geochemical, and geochronological investigations of the unusual K-rich L chondrite melt rock Northwest Africa 6486 (NWA 6486). The rock has slightly fractionated siderophile elements and a mostly unfractionated L chondrite pattern of lithophile elements with the exceptions of enrichments in K and Rb and chondritic Sr abundance similar to the K-rich inclusions found in the ordinary chondrites and indicating a fractionation of alkaline elements through the vapor. We suggest that NWA 6486 and related K-rich chondritic inclusions were formed in situ on the OC parent bodies and that K and Rb enrichment of these rock most probably is a result of the selective impact evaporation of volatile alkali elements followed by the reaction of a vapor with shock melt. NWA 6486 recorded a breakup event of the L chondrite parent asteroid at 470 Ma during which it was formed. Unusual veins, depleted in K, Na, Ca, and Al relative to the host rock were found in NWA 6486. We suggest that NWA 6486 was affected by aqueous fluids that produced alteration zones depleted in a feldspar component on the walls of opened fractures. The melt veins could be formed during a subsequent impact event by in situ melting of the fracture walls or due to decomposition of an injected supercritical aqueous silicate fluid. The aqueous alteration and the second impact event had no detectable effect on Ar and oxygen isotopic systems. Cosmic ray exposure ages indicate that NWA 6486 was ejected from its parent asteroid ~3–4 Ma ago.

¹G.J.MacPherson,²A.N.Krot,³N.T.Kita,⁴E.S.Bullock,²K.Nagashima,^3,5T.Ushikubo,^1,6M.A.Ivanova
Geochimica et Cosmochimica Acta (in Press) lIk to Article [https://doi.org/10.1016/j.gca.2021.12.033]
¹Dept. of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, DC, USA 20560
²Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
³WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706
⁴Carnegie Institution for Science, Earth and Planets Laboratory, 5241 Broad Branch Rd., N.W., Washington, DC 20015, USA
⁵Kochi Institute for Core Sample Research, JAMSTEC, Nankoku, Kochi 783-8502, Japan
⁶Vernadsky Institute, Kosygin St. 19, Moscow, Russia
Copyright Elsevier

Five Type A CAIs from three CV3 chondrites (Vigarano, Northwest Africa 3118, Allende), which differ in age by no more than ∼10⁵ years, show mineralogical and textural evidence of gradual transition into Type Bs, indicating that Type B inclusions formed by evolution of Type A CAIs in the solar nebula. This model differs from the conventional condensation model in which aggregates of condensate grains form different kinds of CAIs depending on the relative populations of different kinds of grains. In our model the pyroxene forms nearly isochemically by reaction of perovskite with melilite under highly reducing conditions, and the reaction may be triggered by influx of hydrogen from the gas. Anorthite requires the addition of silica from the gas, and originally forms as veins and reaction rims on gehlenitic melilite within Fluffy Type As. Later partial re-melting of these assemblages results in the formation of poikilitic pyroxene and anorthite that enclose rounded (partially melted) tablets of melilite. Oxygen isotopes in four of the CAIs support the formation of Ti-rich ¹⁶O-depleted pyroxene from ¹⁶O-depleted perovskite, but not in the fifth CAI. An alternative possibility is that Ti-rich ¹⁶O-depleted pyroxene is the result of later solid-state exchange that preferentially affects the most Ti-rich pyroxene. Regardless of the origin of the ¹⁶O-depleted pyroxene, we give a model for nebular reservoir evolution based on sporadic FU-Orionis flare-ups in which the ¹⁶O-rich region near the proto-Sun fluctuated in size depending on whether the proto-Sun was in flare-up stage or quiescent.

¹Junya MATSUNO,^1,2,3Akira TSUCHIYAMA,⁴Akira MIYAKE,⁵Keiko NAKAMURA-MESSENGER,^5,6Scott MESSENGER
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.12.031]
¹Research Organization of Science and Technology, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga, 525-7, Japan
²CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou 510640, China
³CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China
⁴Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo, Kyoto 606-8502, Japan
⁵Johnson Space Center, NASA, Houston, TX 77058, United States
⁶Present address: Blue 22 Software, Houston, TX
Copyright Elsevier

GEMS (Glass with Embedded Metal and Sulfides) grains found in interplanetary dust particles are considered one of the most primitive materials in the Solar System, yet questions remain on how they formed. It has been suggested that GEMS grains are products of radiation processing and amorphization of sulfide and silicate mineral grains in the interstellar medium. Alternatively, GEMS grains are proposed to be disequilibrium condensation products in late-stage protosolar disks. We examined the 3D distributions of elements and inclusions within GEMS grains using TEM (transmission electron microscopic)-tomography to better constrain their possible formation processes. We found some core-shell particles composed of metals and amorphous silicates and observed a binary distribution of Mg/Si in amorphous silicates of GEMS grains. These properties are highly similar to the features of experimental condensation products. Furthermore, the location of sulfides only on the surface of GEMS and their larger sizes than metals are also consistent with the condensation experiments, where sulfides formed by sulfidation of metal grains with S-bearing gas species. Textures showing aggregation and possible coalescence of primary grains were also observed. Therefore, we conclude that GEMS grains are condensates from gas at high temperatures and some of them were aggregated.

¹Mehmet Yesiltas,²Thimothy D. Glotch,^3,4Melike Kaya
ACS Earth and Space Chemistry 5, 3281-3296 Link to Article [https://doi.org/10.1021/acsearthspacechem.1c00290]
¹Faculty of Aeronautics and Space Sciences, Kirklareli University, Kirklareli 39100, Turkey
²Department of Geosciences, Stony Brook University, Stony Brook, New York 11794, United States
³Institute of Acceleration Technologies, Ankara University, Ankara 06830, Turkey
⁴Turkish Accelerator and Radiation Laboratory (TARLA), Ankara 06830, Turkey

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2Jon M. Friedrich,¹Matthiew M. Chen,¹Stephanie A. Giordano,¹Olivia K. Matalka,¹Juliette W. Strasser,¹Kirstin A. Tamucci,³Mark L. Rivers,^2,4,5Denton S. Ebel
Microscopy Research & Technique (in Press) Link to Article [https://doi.org/10.1002/jemt.24043]
¹Department of Chemistry, Fordham University, Bronx, New York, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
³Center for Advanced Radiation Sources, University of Chicago, Argonne, Illinois, USA
⁴Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA
⁵Graduate Center of the City University of New York, New York, New York, USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Shigeko Togashi,¹Akihiko Tomiya,²Noriko T.Kita,^1,3Yuichi Morishita
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.12.029]
¹Geological Survey of Japan, AIST, Central 7, Higashi 1-1-1, Tsukuba 305-8567, Japan
²Department of Geoscience, University of Wisconsin, Madison 1215 W. Dayton Street Madison, WI 53706-1692, USA
³Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
Copyright Elsevier

The origin of the KREEP (K, Rare Earth Element and P)-rich component of the Mg-suite rocks of the Procellarum KREEP Terrane (PKT), one of three major lunar crustal terranes, is unclear. In an attempt to determine its origin, we estimated the composition of host magmas of plutonic rocks, including Mg-suite rocks and evolved rocks, from the PKT (PKT-host magmas) by using secondary ion mass spectrometry analyses of plagioclase. Calculated partition coefficients for Sr, Ba and Ti between plagioclase and melts, taking into account the anorthite content of plagioclase, temperature and bulk rock major-element compositions, were applied to determine parental magma compositions. The PKT-host magmas contained 160–360 ppm Sr, 520–7600 ppm Ba and 1.1–7.0 wt.% TiO2; most of them had higher Ti and Ba concentrations than KREEP basalts and high-K KREEP. We used phase relations based on the Rhyolite-MELTS algorithm to explore the evolution of the PKT-host magmas and KREEP basalts from two bulk silicate moon (BSM) starting compositions, a BSM with chondritic ratios of refractory elements, and a crustal-component-enriched BSM with non-chondritic ratios of refractory elements. We propose a three-stage evolution model. Stage-1: polybaric multi-step fractionation from a BSM magma to form ferroan anorthosite (FAN) crust and an evolved magma as the first KREEP-rich component (M0). Stage-2: assimilation and fractional crystallization (AFC) of M0, early cumulate and FAN associated with deep mantle overturn and impact events to form the PKT-host magmas, Mg-suite rocks and an evolved magma as the second KREEP-rich component (K0). Stage-3: further AFC cycles of K0, Mg-suite rocks or FAN associated with shallow mantle overturn and impact events to form KREEP basalts. This three-stage model for a crustal-component-enriched BSM with non-chondritic ratios of refractory elements (e.g., a sub-chondritic Ti/Ba ratio) reproduced the compositions of both the host magmas of FAN and the PKT-host magmas that fractionated to form the Mg-suite rocks and KREEP basalts of the PKT region. In particular, the model reproduced the high Ti and Ba contents of the PKT-host magmas we estimated from plagioclase composition. Variations of TiO2 and Ba contents (and hence Ti/Ba ratios) of the magmas were critical controls on their evolution.

¹François Robert,²Marc Chaussidon,²Adriana Gonzalez-Cano,¹Smail Mostefaoui
Proceeding sof the National Academy of Sciences of the United States of America (in Press) Link to Article [https://doi.org/10.1073/pnas.2114221118]
¹Institut Origine et Evolution, Muséum National d’Histoire Naturelle, Sorbonne Université, IMPMC-UMR 7590 CNRS, 75005 Paris, France;
²Université de Paris, Institut de Physique du Globe de Paris, CNRS, F-75005 Paris, France

Enrichment or depletion ranging from −40 to +100% in the major isotopes ¹⁶O and ²⁴Mg were observed experimentally in solids condensed from carbonaceous plasma composed of CO₂/MgCl₂/Pentanol or N₂O/Pentanol for O and MgCl₂/Pentanol for Mg. In NanoSims imaging, isotope effects appear as micrometer-size hotspots embedded in a carbonaceous matrix showing no isotope fractionation. For Mg, these hotspots are localized in carbonaceous grains, which show positive and negative isotopic effects so that the whole grain has a standard isotope composition. For O, no specific structure was observed at hotspot locations. These results suggest that MIF (mass-independent fractionation) effects can be induced by chemical reactions taking place in plasma. The close agreement between the slopes of the linear correlations observed between δ²⁵Mg versus δ²⁶Mg and between δ¹⁷O versus δ¹⁸O and the slopes calculated using the empirical MIF factor η discovered in ozone [M. H. Thiemens, J. E. Heidenreich, III. Science 219, 1073–1075; C. Janssen, J. Guenther, K. Mauersberger, D. Krankowsky. Phys. Chem. Chem. Phys. 3, 4718–4721] attests to the ubiquity of this process. Although the chemical reactants used in the present experiments cannot be directly transposed to the protosolar nebula, a similar MIF mechanism is proposed for oxygen isotopes: at high temperature, at the surface of grains, a mass-independent isotope exchange could have taken place between condensing oxides and oxygen atoms originated form the dissociation of CO or H₂O gas.

¹Van T. H. Phan,¹Rolando Rebois,¹Pierre Beck,¹Eric Quirico,¹Lydie Bonal,²Takaaki Noguchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13773]
¹Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Université Grenoble Alpes/CNRS-INSU, UMR 5274, Grenoble, F-38041 France
²Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto, 606-8502 Japan
Published by arrangement with John Wiley & Sons

Meteorite matrices from primitive chondrites are an interplay of ingredients at the sub-µm scale, which requires analytical techniques with the nanometer spatial resolution to decipher the composition of individual components in their petrographic context. Infrared spectroscopy is an effective method that enables the probing of vibrations at the molecule atomic scale of organic and inorganic compounds but is often limited to a few micrometers in spatial resolution. To efficiently distinguish spectral signatures of the different constituents, we apply here nano-infrared spectroscopy (AFM-IR), based on the combination of infrared and atomic force microscopy, having a spatial resolution beyond the diffraction limits. Our study aims to characterize two chosen meteorite samples to investigate primitive material in terms of bulk chemistry (the CI chondrite Orgueil) and organic composition (the CR chondrite EET 92042). We confirm that this technique allows unmixing the IR signatures of organics and minerals to assess the variability of organic structure within these samples. We report an investigation of the impact of the widely used chemical HF/HCl (hydrogen fluoride/hydrochloric acid) extraction on the nature of refractory organics (insoluble organic matter [IOM]) and provide insights on the mineralogy of meteorite matrices from these two samples by comparing to reference (extra)terrestrial materials. These findings are discussed with a perspective toward understanding the impact of post-accretional aqueous alteration and thermal metamorphism on the composition of chondrites. Last, we highlight that the heterogeneity of organic matter within meteoritic materials extends down to the nanoscale, and by comparison with IOMs, oxygenated chemical groups are not affected by acid extractions.

^1,2Julia Semprich,^2,3Justin Filiberto,²Allan H. Treiman,¹Susanne P. Schwenzer
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13775]
¹AstrobiologyOU, School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
²Lunar and Planetary Institute, USRA, 3600 Bay Area Blvd, Houston, Texas, 77058 USA
³Astromaterials Research and Exploration Science (ARES) Division, XI3, NASA Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

Low-grade metamorphic hydrous minerals and carbonates occur in various settings on Mars and in Martian meteorites. We present constraints on the stability of prehnite, zeolites, serpentine, and carbonates by modeling the influence of H2O-CO2 fluids during low-grade metamorphism in the Martian crust using compositions of a Martian basalt and an ultramafic cumulate. In basaltic compositions with 5 wt% fluid, our models predict prehnite in less oxidized, CO2-poor conditions (≤0.44 mol kg−1 CO2) on warmer geotherms of 20 °C km−1. At fluid-saturated conditions, epidote and laumontite are replaced by quartz, calcite, chlorite, and muscovite. In ultramafic compositions with 5 wt% fluid, antigorite (serpentine) is stable at CO2-poor conditions of ≤0.33 mol kg−1, while talc forms at 0.05–0.56 mol kg−1 CO2. At fluid-saturated conditions, antigorite is replaced by talc and chlorite, and at higher X(CO2) by magnesite and quartz. Our models therefore suggest that prehnite, zeolites, and serpentine have formed in a CO2-poor environment on Mars implying that fluids during their formation either did not contain high amounts of CO2 or had degassed CO2. Carbonates and potentially talc would have formed in the presence of a CO2-bearing fluid and therefore at different alteration stages than for prehnite, zeolites, and serpentine either in the same hydrothermal event during which the fluid composition changed gradually due to cooling and precipitation or by separate and successive alteration events with fluids of different compositions.