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.

^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.

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.

¹David J. Lawrence,¹Patrick N. Peplowski,¹Jack T. Wilson,²Richard C. Elphic
Journal of Geophysical research (Planets) (in Press) Open Access Link to Article [https://doi.org/10.1029/2022JE007197]
¹Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, United States
²NASA Ames Spaceflight Center, Moffett Field, California, United States
Published by arrangement with John Wiley & Sons

A global map of bulk hydrogen abundances on the Moon is presented. This map was generated using data from the Lunar Prospector Neutron Spectrometer. This map required corrections for variations due to rare-earth elements, and was calibrated to Apollo sample hydrogen abundances. Since neutron-derived measurements sample hydrogen content to a depth of tens of cm, these results provide complementary insights to those provided by studies using spectral reflectance data, which sample depths of order μm. Comparison of these abundances to Apollo sample values suggest that the samples reflect actual hydrogen content on the lunar surface, not dominantly from non-lunar contamination. The average lunar hydrogen abundance is 47 ppm with a systematic uncertainty of ∼10 ppm. This is consistent with bulk hydrogen from solar wind emplacement. A bulk hydrogen enhancement (50–68 ppm) has been identified at the Moon’s largest pyroclastic deposit (Aristarchus Plateau), which corroborates prior observations that hydrogen and/or water plays a role in lunar magmatic events. Global data show a correlation between hydrogen and evolved materials rich in incompatible trace elements (i.e., KREEP type rocks), with a hydrogen excess of 14–36 ppm in these materials. Based on this hydrogen enhancement, we estimate a lower-limit water abundance within urKREEP materials (i.e., the final ∼2% of the lunar magma ocean) of 320–820 ppm H2O. This observation implies that water played a role in the original magma-ocean formation and solidification with a lower-limit water content in the original lunar magma ocean of 7–16 ppm or higher.

¹D. Halbert,¹J. Parnell
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13829]
¹School of Geosciences, University of Aberdeen, King’s College, Meston Building, Aberdeen, AB24 3UE UK
Published by arrangement with John Wiley & Sons

Thermal conductivity of natural rock is only well characterized for temperatures above 273 K, i.e., at typical Earth values. In planetary science, there is a requirement to explore the thermal characteristics of rock at temperatures below 273 K, for which thermal conductivity data are sparse or contested. Here, we present empirical data for a basalt showing thermal conductivity ranging from 2.71 ± 0.09 W m−1 K−1 at 224.4 K, to 2.63 ± 0.05 W m−1 K−1 at 288.8 K. Previous work reports much lower values in this range, which may be due to the fragmented nature of the previous research, the use of powdered samples for some data, and the effect of porosity. The high-temperature thermal conductivity laws of Sass et al. (1992) and Haenel and Zoth (1973) can be robustly extrapolated to cover the temperature range of our data.

¹Amber Zandanel,¹Roland Hellmann,¹Laurent Truche,²Vladimir Roddatis,³Michel Mermoux,⁴Gaël Choblet,⁴Gabriel Tobie
Nature Astronomy 6, 554-559 Link to Article [DOI https://doi.org/10.1038/s41550-022-01613-2]
¹Université Grenoble Alpes, CNRS, ISTerre, Grenoble, France
²GFZ German Research Centre for Geosciences, Potsdam, Germany
³Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France
⁴Nantes Université, Université Angers, Le Mans Université, CNRS, UMR 6112, Laboratoire de Planétologie et Géosciences, Nantes, France

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^1,2Di-Sheng Zhou,^1,2Xiao-Wen Yu,^2,3Rui Chang,^1,4,5Yu-Yan Sara Zhao,^1,4Xiongyao Li,^1,4Jianzhong Liu,³Honglei Lin,^3,6Chao Qi
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007202]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
²University of Chinese Academy of Sciences, Beijing, China
³Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
⁴CAS Center for Excellence in Comparative Planetology, Hefei, China
⁵International Center for Planetary Science, College of Geosciences, Chengdu University of Technology, Chengdu, China
⁶College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

The dissolution rates of jarosite can constrain the duration of aqueous activities on Mars. To date, few studies have considered the influences of formation pathways and anion substitutions on jarosite dissolution rates. Here, we investigated how the formation pathways (Fe(II)-oxidation and Fe(III)-forced hydrolysis) and incorporation of bromide influence the dissolution rates of K-jarosite under eight aqueous conditions combining T (277 K, 298 K, and 323 K) and αw (0.35, 0.75 and 1), except for 277 K−0.35αw. The results show that jarosite dissolution rates are primarily influenced by aqueous T-αw conditions. Formation pathways and Br contents are secondary factors and only become notable under low T (277 K) and low αw (0.35) conditions. Taking the jarosite formation pathways and Br incorporation into account, the maximum lifetime of jarosite may be slightly longer than that of the halogen-free counterparts formed via Fe(III)-forced hydrolysis. Jarosite of the Burns Formation (Meridiani Planum) and the Pahrump Hills member (Gale Crater) are likely formed via Fe(II)-oxidation and halogen-bearing. Their estimated field lifetime (∼150 μm–1 mm particles) in low-T groundwater may last for hundreds of thousand years to a few million years. Jarosite in the Vera Rubin Ridge would share a similar lifespan if low-T solutions account for jarosite formation and subsequent interactions; otherwise, interactions with hydrothermal fluids (∼100°C) would substantially shorten the jarosite lifetime. We conclude that Martian jarosite may survive continuous aqueous interactions for up to a few million years, indicating an extended duration of aqueous environments than previously thought.

^1,2Perello, J.F. et al. (>10)
Physical Review C 105, 035805 Link to Article [DOI 10.1103/PhysRevC.105.035805]
¹Department of Physics, Florida State University, Tallahassee, 32306, FL, United States
²Intelligence and Space Research Division, Los Alamos National Laboratory, Los Alamos, 87545, NM, United States

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¹Yobregat, Elsa,¹Fitoussi, Caroline,²Pili, Eric,¹Touboul, Mathieu
International Journal of Mass Spectrometry 476, 116846 Link to Article [DOI 10.1016/j.ijms.2022.116846]
¹Laboratoire de Géologie de Lyon (LGL-TPE), CNRS UMR 5276, Univ. Lyon, UCBL, ENS de Lyon, 46 allée d’Italie, 69364, Lyon Cedex 7, France
²CEA, DAM, DIF, Arpajon, F-91297, France

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¹C.J.Renggli,¹S.Klemme,²A.Morlok,¹J.Berndt,²I.Weber,²H.Hiesinger,³P.L.King
Earth and Planetary Science Letters 593, 117647 Link to Article [https://doi.org/10.1016/j.epsl.2022.117647]
¹Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Münster, 48149, Germany
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Münster, 48149, Germany
³Research School of Earth Sciences, The Australian National University, Canberra, 2601, Australia
Copyright Elsevier

The surface of Mercury is enriched in sulfur, with up to 4 wt.% detected by the NASA MESSENGER mission, and has been challenging to understand in the context of other terrestrial planets. We posit, that magmatic S was mobilized as a gas phase in volcanic and impact processes near the surface, exposing silicates to a hot S-rich gas at reducing conditions and allowing conditions for rapid gas-solid reactions. Here, we present novel experiments on the reaction of Mercury composition glasses with reduced S-rich gas, forming Ca- and Mg-sulfides. The reaction products provide porous and fragile materials that create previously enigmatic hollows on Mercury. Our model predicts that the gas-solid reaction forms Ca-Mg-Fe-Ti-sulfide assemblages with SiO2 and aluminosilicates, distinct from formation as magmatic minerals. The ESA/JAXA BepiColombo mission to Mercury will allow this hypothesis to be tested.