^1,2,3Xueping Yang,^1,2Zhixue Du,^1,2Yuan Li
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.06.017]
¹State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China
³College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Copyright Elsevier

Chlorine (Cl) is critical for Earth’s habitability and an important tracer for volatile accretion processes. Yet its chemical behavior during core formation, one of the major events throughout planetary formation, is still poorly understood. This is primarily hindered by experimental challenges of reproducing such extreme pressure and temperature conditions and characterizing chemical compositions of recovered samples. Here we perform experiments on Cl partitioning between iron-rich metallic melt (core analog) and silicate melt (mantle analog) at temperatures of 1900–2400 K and pressures of 1–18 gigapascals to simulate core-mantle differentiation of terrestrial planets. More importantly, to avoid likely complications of Cl loss due to wet or oil polishing, we find it is critical to apply dry polishing to recovered samples as shown in previous work focusing on halogens. Our determined partition coefficients of Cl between metallic melt and silicate melt range from <0.003 to 1.38, which shows its siderophile (iron-loving) behavior for the first time. Moreover, we find Cl gradually prefers metallic melt as the increase of pressure, while confirming a positive effect of oxygen contents in metallic liquid. Considering plausible core formation scenarios for Earth and Mars, our results indicate that Cl abundance in Mars’ mantle could be explained by a single-stage core formation scenario. While for the Cl budget in Earth’s mantle, multi-stage core formation with partial core-mantle equilibrium may be required, and this would provide further constraints for dynamics of core formation and volatile accretion.

^1,2Larry R. Nittler,^1,3Asmaa Boujibar,^4,5Ellen Crapster-Pregont,¹Elizabeth A. Frank,⁶Timothy J. McCoy,⁷Francis M. McCubbin,^8,9Richard D. Starr,^4,10Audrey Vorburger,^1,11Shoshana Z. Weider
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007691]
¹Earth and Planets Laboratory, Carnegie Institution of Washington, Washington, DC, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
³Geology Department, Department of Physics & Astronomy, Western Washington University, Bellingham, WA, USA
⁴Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY, USA
⁵Department of Earth and Environmental Sciences, Columbia University, New York, NY, USA
⁶National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
⁷Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX, USA
⁸Physics Department, The Catholic University of America, Washington, DC, USA
⁹Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
¹⁰Physics Institute, University of Bern, Bern, Switzerland
¹¹Agile Decision Services, Washington, DC, USA
Published by arrangement with John Wiley&Sons

Mercury, the innermost planet, formed under highly reduced conditions, based mainly on surface Fe, S, and Si abundances determined from MESSENGER mission data. The minor element Cr may serve as an independent oxybarometer, but only very limited Cr data have been previously reported for Mercury. We report Cr/Si abundances across Mercury’s surface based on MESSENGER X-Ray Spectrometer data throughout the spacecraft’s orbital mission. The heterogeneous Cr/Si ratio ranges from 0.0015 in the Caloris Basin to 0.0054 within the high-magnesium region, with an average southern hemisphere value of 0.0008 (corresponding to about 200 ppm Cr). Absolute Cr/Si values have systematic uncertainty of at least 30%, but relative variations are more robust. By combining experimental Cr partitioning data along with planetary differentiation modeling, we find that if Mercury formed with bulk chondritic Cr/Al, Cr must be present in the planet’s core and differentiation must have occurred at log fO₂ in the range of IW-6.5 to IW-2.5 in the absence of sulfides in its interior, and a range of IW-5.5 to IW-2 with an FeS layer at the core-mantle boundary. Models with large fractions of Mg-Ca-rich sulfides in Mercury’s interior are more compatible with moderately reducing conditions (IW-5.5 to IW-4) owing to the instability of Mg-Ca-rich sulfides at elevated fO₂. These results indicate that if Mercury differentiated at a log fO₂ lower than IW-5.5, the presence of sulfides whether in the form of a FeS layer at the top of the core or Mg-Ca-rich sulfides within the mantle would be unlikely.

^1,2Satu Hietala,³Jarkko Jokinen,¹Jouni Lerssi,¹Matti Niskanen,⁴Lauri J. Pesonen,²Jüri Plado
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14033]
¹Geological Survey of Finland, Kuopio, Finland
²Department of Geology, University of Tartu, Tartu, Estonia
³Loop and Line Oy, Kirkkonummi, Finland
⁴Solid Earth Geophysics Laboratory, Physics Department, University of Helsinki, Helsinki, Finland
Published by arrangement with John Wiley & Sons

The Summanen structure is located in Central Finland and is one of Finland’s 12 known meteorite impact structures. In 2017, the discovery of Summanen was based on numerous shatter cone boulders with planar deformation features (PDFs) and a circular electromagnetic anomaly, which is 2.6 km in diameter. The site was revisited in 2020 and 2022, and shatter cone-bearing outcrops were discovered. PDFs and feather features were identified in samples from these outcrops. A total of 38 PDF sets in 27 quartz grains resulted in rational crystallographic orientations concentrating on {101¯4}, {101¯3}, {101¯2}, and {112¯2}, implying shock pressures of 2–20 GPa. Gravity measurements were taken, and the electrical conductivity of the structure was studied. The gravimetric results revealed a circular negative anomaly of about 4 km in diameter, with an amplitude of −3.5 mGal. Excluding the gravitational effect of water and Quaternary sediments reduces the anomaly to −1.6 mGal. A bowl-shaped conductive layer, likely containing relict saline water in the impact-fractured bedrock, was identified to a depth of 240 m. Topographic and bathymetric data were combined to determine the impact’s effect and interpret the level of erosion. Cobbles of sedimentary sand- and siltstones were found on the coastline of Lake Summanen. Based on their similarity to those found in the Söderfjärden impact crater with a Cambrian age, it is likely that these rocks and post-impact infill are also of a similar age.

^1,2Noah Jäggi,²Antoine S. G. Roth,²Miriam Rüfenacht,²Maria Schönbächler,²André Galli
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14026]
¹Physikalisches Institut, University of Bern, Bern, Switzerland
²Institute für Geochemie und Petrologie, ETH Zürich, Zürich, Switzerland
Published by arrangement with John Wiley & Sons

Chondrules are microscopic, recrystallized melt droplets found in chondritic meteorites. High-resolution isotope analyses of minor elements require large enough element quantities which are obtained by dissolving entire chondrules. This work emphasizes the importance of X-ray computed tomography (XCT) to detect features that can significantly affect the bulk chondrule isotope composition. It thereby expands on other works by looking into chondrules from a wide range of chondrites including CR, CV, CB, CM, L, and EL samples before turning toward complex and time-consuming chemical processing. The features considered are metal and igneous rims, compound chondrules, matrix remnants, and metal contents. In addition to the identification of these features, computed tomography prevents the inclusion of non-chondrule samples (pure matrix or metal) as well as samples where two different chondrule fragments with potentially different isotope compositions are held together by matrix. Matrix surrounding chondrules is also easily detected and the affected chondrules can be omitted or reprocessed. The results strongly encourage to perform XCT before dissolution of chondrules for isotope analysis as a non-invasive method.

^1,2S. K. Bell,¹K. H. Joy,¹J. F. Pernet-Fisher,¹M. E. Hartley
Meteoritics & Planetary Science Open Access Link to Article [https://doi.org/10.1111/maps.14032]
¹Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK
²Rocktype Ltd, Magdalen Centre, Oxford, UK
Published by arrangement with John Wiley & Sons

Mare basalts collected at the Apollo 15 landing site are classified as belonging to either the quartz-normative suite or the olivine-normative suite, based on differences in whole-rock major element chemistry. A wide range of textures are displayed within samples from both suites, which provide insight into eruption processes on the Moon. Here we use crystal size distribution (CSD) analysis and spatial distribution pattern (SDP) analysis of pyroxene, olivine, and plagioclase crystals in eight Apollo 15 mare basalt samples to investigate the crystallization and emplacement of the quartz-normative and olivine-normative suites. In general, our results show similarities between the CSDs and SDPs for both mare basalt suites. However, we also report two distinct groups of pyroxene CSD trends that likely represent samples with common cooling histories, originating from comparable depths within respective olivine-normative and quartz-normative lava flows. We use our results to determine the relative depths of samples within the lava flows at the Apollo 15 landing site.

¹A. Deanne Rogers,²Steven W. Ruff,³Michael D. Smith
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115687]
¹Stony Brook University, Stony Brook, NY, USA
²Arizona State University, Tempe, AZ, USA
³NASA Goddard Space Flight Center, Greenbelt, MD, USA
Copyright Elsevier

It has been hypothesized that the dust component of the Martian surface is globally homogeneous, based on chemical similarity between landing sites and spectral similarity from select areas within bright regions. We tested that hypothesis by producing the first near-global data set of surface spectral emissivity (excluding polar regions) across the ~233–508 and 825–1650 cm−1 (~20–50 and 6–12 μm) spectral ranges from Mars Global Surveyor Thermal Emission Spectrometer data and using various data reduction techniques to search for any spectral heterogeneity in bright regions that might be present. We found no unequivocal evidence for spectral heterogeneity, supporting the hypothesis that dust is globally homogenized. The global emissivity product permits new spectral parameter maps and preliminary assessments of atmosphere-regolith interactions. We produced the first map of the Christiansen feature (CF) and show that, unlike on the Moon, where CF is a proxy for bulk silica content, CF position on Mars is primarily associated with dust cover. We produced an updated map of the 1630 cm−1 emissivity peak that arises from bound H2O in fine-particulate material and show that the peak is nearly ubiquitous across the Martian surface, including in dark regions with relatively low dust cover. This is attributed to minor amounts of dust disproportionally contributing to the spectral signal in the ~1630 cm−1 region. We show that regions within the equatorial dust deposits with higher annual modeled frequency of nighttime CO2 frosts are more likely to have lower emissivity in the ~1350-1400 cm−1 region, consistent with a higher fraction of unconsolidated dust. This provides the first spectral evidence for a previously hypothesized regolith gardening process via a diurnal CO2 cycle, representing an important surface-atmosphere interaction that may contribute to near-surface porosity and affect diffusive exchange of H2O between atmosphere and hydrated solids (ice, minerals) in the regolith.

¹Yevgeniy P. Gurov,¹Vitaliy V. Permiakov
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13999]
¹Institute of Geological Sciences, National Academy of Sciences of Ukraine, Kyiv, Ukraine
Published by arrangement with John Wiley & Sons

Metallic microspheres have been found in rocks from the Onaping Formation of the Sudbury impact structure, Canada. Microspherules are common in contact breccias, the lowest part of the Dowling Member, and rare microspherules have been found in the upper sequences of the Dowling Member. Separate microspherules are dispersed in the breccia matrix and do not form clusters. The sizes of the microspheres range from 5 to 30 μm; most commonly, they are 8–15 μm in size. The microspherules have a regular spherical shape, and in some cases show concentric zonal structures. The microspherules consist mostly of the refractory elements Cr, Co, Fe, Mo, W, and Ti, with a predominant Ni content of 40–75 wt%. The formation of the Sudbury metal microspherules by condensation in a high-temperature plume is suggested by their spherical shape, concentric-zoned structure, uniform composition, and distribution in fallback breccias of the crater-fill Onaping Formation. The content of the most refractory W in the composition of the microspheres indicates early condensation. A decrease in the content of W and an increase in the content of Ni in the microspheres of the upper layers relative to the content of these elements in the earliest microspheres of the contact layers indicate that they could have formed by fractional condensation during the expansion and cooling of the impact vapor plume. As source material, a combination of target rocks with high nickel content with a chondritic impactor is suggested.

¹Naotaka Tomioka et al. (>10)
Nature Astronomy 7, 669–677 Open Access Link to Article [DOI https://doi.org/10.1038/s41550-023-01947-5]
¹Kochi Institute for Core Sample Research, X-star, Japan Agency for Marine-Earth Science and Technology, Nankoku, Japan

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

¹Alexander Rogaski,^1,2Gokce K. Ustunisik,³Shuying Yang,³Munir Humayun,⁴Kevin Righter,⁵Jeff A. Berger,⁶Nicholas DiFrancesco
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14000]
¹Department of Geology and Geological Engineering, South Dakota School of Mines and Technology, Rapid City, South Dakota, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
³National High Magnetic Field Laboratory, Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, Florida, USA
⁴National Aeronautics and Space Administration, Lyndon B. Johnson Space Center, Houston, Texas, USA
⁵Jacobs JETSII, NASA Johnson Space Center, Houston, Texas, USA
⁶Department of Geology, University at Buffalo, Buffalo, New York, USA
Published by arrangement with John Wiley & Sons

The surface of Mars is enriched in Cl and S which is linked to volcanic activity and degassing. Similarly, elevated Ge and Zn levels in Gale crater sedimentary bedrock indicate a magmatic source for these elements. To constrain the relative effects of Cl and S on the outgassing of these trace metals and chemical characteristics of primary magmatic vapor deposits incorporated to Martian surface, we conducted a set of degassing and fumarolic alteration experiments. Ge is found to be more volatile than Zn in all experiments. In S-bearing runs, the loss of Ge and Zn was less than any other experiments. In Cl-only runs, degassing of Zn was more than twice that of Ge within the first 10 min and percent loss increased for both elements with increasing time. In Cl + S runs, S-induced reduction of GeO2 and ZnO to metallic Ge and Zn switches the preference of chloride formation from Zn to Ge. Up to 90% of Ge and Zn loss in the 1-h no volatile-added (NVA) experiments might be due to the small amounts of Cl contamination in NVA mixes via other oxides used for synthesis. Alteration experiments show different phases between 1-h and 24-/72-h runs. In 1-h runs, anhydrite and langbeinite dominate while in 24-/72-h runs halite and sylvite dominate the condensate assemblages. S-bearing phases form as the intermediate products of fumarolic deposition, while chlorides are common when the system is allowed to cool gradually. One-hour exposure was sufficient to form alteration phases and vapor deposits such as NaCl, KCl, CaSO4, and langbeinites on the Martian analog minerals. These salts were identified in Martian meteorites and in situ measurements. Our results provide evidence that volcanic degassing along with fumarolic alteration could be a potential source for the enrichment and varying abundances of Cl, S, Fe, Zn, Ge in Martian surface, as well as a cause for Ge depletion in shergottites.

¹K.E. Bristol,^1,2A.V. Smirnov,³E.J. Piispa,⁴M.R. Ramirez Navas,⁵A. Kosterov,^6,7E.V. Kulakov
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115684]
¹Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI, USA
²Department of Physics, Michigan Technological University, Houghton, MI, USA
³Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland
⁴Instituto Geografico Militar, Quito, Ecuador
⁵Department of Earth Physics, Saint Petersburg University, Saint Petersburg, Russia
⁶Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Norway
⁷Northland Pioneer College, Show Low, AZ, USA
Copyright Elsevier

We investigated the magnetic properties of Ecuador’s first reported meteorite fall (March 23, 2008), the Daule ordinary chondrite (L5, S4, W0) using thermomagnetic analyses at high and cryogenic temperatures, analyses of magnetic hysteresis and first-order reversal curves, and thermal and alternating field (AF) demagnetization of natural remanent magnetization (NRM). The mineralogical and chemical composition of Daule was examined using scanning electron microscopy with energy-dispersive x-ray spectroscopy. Most methods indicate that the magnetic properties of Daule are dominated by multidomain FeNi alloys (kamacite) with Ni content varying between ~4% and ~ 17%. However, backfield demagnetization (BFD) analyses revealed the presence of high-coercivity tetrataenite that survived shock metamorphism. The differential survival of tetrataenite at the millimeter scale indicates heterogeneity of the impact-related temperature and pressure fields within the Daule meteorite. BFD curves may serve as an efficient tool for identifying minor amounts of tetrataenite that otherwise cannot be discerned from the signal from magnetically-soft FeNi mineral phases by methods based on induced magnetization. Thermal demagnetization experiments unveiled the presence of a well-defined characteristic component of NRM, which remains resistant to AF demagnetization. We interpret this component as a pre-impact thermochemical remanence carried by tetrataenite and acquired during the thermal metamorphism of the parent body. At cryogenic temperatures, the magnetic properties of Daule are dominated by low-Mg magnesiochromite with the Curie temperature at 60–70 K.