¹PengYue Wang, ² Edward Cloutis, ¹Ye Su, ³PengFei Zhang
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116320]
¹State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
²Department of Geography, University of Winnipeg, Winnipeg, Canada
³Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
Copyright Elsevier

The establishment of robust meteorite-asteroid links has been a major focus of planetary exploration, and a major driver of asteroid sample return missions. Reflectance spectroscopy has been shown to be a powerful tool for this purpose. For the meteorites dominated by silicate minerals, quantitative analysis of spectral absorption features caused by the Fe2+-bearing minerals (mainly olivine and pyroxene) is a common method to determine mafic silicate mineralogy and end member abundances, and establish the relationship between them and possible parent bodies. In this study, the reflectance spectra of 22 primitive achondrites (acapulcoites, lodranites and winonaites) from NASA RELAB database were analyzed to determine their positions in the plot of the band area ratio (BAR) and 1 μm band center (Band I center). We found that Band I center and BAR of acapulcoites and lodranites are in roughly the same range. Acapulcoite-lodranite partially overlap with the field of H chondrites in the plot of the BAR and Band I center. This overlap means that spectral calibrations (also referred to as mineralogical formulas) based on the two types of meteorites needs to be applied with caution. The 2 μm band center of acapulcoite–lodranite is significantly lower than that of H chondrites, which is consistent with the conclusion of previous studies and provides a means to separate these two groups. In addition, the choice of spectral parameter analysis techniques may be a potential error source in similar studies. We provide generalized spectral fields of primitive achondrites in the plot of the BAR and Band I center derived from two widely used technologies.

^1,2,3Pierre-Marie Zanetta et al.  (>10)
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.09.021]
¹CNRS, Université Jean Monnet Saint-Étienne, ENS de Lyon, LGL-TPE, UMR5276, F-42023 Saint-Etienne, France
²Aix-Marseille Université, CNRS, IRD, INRAE, CEREGE, 13545 Aix-en-Provence, France
³Mineral Analysis Laboratory of SODEMI, 31, Bd des Martyrs, Abidjan-Cocody, 01 BP 2816, Abidjan 01, Cote d’Ivoire
Copyright Elsevier

Tektites are reduced (Fe2+) glasses formed by the quenching of molten material ejected from Earth’s surface as a result of a hypervelocity impact. The vast majority of tektites are usually homogeneous glasses, but rare samples containing mineral inclusions can provide insights about the source material, sample thermal history, and tektite formation process. Tektites from two distinct strewn fields presenting Ca-phosphate inclusions detected from anomalous magnetic susceptibility were studied: one sample from the Ivory Coast tektite (ICT) field ejected at 1.07 Ma from the Bosumtwi crater (10.5 km in size) in Ghana and two Muong Nong type samples from the Australasian tektite field (MN-AAT) ejected at 0.79 Ma from a crater possibly situated in southeast Asia. In ICT, Ca-phosphate inclusions are systematically embedded in lechatelierite (SiO2 glass). In MN-AAT Ca-phosphate are either embedded in lechatelierite or in Fe-rich glass forming schlieren. Multiscale petrographic characterization using correlative microscopy associating scanning electron microscopy, microprobe and, transmission electron microscopy reveals that rounded inclusions in ivoirite are composed of acicular Ca-phosphates (merrillite) embedded in an amorphous P-rich glass. In MN-AAT, inclusions consist mostly of single droplets of Fe-Mg rich Ca-phosphate (structurally related to apatite), but few droplets often forming an emulsion texture show a complex assemblage of apatite, magnetite, pyroxene, and spinel growing from a Pt-rich nucleus. Diffusion profile around lechatelierite domains reveals maximum temperatures greater than 2200–2400 °C in the impact plume of the Australasian tektite and the Ivory coast tektite. Heating time is of the order of seconds-tens of seconds rather than minutes as previously suggested (20 s for MN-AANT and 5 s for ICT). The number, the density, and the fact that inclusions are entirely crystallized in MN-AAT support relatively slow cooling rates (<200 °C/h), in comparison with the faster cooling rates (>2000 °C/h) indicated by the precipitation of amorphous P-rich glass in ICT. In both impact events, ejecta that had been heated to high temperatures did not remain in the vapor plume for an extended period of time and landed rapidly (within tens of seconds) at a relatively high temperature (>1000 °C) on the Earth’s surface.

Phosphate inclusions systematically embedded in lechatelierite in ICT provide clues about the source material. It suggests that the parent material for these silica-rich inclusions is not conventional detrital quartz. Rather, parts of lechatelierite domains may be inherited from a biogenic source that could be consistent with tropical soil (source of the phosphor) and its biomass (silica of plant origin). The reduction process that tektites record during their formation may be explained by superficial material since forests can contain a sizable mass of carbon that can reduce iron in tektites and produce platinoid-rich metallic nuclei and the Fe3+/ΣFe gradient recorded by the dendritic spinels.

Isaac J. Onyett^a, Martin Schiller^a, Mikael Stokholm^a, Jean Bollard^a, Martin Bizzarro^a,b
Earth and Planetary Science Letters 118986 Link to Article [https://doi.org/10.1016/j.epsl.2024.118985]
^aCentre for Star and Planet Formation, Globe Institute, University of Copenhagen, Copenhagen, Denmark
^bInstitut de Physique du Globe de Paris, Université de Paris Cité, Paris, France
Copyright Elevier

Chondrules, the principal high-temperature component of chondritic meteorites, may represent the fundamental building blocks of the terrestrial planets. The mass-independent isotope compositions of chondrules can be used to investigate their origins, as well as their subsequent transport and storage in the protoplanetary disk, which are weakly constrained. Debate surrounds whether mass-independent variability among chondrules arises from isotopically distinct precursor dust or small-scale addition of anomalous phases such as calcium-aluminium-rich inclusions (CAIs) and ameboid olivine aggregates (AOAs). Previous investigations employed isotope tracers that are concentrated in refractory inclusions (such as Ti), rendering them vulnerable to potential “nugget effects” arising from the presence of these anomalous phases and hindering their effectiveness as tracers of precursor dust compositions. An isotope tracer evenly distributed among silicates and thereby less sensitive to local additions from refractory inclusions, is essential to distinguish precursor dust compositions from minor additions of these phases. To address this challenge, we measured the mass-independent Si isotopic composition of chondrules from the carbonaceous Vigarano-type (CV) chondrites Allende and Leoville. Distinct isotopic signatures are observed in chondrules with different petrographic textures. Non-porphyritic chondrules exhibit ³⁰Si deficits akin to differentiated inner disk planetesimals, suggesting early formation within the inner disk (<1 Myr) before transportation to the CV accretion region in the outer disk. Conversely, porphyritic chondrules display a wide range of silicon isotope compositions, including both non-carbonaceous-like values and those exceeding bulk CV chondrites. Notably, non-porphyritic chondrules with substantial porphyritic igneous rims show compositional variations within individual chondrules, whereby cores retain ³⁰Si-depleted signatures while rims record more positive ³⁰Si compositions. Our findings show that contributions from isotopically anomalous refractory condensates cannot be the primary cause of mass-independent variability among chondrules in CV chondrites. Instead, we find that the observed compositional diversity in porphyritic chondrules results from the recycling of inner disk chondrules following the accretion of CI-like dust from the outer Solar System.

Dijun Guo^a et al. (>10)
Earth and Planetary Science Letters 118986 Link to Article [https://doi.org/10.1016/j.epsl.2024.118986]
^aState Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
Copyright Elevier

The Apollo basin, located in the northeastern part of the South Pole-Aitken (SPA) basin, represents one of the Moon’s most significant geological features, offering profound insights into the lunar interior structure, the effects of the SPA impact, and the history of lunar crust evolution. This study presents an in-depth geological analysis of the Apollo basin region, revealing the distribution of rock types and compiling a comprehensive geologic map that correlates with the lithologic and geochemical properties of the area. Utilizing the characteristics and compositional provenance of the geologic units, we have constructed schematic cross-sections that elucidate the interior structure and stratigraphic evolution of the Apollo basin region. Despite excavations of the SPA and Apollo impacts, the anorthositic crust of this area was not entirely removed and has been uplifted to shallow depths, making it more susceptible to exposure by subsequent impacts. Additionally, upper mantle material, characterized by ultramafic, low-Ca pyroxene, was excavated by the SPA impact and is present in the impact melt/breccias of the Apollo basin. After the formation of the Apollo basin, multiple mare units were emplaced over a period potentially spanning ∼1.5 billion years, with the oldest of these maria being superposed by substantial postdating basin ejecta. The results of this study strengthen our understanding of the geology and evolution of the Apollo and SPA basins and offer valuable insights for interpreting the exploration and sample analysis results of the Chang’e-6 mission.

James B. Garvin^a, Richard J. Soare^b 
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116303]
^aNASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
^bDept of Geography, Dawson College, Montreal H3Z 1A4, Canada
Copyright Elsevier

No abstract to this preface.

Zheng-Yu Long^a,b, Frédéric Moynier^a, Marine Paquet^a,c, James M.D. Day^d, Linru Fang^a, Tu-Han Luu^a, Dimitri Rigoussen^a, Kun-Feng Qiu^b, Jun Deng^b, Christian Koeberl^e
Earth and Planetary Science Letters 118979 Link to Article [https://doi.org/10.1016/j.epsl.2024.118979]
^aIstituto Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, 75005 Paris, France
^bFrontiers Science Center for Deep-time Digital Earth, State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences, Beijing, China
^cCentre de Recherches Pétrographiques et Géochimiques de Nancy, CNRS, Université de Lorraine 15 Rue Notre Dame des Pauvres 54500 Vandoeuvre-lès-Nancy, France
^dScripps Institution of Oceanography, University of California San Diego, La Jolla, CA, 92093-0244, USA
^eDepartment of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
Copyright Elevier

Evaporation can fractionate elements and their isotopes between the condensed and gas phases. The fractionation of zinc isotopes during impact-induced evaporation can be used to effectively determine the extent of volatile loss. A robust understanding of the Zn isotope system in assessing the volatile loss, however, relies on well-constrained empirical isotopic fractionation factors (α) during evaporation under a range of pressure and temperature conditions. In this study, Zn isotopic data for well-documented impact glasses from six sites (Darwin, Australia; Zhamanshin, Kazakhstan; El’gygytgyn, Russia; Boltysh, Ukraine; Lonar, India; and Ries, Germany) are reported to investigate the extent of Zn isotopic fractionation under conditions of impact-induced evaporation on Earth. Our findings suggest that the initial Zn isotopic composition in terrestrial impact glasses is comparable to that of continental crustal rocks, but this composition becomes progressively heavier as more isotopically light Zn is lost from the impact melt, reaching a maximum δ⁶⁶Zn value of +1.1 ‰. The investigated samples show a statistically significant negative correlation between δ⁶⁶Zn values and Zn contents, especially those from the Darwin crater (R² = 0.90). These samples define an α value of 0.99971 ± 0.00005 (1SE). This α value is consistent with those previously estimated for melt glasses and fused sands (α = 0.9997 to 0.9998) from the Trinity nuclear detonation site, slightly higher than the value estimated from tektites (α = ∼0.998), and notably higher than that theoretically expected for evaporation into a vacuum (α = 0.985 to 0.993). This result highlights the limited fractionation of Zn isotopes during terrestrial impact processes. Moreover, the modelling suggests that the range of α values from 0.9997 to 0.9998 aligns with the observed compositions in lunar mare basalts and products from nuclear detonation, supporting α values close to but not exactly unity for Zn isotopic fractionation during various high-energy impact events. Utilizing the modelled fractionation factor (α = 0.9997), it is possible to reproduce the Zn concentration and isotopic composition of the lunar mare basalts, indicating a loss of about 98 % of the Moon’s initial Zn inventory. Terrestrial impact glasses demonstrate that, under natural impact conditions, stable Zn isotopes can undergo evaporative fractionation to a degree comparable to lunar mare basalts and melted fallout glass and fused sands from nuclear detonation, suggesting an important contribution from impact to the volatile depletion of terrestrial planets.

G. Schmidt^a,b, F. Salvini^b  
Earth and Planetary Science Letters 118974 Link to Article [https://doi.org/10.1016/j.epsl.2024.118974]
^aIstituto di Astrofisica e Planetologia Spaziali (IAPS), INAF, Rome, Italy
^bGeoQuTe Lab, Department of Science, Roma Tre University, Rome, Italy
Copyright Elevier

Load on a planet’s lithosphere can often form a well-defined flexural bulge, including a permanent (or long-lasting) forebulge, which preserves important information on the force of the load and properties of the lithosphere itself. On Pluto, aspects of the outer ice shell (i.e. the lithosphere) have become increasingly ascertainable, as recent work using data from the New Horizons space probe has revealed evidence of ongoing surface cryovolcanism and a subsurface water ocean. However, the precise thickness and elasticity of the ice shell has yet to be fully established. Sputnik Planitia, one of the largest surface features on Pluto, is an elliptical depression that may have formed during an impact event and subsequently infilled with nitrogen ice. It is characterized by a smooth, radially asymmetrical, forebulge which has been retained in places along the border of the depression. However, the proportion of influence on the formation of the forebulge between the impact load and the load induced by the infill remains unknown. Here, we report results from the analysis of the forebulge of Sputnik Planitia to explore the characteristics of the ice shell and the nitrogen infill. By utilizing multiple Converging Monte Carlo (CMC) simulations within the material and environmental parameters of Pluto, the best fit flexure surface was able to replicate the topography of the flexure (including the forebulge) from ten profiles. Results show an ice shell thickness ranging from 65 to 90 km, with an average of 78 km. The density of the ice shell is 50 kg/m³ less than the density of the subsurface water ocean. We demonstrate that if the formation of the forebulge occurs solely from the nitrogen ice infill load, the infill must reach >18 km of thickness. Furthermore, a southeast-northwest central load symmetry may have been produced by an impacting object with a southeast-northwest trajectory.

Kees Erica R. JAWIN^1,2, Timothy J. MCCOY¹, Lisette E. MELENDEZ^1,3, Catherine M. CORRIGAN¹ , Kevin RIGHTER^4,8, and Harold C. CONNOLLY Jr^5,6,7 
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14263]
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
²Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC, USA
³Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA
⁴NASA Johnson Space Center, Houston, Texas, USA
⁵Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
⁶Department of Geology, School of Earth and Environment, Rowan University, Glassboro, New Jersey, USA
⁷Department of Earth and Planetary Science, American Museum of Natural History, New York, New York, USA
⁸Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York, USA Sciences

Orbital observations of Bennu revealed a surface covered in boulders that are most similar among meteorites in our collections to aqueously altered carbonaceous chondrites, and initial analyses of the returned Bennu sample have begun to reveal insights into Bennu’s origins. We identified a suite of paired CM2 chondrite meteorites that have a finely layered texture and bear a striking similarity, although at a different scale, to rugged, layered boulders on Bennu. We investigated the nature and potential origin of this layered texture by performing a petrofabric analysis on samples MET 00431, 00434, and 00435. We developed a micro-geospatial mapping framework that is more commonly used for landscape-scale investigations. Our results reveal a pervasive fracture network that exhibits a similar orientation to flattened particles dominated by tochilinite–cronstedtite intergrowths (TCI). We propose that their petrofabrics originated from a low-energy impact on the parent body that occurred after the main period of aqueous alteration halted. The impactdeformed TCI (which formed during earlier aqueous alteration) and generated the fractures. We propose that the sample from Bennu may contain particles with similar layered textures to these meteorites which, if present, would likewise indicate the dominant role of impacts and aqueous alteration on Bennu’s parent body.

T. Mark Harrison^a, Bidong Zhang^a,^b, Andrew F. Parisi^a, Elizabeth A. Bell^a 
Earth and Planetary Science Letters 118933 Link to Article [https://doi.org/10.1016/j.epsl.2024.118943]
^aState Department of Earth, Planetary and Space Sciences, University of California Los Angeles, Los Angeles, CA 90095, USA
^bDepartment of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, USA
Copyright Elevier

Investigations of Apollo-returned samples radically altered our understanding of lunar history which has important implications for terrestrial habitability and Solar System evolution. Radiometric dating of those samples inspired the hypothesis that Moon experienced a Late Heavy Bombardment (LHB) at ∼3.9 Ga. The LHB concept has come under several recent challenges, including the concern that ⁴⁰Ar/³⁹Ar step-heating dates of Apollo impactites had been misinterpreted. Ultraviolet laser ablation (UVLAMP) ⁴⁰Ar/³⁹Ar dates – with their capacity for much higher spatial resolution and thus potential to avoid dating near-ubiquitous clasts in impact melt rocks – should in principle provide more interpretable results. Here we compare new ion microprobe ²⁰⁷Pb/²⁰⁶Pb accessory mineral dates for two Apollo 17 impactites for which UVLAMP ⁴⁰Ar/³⁹Ar dates had been previously obtained. Our results are consistent with a single accessory phase growth event for each sample, though the two samples yielded statistically different mean ages of ca. 3.974±0.013 and 3.928±0.003 Ga. Both can reasonably be interpreted as dating an impact event, but the ²⁰⁷Pb/²⁰⁶Pb dates are older than the associated ⁴⁰Ar/³⁹Ar dates by several hundred million years. We interpret that the age differences result from subsequent thermal disturbances. The discordancy between impact ages inferred from lunar impactites using two different radiometric systems suggests caution in acceptance of the LHB hypothesis without the benefit of both larger lunar datasets and more multichronometric studies. Even with such information, our capacity to know the lunar bombardment history is likely limited by compositional and thermal effects which appear to restrict growth of impact-produced accessory minerals to a small fraction of the lunar surface. Using currently available datasets, the LHB hypothesis may be effectively untestable.

Uta Beyersdorf-Kuis^a,b, Ulrich Ott^a,b,c, Mario Trieloff^a
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.09.012]
^aMax-Planck Institute for Chemistry, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany
^bUniversity of Heidelberg, Im Neuenheimer Feld 234-236, D-69120 Heidelberg, Germany
^cInstitute for Nuclear Research Atomki, Bem tér 18/c, H-4026 Debrecen, Hungary
^dKlaus-Tschira-Labor für Kosmochemie, D-69120 Heidelberg, Germany de Lorraine, CNRS, CRPG, UMR 7358, Nancy, 
Copyright Elsevier

Excesses of cosmic-ray produced nuclei in individual components of meteorites indicate “pre-irradiation”, either in the surface region of their parent bodies or as free-floating small particles in the early Solar System. We expand on our earlier work (Beyersdorf-Kuis et al., 2015) and report a study of cosmic-ray produced He and Ne in chondrules and “matrix” (i.e., matrix-dominated) material of several CR2 and CV meteorites as well as the highly primitive, unique, carbonaceous chondrite Acfer 094. In accordance with previous work, no evidence for pre-irradiation was found for CV3 Allende, while for CV3 Vigarano evidence for pre-irradiation is marginal at best. Also, the single chondrule from unique Acfer 094 that we studied has a cosmic ray exposure indistinguishable from the one we found for “matrix” material. Chondrules from Acfer 082 (CV) exhibit both excesses and deficits relative to “matrix”, which points to pre-irradiation of not only chondrules, but also matrix material. A similar case may be Renazzo (CR2), where, however, the identification is complicated by the presence of abundant pre-solar Ne-E. A large number of chondrules (ten) were studied from CR2 El Djouf 001, which yielded slightly variable, small but consistent, excesses relative to “matrix”, corresponding to “nominal” (i.e., irradiation by galactic cosmic rays in 4π geometry) excess ages of 1 to 2 Ma. Modelling suggests contributions from irradiation in the parent body regolith by solar cosmic rays (SCR) as well as galactic cosmic rays (GCR), where the latter dominates. Reevaluating the large variations previously identified in chondrules from QUE 99177, we suggest either a very different regolith history compared to that of El Djouf 001 or, more likely, pre-irradiation by, primarily, GCR in the early solar system as suggested previously. The case of solar-wind-rich NWA 852 (CR2) shows similarity to El Djouf 001 except for a much larger size of the effects. We suggest that the situation may be common among meteorites with a regolith origin. With independent information on the cosmic ray exposure age, which could be obtained by the study of cosmic-ray produced radionuclides, the individual parent body contributions may be disentangled, providing constraints on regolith dynamics.