¹Sota Arakawa,²Daiki Yamamoto,³Takayuki Ushikubo,⁴Hiroaki Kaneko,⁵Hidekazu Tanaka,¹Shigenobu Hirose,⁴Taishi Nakamoto
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115690]
¹Yokohama Institute for Earth Sciences, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
²Department of Earth and Planetary Sciences, Kyushu University, 744, Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
³Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe-otsu, Nankoku, Kochi, 783-8502, Japan
⁴Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8550, Japan
⁵Astronomical Institute, Graduate School of Science, Tohoku University, 6-3 Aramaki, Aoba-ku, Sendai, 980-8578, Japan
Copyright ELsevier

Oxygen isotope compositions of chondrules reflect the environment of chondrule formation and its spatial and temporal variations. Here, we present a theoretical model of oxygen isotope exchange reaction between molten silicate spherules and ambient water vapor with finite relative velocity. We found a new phenomenon, that is, mass-dependent fractionation caused by isotope exchange with ambient vapor moving with nonzero relative velocity. We also discussed the plausible condition for chondrule formation from the point of view of oxygen isotope compositions. Our findings indicate that the relative velocity between chondrules and ambient vapor would be lower than several 100ms−1 when chondrules crystallized.

^1,2,3M.D.Suttle et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.06.027]
¹Planetary Materials Group, Natural History Museum, Cromwell Road, London, SW7 5BD, UK]
²School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
³Dipartimento di Scienze della Terra, Università di Pisa, 56126 Pisa, Italy
Copyright Elsevier

We searched late Miocene sedimentary rocks in an attempt to recover fossil micrometeorites derived from the Veritas asteroid family. This study was motivated by the previous identification of a pronounced 3He peak (4-5x above background) within marine sediments with ages between ∼8.5-6.9 Ma ago (Montanari et al. 2017. GSA Bulletin, 129:1357-1376). We processed 118.9 kg of sediment from the Monte dei Corvi beach section (Italy), the global type-section for the Tortonian epoch (11.6-7.2 Ma). Samples were collected both before and within the 3He peak. Although a small number of iron-rich (I-type) fossil micrometeorites were recovered from each horizon studied (Ntotal = 20), there is no clear difference between the pre- and intra- 3He peak samples. All micrometeorites are compositionally similar, and three out of five horizons yielded similar abundances and particle sizes. Micrometeorites extracted from sediments at the base of the 3He peak were exclusively small (ø <75 µm), while micrometeorites extracted from sediments near the highest 3He values were relatively large (ø <270 µm). The recovered fossil micrometeorites are interpreted as samples of the background dust flux derived from metal-bearing chondritic asteroids. The presence of a 3He signature combined with the absence of fossil micrometeorites or extraterrestrial spinels (Boschi et al. 2019, Spec. Pap. Geol. Soc. Am. 542:383-391) unambiguously related to the Veritas event suggests that the Veritas family is composed of highly friable materials that rarely survive on the sea floor to become preserved in the geological record. Our data supports the existing hypothesis that the Veritas asteroid family is an aqueously altered carbonaceous chondrite parent body, one that contains minimal native metal grains or refractory Cr-spinels. The low yield of fossil micrometeorites at Monte dei Corvi is attributed to loss of particles by dissolution whilst they resided on the sea floor but also due to high sedimentation rates leading to dilution of the extraterrestrial dust flux at this site. As with other fossil micrometeorite collections (e.g. Cretaceous chalk [Suttle and Genge, EPSL, 476:132-142]) the I-type spherules have been altered since deposition. In most particles, both magnetite and wüstite remain intact but have been affected by solid state geochemical exchange, characterised by partial leaching of Ni, Co and Cr and implantation of Mn, Mg, Si and Al. In some particles Mn concentrations reach up to 16.6 wt.%. Conversely, in some micrometeorites wüstite has been partially dissolved, or even replaced by calcite or ankerite. Finally, we observe evidence for wüstite recrystallisation, forming a second generation of magnetite. This process is suggested to occur by oxidation during residence on the seafloor and has implications for the use of fossil I-type micrometeorites as a potential proxy for probing Earth’s upper atmospheric composition (oxidative capacity) in the geological past. However, solutions to the limitations of post-depositional recrystallisation are suggested. Fossil I-type spherules remain a potential tool for palaeo-climatic studies.

¹Jinia Sikdar, Harry Becker,²Jan A. Schuessler
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13990]
¹Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
²Earth Surface Geochemistry, GFZ German Research Centre for Geosciences, Potsdam, Germany
Published by arrangement with John Wiley & Sons

Silicon and iron isotope compositions of different physically separated components of enstatite chondrites (EC) were determined in this study to understand the role of nebular and planetary scale events in fractionating Si and Fe isotopes of the terrestrial planet-forming region. We found that the metal–sulfide nodules of EC are strongly enriched in light Si isotopes (δ30Si ≥ −5.61 ± 0.12‰, 2SD), whereas the δ30Si values of angular metal grains, magnetic, slightly magnetic, and non-magnetic fractions become progressively heavier, correlating with their Mg# (Mg/(Mg+Fe)). White mineral phases, composed primarily of SiO2 polymorphs, display the heaviest δ30Si of up to +0.23 ± 0.10‰. The data indicate a key role of metal–silicate partitioning on the Si isotope composition of EC. The overall lighter δ30Si of bulk EC compared to other planetary materials can be explained by the enrichment of light Si isotopes in EC metals along with the loss of isotopically heavier forsterite-rich silicates from the EC-forming region. In contrast to the large Si isotope heterogeneity, the average Fe isotope composition (δ56Fe) of EC components was found to vary from −0.30 ± 0.08‰ to +0.20 ± 0.04‰. A positive correlation between δ56Fe and Ni/S in the components suggests that the metals are enriched in heavy Fe isotopes whereas sulfides are the principal hosts of light Fe isotopes in the non-magnetic fractions of EC. Our combined Si and Fe isotope data in different EC components reflect an inverse correlation between δ30Si and δ56Fe, which illustrates that partitioning of Si and Fe among metal, silicate, and sulfidic phases has significantly fractionated Si and Fe isotopes under reduced conditions. Such isotope partitioning must have occurred before the diverse components were mixed to form the EC parent body. Evaluation of diffusion coefficients of Si and Fe in the metal and non-metallic phases suggests that the Si isotope compositions of the silicate fractions of EC largely preserve information of their nebular processing. On the other hand, the Fe isotopes might have undergone partial or complete re-equilibration during parent body metamorphism. The relatively uniform δ56Fe among different types of bulk chondrites and the Earth, despite Fe isotope differences among their components, demonstrates that the chondrite parent bodies were not formed by random mixing of chondritic components from different locations in the disk. Instead, the chondrite components mostly originated in the same nebular reservoir and Si and Fe isotopes were fractionated either due to gas–solid interactions and associated changes in physicochemical environment of the nebular reservoir and/or during parent body processing. The heavier Si isotope composition of the bulk silicate Earth may require accretion of chondritic and/or isotopically heavier EC silicates along with cumulation of refractory forsterite-rich heavier silicates lost from the EC-forming region to form the silicate reservoir of the Earth.

^1,2,3,4Ryoga Maeda,¹Steven Goderis,⁵Akira Yamaguchi,⁶Thibaut Van Acker,⁶Frank Vanhaecke,²Vinciane Debaille,¹Phillippe Claeys
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14034]
¹Analytical-, Environmental-, and Geo-Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
²Laboratoire G-Time, Université libre de Bruxelles, Brussels, Belgium
³Submarine Resources Research Center (SRRC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
⁴REE Smelting Unit, Development of Production Technology for REE, General Project Team for SIP, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
⁵National Institute of Polar Research, Tokyo, Japan
⁶Atomic & Mass Spectrometry (A&MS) Research Unit, Department of Chemistry, Ghent University, Ghent, Belgium
Published by arrangement with John Wiley & Sons

The chemical effects of terrestrial alteration, with a particular focus on lithophile trace elements, were studied for a set of H chondrites displaying various degrees of weathering from fresh falls to altered finds collected from hot deserts. According to their trace element distributions, a considerable fraction of rare earth elements (REEs), Th, and U resides within cracks observed in weathered meteorite specimens. These cracks appear to accumulate unbound REEs locally accompanied by Th and U relative to the major element abundances, especially P and Si. The deposition of Ce is observed in cracks in the case of most of the weathered samples. Trace element maps visually confirm the accumulation of these elements in such cracks, as previously inferred based on chemical leaching experiments. Because the positive Ce anomalies and unbound REE depositions in cracks occur in all weathered samples studied here while none of such features are observed in less altered samples including falls (except for altered fall sample Nuevo Mercurio), these features are interpreted to have been caused by terrestrial weathering following chemical leaching. However, the overall effects on the bulk chemical composition remain limited as the data for all Antarctic meteorites studied in this work (except for heavily weathered sample A 09516, H6) are in good agreement with published data for unaltered meteorites.

¹Miriam Rüfenacht,¹Précillia Morino,^1,2Yi-Jen Lai,¹Manuela A. Fehr,^1,3Makiko K. Haba,¹Maria Schönbächler
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.06.005]
¹Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, CH-8092 Zurich, Switzerland
²Macquarie GeoAnalytical, Faculty of Science and Engineering, Macquarie University, Sydney, 2109, NSW, Australia
³Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ishikawadai Building 2-105, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan
Copyright Elsevier

Nucleosynthetic isotope variations are powerful tools to investigate genetic relationships between meteorite groups and planets. They are instrumental to assess the early evolution of the solar system, including mixing and reservoir formation in the protoplanetary disk, as well as planet formation. To address these questions, we report high-precision nucleosynthetic Ti isotope compositions of a wide range of bulk meteorites, partially complemented with new Cr isotope data. New Ti isotope data confirm the first order dichotomy observed between carbonaceous chondrites (CC), representing outer solar system compositions, and non-carbonaceous (NC) meteorites from the inner solar system. The data in combination with nucleosynthetic isotope data of other elements (e.g., Cr, Ca) indicate that isotopically heterogeneous reservoirs were also present as sub-reservoirs in the inner disk (NC reservoir), generating two or more clusters i.e., (i) the Vesta-like howardites-eucrites-diogenites (HEDs), mesosiderites, angrites, acapulcoites, lodranites, and brachinites and (ii) the Earth-Mars-like ordinary chondrites (OC), aubrites, enstatite chondrites (EC), winonaites, IAB silicates, rumuruti chondrites (R), Martian and terrestrial samples. These reservoirs likely represent disk substructures such as secondary gaps and ring-structures, created by spiral arms, which were emitted from the growing Jupiter and/or Saturn. The distinct isotopic compositions of these reservoirs may reflect thermal processing of material within the disk in combination with temporal isotopic variations either due to isotopically variable infalling material from a heterogeneous molecular cloud and/or thermal processing during the infall that induced such heterogeneities. Such effects were likely reinforced by thermal processing of the material within the disk itself and by physical size- and density sorting of dust caused by the giant planets, creating gaps and pressure bumps in the disk.

Genetic relationships of meteorite groups and their implications on parent body formation are evaluated. New high precision Ti isotope data are consistent with that (i) CH and CB meteorites derive from a common parent body, which most likely accreted material from the same isotopic reservoir as the parent body of CR chondrites, (ii) silicates of IAB irons and winonaites originate from the same parent body, and (iii) mesosiderites and HED meteorites have a common origin on Vesta. The indistinguishable Ti and Cr isotope compositions of HEDs/mesosiderites to acapulcoites are not attributed to a common parent body, because of petrologic and chemical differences in addition to their distinct O isotope compositions. Their parent bodies likely accreted in the same disk region, which showed a higher level of O isotope heterogeneity compared to that of Ti, Cr and other refractory nucleosynthetic tracers. The similarity in Ti isotope compositions of Martian meteorites and OCs indicates that OC-like material belongs to the main building blocks of Mars.

^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.