¹George D. Cody, ¹Conel M. O’D. Alexander, ¹Dionysis I. Foustoukos, ^1,2Yoko Kebukawa, ¹Ying Wang
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.09.023]
¹Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC, United States
²Tokyo Institute of Technology, Department of Earth and Planetary Science, Tokyo, Japan
Copyright Elsevier

Rotationally resonant Deuterium Nuclear Magnetic Resonance spectroscopy (D MAS NMR) was applied to IOM isolated from a CR1 chondrite Grosvenor Mountains (GRO) 95577 and a CM2 chondrite (Murchison). It is shown that in IOM D strongly prefers the aliphatic hydrogen reservoir over the aromatic hydrogen reservoir. For GRO 95577, that has a bulk δD of 3303 ‰ (Alexander et al., 2010), the average δD value of the aromatic reservoir is 1740 ± 128 ‰ and the aliphatic reservoir is 4477 ± 105 ‰, i.e., D/H enrichments of 1.27 and 0.64, respectively, relative to the bulk. For Murchison IOM, that has a bulk δD of 811 ‰ (Alexander et al., 2010), the average δD of the aromatic reservoir is 512 ± 88 ‰ and the aliphatic reservoir is 1033 ± 64 ‰ i.e., D/H enrichments of 1.12 and 0.82, respectively, relative to the bulk. D-H exchange between D-enriched water and a type III kerogen reveals nearly equivalent D up take by both aromatics and aliphatics. Laboratory synthesis of IOM-like material in the presence of D2O reveals a high degree of deuteration with a strong preferential deuteration of the aliphatic hydrogen reservoir indicating that the δD of the water during IOM synthesis is the primary determinant of syn-IOM’s δD. The IOM in GRO 95577 and Murchison (FA and H/C × 100) lie on the molecular evolution line as defined by the IOM of the Tagish Lake clasts and Murchison IOM has experienced more molecular evolution relative to that exhibited by GRO 95577 IOM. A forward prediction derived from the D/H ratios for the aliphatic and aromatic hydrogen reservoirs in Murchison and GRO 95577, relative to their bulk D/H ratios, derived from D MAS NMR, is applied to explain the origin of the Tagish Lake trend of δD vs molecular evolution (H/C × 100). The results of this forward prediction suggest that the Tagish Lake isotopic trend results from a combination of molecular evolution (loss of predominantly aliphatic H and D) and partial D-H exchange with D depleted chondritic water during a short-term hydrothermal alteration event. Such events may be faithfully identified in chondritic organic solids and be a common occurrence, but not necessarily revealed in the mineralogy of type 1 and 2 carbonaceous chondrites.

¹Samuel Ebert, ²Kazuhide Nagashima, ²Alexander N. Krot, ³Shigeru Wakita, ⁴Jean-Alix Barrat, ¹Addi Bischoff
Earth and Planetary Science Letters 646, 119010, Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.119010]
¹Institut für Planetologie, University of Münster, D-48149, Münster, Germany
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
³Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, Place Nicolas Copernic, F-29280, Plouzané Cedex, France
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) commonly observed in chondritic meteorites are the oldest dated solids formed in the Solar System. Short-lived isotope chronologies (²⁶Al-²⁶Mg, ¹⁸²Hf-¹⁸²W) suggest a ∼2 Ma gap between the formation of CAIs and the accretion of the final chondrite parent bodies. One thin section, 3.27 cm² in size, of an ordinary chondrite NWA 3358 (H3.1) studied contains 52 refractory inclusions (CAIs and amoeboid olivine aggregates (AOAs)) comprising 0.14 % of its area, which is the highest abundance of refractory inclusions among non-carbonaceous chondrites containing on average ∼0.009 area % of CAIs and AOAs. In combination with a low chondrule/matrix ratio of ∼1.5, this makes NWA 3358 a unique ordinary chondrite. The aqueously-formed fayalites (Fa_>99) in NWA 3358 have the inferred initial ⁵³Mn/⁵⁵Mn ratio of (5.56 ± 0.44) × 10⁻⁶ which is the highest measured value for secondary minerals in chondrites and corresponds to the formation time of ∼1.0–1.5 Ma after CAIs. Based on the ⁵³Mn-⁵³Cr chronology of fayalite formation and the thermal modeling, we infer that the first-generation of an H chondrite parent body, ∼6–12 km in diameter, accreted within 1.0 Ma after formation of CAIs, filling the gap of ∼2 Ma between CAIs and the earliest chondrite parent bodies. This early accretion provides a possible mechanism of CAIs/AOAs storage in the inner solar nebula and could explain the high amount of refractory inclusions in NWA 3358. A later destruction of these first-generation bodies may also explain the presence of CAIs and chondrules of different ages within later formed chondrite parent bodies.

^1,2Yishen Zhang, ^3,4,5Bernard Charlier, ⁴Stephanie B. Krein, ⁴Timothy L. Grove, ^1,5Olivier Namur, ⁵Francois Holtz
Earth and Planetary Science Letters 646, 118989 Link to Article [https://doi.org/10.1016/j.epsl.2024.118989]
¹Department of Earth and Environmental Sciences, KU Leuven, 3001 Leuven, Belgium
²Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
³Department of Geology, University of Liège, 4000 Sart Tilman, Belgium
⁴Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, Cambridge, MA 02139 USA
⁵Institut für Erdsystemwissenschaften, IESW, Abteilung Mineralogie, Leibniz Universität Hannover, 30167 Hannover, Germany
Copyright Elsevier

The latest stages of the lunar magma ocean (LMO) crystallization led to the formation of ilmenite-bearing cumulates and urKREEP, residual melts enriched in K, rare earth elements (REEs), P, and other incompatible elements. Those highly evolved lithologies had major impacts on the petrogenesis of lunar volcanic rocks and the compositional diversity of post-LMO magmatism resulting from mantle remelting. Here, we present new experimental results constraining the composition of the very last liquids produced during LMO crystallization. To test the potential role of silicate liquid immiscibility in the formation of urKREEP, synthetic samples representative of residual melts of bulk Moon compositions were placed in double platinum-graphite capsules at 1020–980 °C and 0.08–0.10 GPa in an internally-heated pressure vessel. The produced silicate liquids are multiply saturated with plagioclase, augite, silica phases, and ilmenite (± fayalitic olivine ± pigeonite). Our experiments show that the liquid line of descent reaches a two-liquid field at 1000 °C and >97% crystallization for a range of whole-Moon compositions. Under these conditions, a small proportion of silica-rich melt (70.0–71.4 wt.% SiO2, 6.4–7.3 wt.% FeO, 5.4–6.1 wt.% K2O, 0.2–0.3 wt.% P2O5) coexists within an abundant Fe-rich melt (42.6–44.1 wt.% SiO2, 27.6–28.8 wt.% FeO, 0.9–1.0 wt.% K2O, 2.8–3.2 wt.% P2O5) with sharp two-liquid interfaces. Our experimental results also constrain the relative onset of ilmenite crystallization compared to the development of immiscibility and indicate that an ilmenite-bearing layer formed in the lunar interior before immiscibility was attained. Using a self-consistent physicochemical LMO model, we constrain the thickness and depth of the ilmenite-bearing layer during LMO differentiation. The immiscible K-Si-rich and P-Fe-rich melts together also produced an immiscible urKREEP layer ∼2–6 km thick and ∼30–50 km deep depending on the trapped liquid fraction in the cumulate column (≤10%) and the thickness of the buoyant anorthosite crust (30–50 km). We provide constraints on the relationship between the compositions of immiscible urKREEP melts and those of KREEPy rocks. By modeling the mixing of KREEP-poor basalt and the immiscible melt pairs, we reproduce the K and P enrichments and apparent decoupling of K from P in KREEPy rocks. Our results highlight that processes such as the assimilation of evolved heterogeneous mantle lithologies may be involved in hybridization during post-LMO magmatism. The immiscible K-Si-rich lithology may also have contributed to lunar silicic magmatism.

¹Andrew G. Tomkins, ¹Erin L. Martin, ¹Peter A. Cawood
Earth and Planetary Science Letters 646, 118991 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.118991]
¹School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria 3800, Australia
Copyright Elsevier

All large planets in our Solar System have rings, and it has been suggested that Mars may have had a ring in the past. This raises the question of whether Earth also had a ring in the past. Here, we examine the paleolatitudes of 21 asteroid impact craters from an anomalous ∼40 m.y. period of enhanced meteor impact cratering known as the Ordovician impact spike, and find that all craters fall in an equatorial band at ≤30°, despite ∼70 % of exposed, potentially crater-preserving crust lying outside this band. The beginning of this period is marked by a large increase in L chondrite material accumulated in sedimentary rocks at 465.76 ± 0.30 Ma, which, together with the impact spike, has long been suggested to result from break-up of the L chondrite parent body in the asteroid belt. Our binomial probability calculation indicates that it is highly unlikely that the observed crater distribution was produced by bolides on orbits directly from the asteroid belt (P = 4 × 10–8). We therefore propose that instead, a large fragment of the L chondrite parent body broke up due to tidal forces during a near-miss encounter with the Earth at ∼466 Ma. Given the longevity of the impact spike and sediment-hosted L chondrite debris accumulation, we suggest that a debris ring formed after this break up event, from which material deorbited to produce the observed crater distribution. We further speculate that shading of Earth by this ring may have triggered cooling into the Hirnantian global icehouse period.

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.