Tarunika Ramprasad¹, Pierre Haenecour², Kenneth Dominik², Thomas J. Zega^1,2
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13910]
¹Department of Materials Science and Engineering, University of Arizona, 1235 E. James E. Rogers Way, Tucson, Arizona
²Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson, Arizona 85721, USA
85721, USA
Published by arrangement with John Wiley & Sons

Compact type A calcium-aluminum-rich inclusions (CTA CAIs) are believed to have experienced partial melting that erased all information on their original nebular condensation. To investigate this question, we report new microstructural data on a CTA CAI, composed primarily of melilite, spinel, and perovskite, in the Northwest Africa 5028 CR2 chondrite. The melilite grains contain low (5–10 mole%) åkermanite contents and are not compositionally zoned. Spinel and perovskite each occur as near endmember compositions MgAl₂O₄ and CaTiO₃ and contain minor V and Al, respectively. A continuous rim composed of melilite, spinel, and perovskite, with minor hibonite grains occur around the CAI. We extracted two regions of interest from the interior CAI and two from the rim using focused ion beam techniques for detailed analysis using transmission electron microscopy. Evidence for thermal processing occurs as a perovskite–spinel–spinel triple junction in an interior section and a spinel inclusion within perovskite in a rim section. Evidence for parent-body alteration occurs in the form of Fe-rich sheet silicates in the rim, and localized amstallite in the interior of the CAI. While previous work suggested that many CTA CAIs experienced thermal processing in the solar nebula, including partial melting, our data show that signatures of primary condensation can be preserved in the form of more refractory phases contained within less refractory minerals, namely melilite and perovskite grains within spinel, and hibonite grains within perovskite, respectively. The inclusion we report on here has a complex history involving gas-phase condensation, nebular thermal processing, and parent-body alteration.

Dilyara M. Kuzina¹, Jérôme Gattacceca², Natalia S. Bezaeva³, Dmitry D. Badyukov³, Pierre Rochette², Yoann Quesnel², François Demory², Daniel Borschneck²
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13906]
¹Institute of Geology and Petroleum Technologies, Kazan Federal University, 4/5 Kremlyovskaya Str, 420008 Kazan, Russia ²CNRS, Aix Marseille Univ, IRD, INRAE, Aix-en-Provence, France
³Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19 Kosygin Str, 119991 Moscow, Russia
Published by arrangement with John Wiley & Sons

We present a paleomagnetic study of the ~10 km diameter Karla impact structure in Russia. We sampled the target carbonate rocks, and a yet undocumented fragmental melt-bearing lithic breccia layer. This impact breccia, which contains carbonate melt, is enriched in stoichiometric magnetite by a factor of ~15 compared to the target lithologies, and carries a stable natural remanent magnetization. The weak remanent magnetization and the presence of both normal and reverse polarities down to the centimeter scale indicate that the breccia does not carry a thermoremanent magnetization (TRM), but rather a chemical remanent magnetization (CRM). The presence of stoichiometric magnetite and the absence of TRM suggest that the magnetite was formed during relatively low-temperature postimpact hydrothermalism that affected the porous impact breccia layer. During this process, the breccia acquired a CRM. The paleomagnetic direction is compatible with a Cenozoic age for the impact event, but cannot bring more precise constraint on the age because of the stable position of the Eurasian plate over the last 60 Myr. However, the presence of both polarities indicates that mild hydrothermalism took place over a period of time long enough to span at least one reversal of the geomagnetic field, that is, over a time scale of the order of 100 kyr. This confirms that protracted hydrothermal systems associated with impact craters are long lived, even in relatively small craters such as Karla, and are key features of the geologic and environmental effects of impacts on Earth.

Bidong Zhang¹, Nancz L. Chabot¹ and Alan E. Rubin¹
Science Advances – Link to Article [https://www.science.org/doi/full/10.1126/sciadv.abo5781]
¹Department of Earth, Planetary and Space Sciences, University California, Los Angeles, CA 90095-1567, USA.
²Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
Copyright Elsevier

The parent cores of iron meteorites belong to the earliest accreted bodies in the solar system. These cores formed in two isotopically distinct reservoirs: noncarbonaceous (NC) type and carbonaceous (CC) type in the inner and outer solar system, respectively. We measured elemental compositions of CC-iron groups and used fractional crystallization modeling to reconstruct the bulk compositions and crystallization processes of their parent asteroidal cores. We found generally lower S and higher P in CC-iron cores than in NC-iron cores and higher HSE (highly siderophile element) abundances in some CC-iron cores than in NC-iron cores. We suggest that the different HSE abundances among the CC-iron cores are related to the spatial distribution of refractory metal nugget–bearing calcium aluminum–rich inclusions (CAIs) in the protoplanetary disk. CAIs may have been transported to the outer solar system and distributed heterogeneously within the first million years of solar system history.

Marceau Lecasble, Laurent Remusat, Jean-Christophe Viennet, Boris Laurent, Sylvain Bernard
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.039]
Muséum National d’Histoire Naturelle, Sorbonne Université, CNRS UMR 7590, IMPMC, Paris, France
Copyright Elsevier

Carbonaceous chondrites contain a diverse suite of more or less soluble compounds, including polycyclic aromatic hydrocarbons (PAHs). These compounds are structured around two or more fused benzene rings, and have shown to be detected in various astrophysical environments. The origin of PAHs in carbonaceous chondrites is debated: they may originate from the interstellar medium (ISM) and thus potentially carry information on accretion processes. Alternatively, they may have formed or transformed during secondary processes on parent bodies and thus carry information about aqueous alteration conditions. Here, we investigate the nature, quantity, and isotopic composition of free PAHs in three recently recovered CM chondrites having experienced substantial and distinct degrees of alteration: the CM2.2 Aguas Zarcas, the CM2.0 Mukundpura and the CM1/2 Kolang. All the CMs investigated contain PAHs, with sizes ranging from 2 (naphthalene) to 5 cycles (benzopyrene). The concentration of PAHs is not correlated to the degree of alteration and larger PAHs are also the most depleted in ¹³C, suggesting an interstellar origin. Yet, the abundance of alkylated PAHs appears correlated to the degree of alteration and all the extracted PAHs are D-depleted, pointing towards hydrogen exchange with water having occurred during aqueous alteration. These combined results suggest that PAHs in CCs likely carry information on both accretion and alteration processes.

David W. Graham, Kevin Konrad¹
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.09.016]
College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331 USA
Copyright Elsevier

We report ³He and ⁴He concentrations in 57 sediment samples from the southeast Indian Ocean where ⁶⁰Fe excesses were previously identified in a subset of the same samples (Wallner et al., 2016). The coupled ⁶⁰Fe-³He data allow further evaluation of two competing hypotheses: 1) a nearby supernova (SN) showered Earth with exotic radionuclides such as ⁶⁰Fe during the last 3 million years, or 2) ⁶⁰Fe in terrestrial archives was generated by reactions of galactic cosmic rays (GCRs) on micrometeorite grains that were irradiated for hundreds of millions of years in the interstellar medium, where ³He production by GCRs is larger than the solar wind ³He flux.

^aKeqing Zong et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.037]
¹State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
Copyright Elsevier

Lunar soil is a fine mixture of local rocks and exotic components. The bulk-rock chemical composition of the newly returned Chang’E-5 (CE-5) lunar soil was studied to understand its chemical homogeneity, exotic additions, and origin of landing site basalts. Concentrations of 48 major and trace elements, including many low-concentration volatile and siderophile elements, of two batches of the scooped CE-5 soil samples were simultaneously obtained by inductively coupled plasma mass spectrometry (ICP-MS) with minimal sample consumption. Their major and trace elemental compositions (except for Ni) are uniform at milligram levels (2–4 mg), matching measured compositions of basaltic glasses and estimates based on mineral modal abundances of basaltic fragments. This result indicates that the exotic highland and KREEP (K, rare earth elements, and P-rich) materials are very low (<5%) and the bulk chemical composition (except for Ni) of the CE-5 soil can be used to represent the underlying mare basalt. The elevated Ni concentrations reflect the addition of about 1 wt% meteoritic materials, which would not influence the other bulk composition except for some highly siderophile trace elements such as Ir. The CE-5 soil, which is overall the same as the underlying basalt in composition, displays low Mg# (34), high FeO (22.7 wt%), intermediate TiO₂ (5.12 wt%), and high Th (5.14 µg/g) concentrations. The composition is distinct from basalts and soils returned by the Apollo and Luna missions, however, the depletion of volatile or siderophile elements such as K, Rb, Mo, and W in their mantle sources is comparable. The incompatible lithophile trace element concentrations (e.g., Ba, Rb, Th, U, Nb, Ta, Zr, Hf, and REE) of the CE-5 basalts are moderately high and their pattern mimics high-K KREEP. The pattern of these trace elements with K, Th, U, Nb, and Ta anomalies of the CE-5 basalts cannot be explained by the partial melting and crystallization of olivine, pyroxene, and plagioclase. Thus, the mantle source of the CE-5 landing site mare basalt could have contained KREEP components, likely as trapped interstitial melts. To reconcile these observations with the initial unradiogenic Sr and radiogenic Nd isotopic compositions of the CE-5 basalts, clinopyroxene characterized by low Rb/Sr and high Sm/Nd ratios could be one of the main minerals in the KREEP-bearing mantle source. Consequently, we propose that the CE-5 landing site mare basalts very likely originated from partial melting of a shallow and clinopyroxene-rich (relative to olivine and orthopyroxene) upper mantle cumulate with a small fraction (about 1–1.5 %) of KREEP-like materials.

Tiantian Liu^a Kai Wünnemann^a,b GregMichael^a
Earth and Planetary Science Letters (in Press) Link to Article [https://doi.org/10.1016/j.epsl.2022.117817]
^aMuseum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, 10115 Berlin, Germany
^bFreie Universität Berlin, Malteserstr., 74-100, 12249 Berlin, Germany
Copyright: Elsevier

The early impact bombardment extensively fractured the lunar crust resulting in the formation of the so-called megaregolith. Previous estimates of megaregolith distribution vary significantly with respect to the vertical extent and the size-frequency distribution of fragments was rarely studied. We built a spatially resolved numerical model to simulate the process of cumulative impact fragmentation, aiming to backtrack the megaregolith evolution history and to constrain its fragment distribution. The results highlight the pivotal role of basin-forming events on the megaregolith formation. Especially the South-Pole Aitken (SPA) impact established the initial megaregolith structure which remained distinct after 0.5 Ga subsequent fragmentation. At 3.8 Ga, the megaregolith displays substantial lateral variation and layering: the highly fractured upper layer of ∼2.5 km is dominated by meter-scale fragments; the disturbed lower layer deeper than tens of kilometers is mainly consisting of kilometer-scale fragments; the transition zone >5 km contains fragments of various size scales.

¹L. M. Thompson,¹J. G. Spray,¹C. O’Connell-Cooper,²J. A. Berger,³A. Yen,⁴R. Gellert,⁴N. Boyd,⁴M. A. McCraig,⁵S. J. VanBommel
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007178]
¹Planetary and Space Science Centre, University of New Brunswick, Fredericton, Canada
²NASA Johnson Space Center, Houston, USA
³Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA
⁴Department of Physics, University of Guelph, Ontario, Canada
⁵Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, USA
Published by arrangement with John Wiley & Sons

Chemical data acquired by Curiosity’s Alpha Particle X-ray Spectrometer (APXS) during examination of the contact between the upper Mount Sharp group and overlying Stimson formation sandstones at the Greenheugh pediment reveal compositional similarities to rocks encountered earlier in the mission. Mount Sharp group strata encountered below the Basal Siccar Point group unconformity at the base and top of the section, separated by >300 m in elevation, have distinct and related compositions. This indicates enhanced post-depositional fluid flow and alteration focused along this contact. Sandstone targets exposed immediately above the unconformity have basaltic compositions consistent with previously encountered eolian Stimson formation sandstones, except at the contact, where they show the addition of S. Resistant sandstone outcrops above the contact have higher K, Mn and Na and lower Ni concentrations that primarily reflect changes in provenance. They are compositionally related to cap rock float blocks encountered as Curiosity climbed through the Mount Sharp group, and Bradbury group sandstone outcrops. The higher K, pediment sandstones are interpreted to have a similar provenance to some Bradbury group sandstones, further evidence for widespread, alkaline source rock within and/or in the vicinity of Gale crater. The Bradbury and Siccar Point groups may both be younger than the Mount Sharp group. Alternatively, an alkaline source area in and around Gale crater has been eroded by both water and wind at different times (both before and after deposition of the Mount Sharp group), during the evolution of the crater and its infill.

¹Levent Karacasulu,²David Karl,²Aleksander Gurlo,¹Cekdar Vakifahmetoglu
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115270]
¹Department of Materials Science and Engineering, Izmir Institute of Technology, Urla, 35430 Izmir, Turkey
²Technische Universitaet Berlin, Institute of Materials Science and Technology, Chair of Advanced Ceramic Materials, Straße des 17. Juni 135, 10623 Berlin, Germany
Copyright Elsevier

Mars regolith simulant (MGS-1) was densified for the first time via a cold sintering process (CSP) as a novel in-situ resource utilization (ISRU) concept. The technique comprises the utilization of NaOH solution as a liquid media during the densification of simulant powder with <100 μm particle size. In as short as 30 min, with the increase in the NaOH concentration (from 3 M to 10 M) and processing temperature (from 150 °C to 250 °C), the relative densities of the regolith compacts and the mechanical properties were enhanced. The artifacts produced with Mars regolith simulant powder at 250 °C using 10 M NaOH solution yielded a relative density of around 88% and compressive strength reaching ~45 MPa.

^1,2Brandon G. Radoman-Shaw,³Ralph P. Harvey,⁴Gustavo Costa,⁴Nathan S. Jacobson,⁵Amir Avishai,⁴Leah M. Nakley,⁴Daniel Vento
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13902]
¹Department of Mathematical, Physical, and Engineering Sciences, Texas A&M University – San Antonio, San Antonio, Texas, 78224 USA
²Department of Geography and Environmental Studies, Texas State University, San Marcos, Texas, 78666 USA
³Department of Earth, Environmental, and Planetary Science, Case Western Reserve University, Cleveland, Ohio, 44106 USA
⁴NASA Glenn Research Center, Cleveland, Ohio, 44135 USA
⁵Carl Zeiss SMT-PCS, Pleasanton, California, 94588 USA
Published by arrangement with John Wiley & Sons

Climate models for Venus rely heavily on theoretical modeling and laboratory experimentation due to the extreme surface conditions of the planet and limited in situ surface data. To better explore the relative importance of reactions between the surface and the atmosphere on Venus, we exposed representative volcanic glasses and basaltic minerals to a large-scale simulation of Venus surface conditions with a realistic atmospheric composition. This study consistend of two experiments of 42 and 80 days that replicated both physical conditions and atmosphere composition derived from available in situ near-surface data using the Glenn Extreme Environment Rig (GEER) at the NASA Glenn Research Center. These experiments revealed significant reactivity of common Ca-bearing pyroxenes (diopside and augite) to form anhydrite. Olivine and labradorite showed minimal reactivity. Volcanic glasses, including both natural and synthetic samples, were exceptionally reactive, rapidly forming both anhydrite and thénardite (Na2SO4), as well as transition metal sulfates (i.e., Cu, Cr), halite (NaCl), and sylvite (KCl). Our results document chemical and textural alteration of sample surfaces and provide sufficient evidence for an active sulfur sink on multiple samples, with sulfates as the dominant secondary mineralogy. These experiments suggest likely surface mineralogies and solid phases present on Venus’ surface with significant implications for upcoming missions and provide new data for comparison to high-temperature mineral–gas reactions prevalent on Venus, Earth, and Io.