¹Nicolas D. GARRONI,¹Gordon R. OSINSKI
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.13993]
¹Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

Carbonates from the impact melt-bearing breccia in the 2016 IODP/ICDPExpedition 364 drill core at Site M0077 were systematically documented and characterizedpetrographically and geochemically. Calcite, the only carbonate mineral present, is abundantthroughout this deposit as five distinct varieties: (1) subangular carbonate clasts (Type A); (2)subround/irregular carbonate clasts with clay altered rims (Type B); (3) fine-crystalline matrixcalcite (Type C); (4) void-filling sparry calcite (Type D); and (5) microcrystalline carbonatewith flow textures (Type E). Quantitative geochemical analysis shows that calcite in allcarbonate varieties are low in elemental impurities (<2.0 cumulative wt% on average);however, relative concentrations of MgO and MnO vary, which provides distinction betweeneach variety: MgO is highest in calcite from Types A, B, and C carbonates (0.2–0.8 wt% onaverage); MnO is highest in calcite from Types B, C, and D carbonates (0.2–1.3 wt% onaverage); and calcite from Type E carbonate is most pure (<0.1 wt% on average MgO andMnO, cumulatively). Based on textural and geochemical variations between carbonate types,we interpret that some of the carbonate target rocks melted during impact and wereimmiscible within the silicate-dominated melt sheet prior to the resurgence of seawater. TypeB clasts were formed by molten fuel–coolant interaction, as the incoming seawater erodedthrough the melt sheet and encountered carbonate melt (Type E). Post-impact meteoric-dominated hydrothermal activity produced the Mn-elevated calcite from Type C and Dcarbonates, and altered the Type B clasts to be elevated in Mn and host a clay-rich rim.

¹R.C. Greenwood et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13968]
¹Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
Published by arrangement with John Wiley & Sons

As part of an integrated consortium study, we have undertaken O, Cd, Cr, Si, Te, Ti, and Zn whole rock isotopic measurements of the Winchcombe CM2 meteorite. δ66Zn values determined for two Winchcombe aliquots are +0.29 ± 0.05‰ (2SD) and +0.45 ± 0.05‰ (2SD). The difference between these analyses likely reflects sample heterogeneity. Zn isotope compositions for Winchcombe show excellent agreement with published CM2 data. δ114Cd for a single Winchcombe aliquot is +0.29 ± 0.04‰ (2SD), which is close to a previous result for Murchison. δ130Te values for three aliquots gave indistinguishable results, with a mean value of +0.62 ± 0.01‰ (2SD) and are essentially identical to published values for CM2s. ε53Cr and ε54Cr for Winchcombe are 0.319 ± 0.029 (2SE) and 0.775 ± 0.067 (2SE), respectively. Based on its Cr isotopic composition, Winchcombe plots close to other CM2 chondrites. ε50Ti and ε46Ti values for Winchcombe are 3.21 ± 0.09 (2SE) and 0.46 ± 0.08 (2SE), respectively, and are in line with recently published data for CM2s. The δ30Si composition of Winchcombe is −0.50 ± 0.06‰ (2SD, n = 11) and is essentially indistinguishable from measurements obtained on other CM2 chondrites. In conformity with petrographic observations, oxygen isotope analyses of both bulk and micromilled fractions from Winchcombe clearly demonstrate that its parent body experienced extensive aqueous alteration. The style of alteration exhibited by Winchcombe is consistent with relatively closed system processes. Analysis of different fractions within Winchcombe broadly support the view that, while different lithologies within an individual CM2 meteorite can be highly variable, each meteorite is characterized by a predominant alteration type. Mixing of different lithologies within a regolith environment to form cataclastic matrix is supported by oxygen isotope analysis of micromilled fractions from Winchcombe. Previously unpublished bulk oxygen isotope data for 12 CM2 chondrites, when combined with published data, define a well-constrained regression line with a slope of 0.77. Winchcombe analyses define a more limited linear trend at the isotopically heavy, more aqueously altered, end of the slope 0.77 CM2 array. The CM2 slope 0.77 array intersects the oxygen isotope field of CO3 falls, indicating that the unaltered precursor material to the CMs was essentially identical in oxygen isotope composition to the CO3 falls. Our data are consistent with earlier suggestions that the main differences between the CO3s and CM2s reflect differing amounts of water ice that co-accreted into their respective parent bodies, being high in the case of CM2s and low in the case of CO3s. The small difference in Si isotope compositions between the CM and CO meteorites can be explained by different proportions of matrix versus refractory silicates. CMs and COs may also be indistinguishable with respect to Ti and Cr isotopes; however, further analysis is required to test this possibility. The close relationship between CO3 and CM2 chondrites revealed by our data supports the emerging view that the snow line within protoplanetary disks marks an important zone of planetesimal accretion.

¹A.В. VERCHOVSKY,¹F. A. J. ABERNETHY,¹M. ANAND,¹S. J. BARBER,¹R. FINDLAY,¹I. A. FRANCHI,¹R. C. GREENWOOD,¹M. M. GRADY
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.13983]
¹School of Physical Sciences, The Open University, Milton Keynes, UK
Published by arrangement with John Wiley & Sons

Two bulk Winchcombe along with six other CM2 meteorite samples weresubjected to quantitative evolved gas analysis. The observed release patterns for almost allvolatile species demonstrate close similarity for all the samples and especially between thosefor Winchcombe. This can be considered as a fingerprint for this petrological type ofmeteorites. We identified several gases including H2,H2O, O2, CO, CO2, and SO2releasedin different temperature ranges. The sources and mechanisms of their release were alsoestablished. Some of the gases, H2, CO, and CO2, are released as a result of oxidation ofmacromolecular organic material from oxygen derived from oxygen-bearing minerals (a partof CO2is also released as a result of decomposition of carbonates). The others, O2andH2O, are associated with the phase transformation/decomposition of phyllosilicates and(oxy)hydrates, while a high-temperature release of SO2is associated mostly with thedecomposition of sulfides and in few cases also with sulfates. A low-temperature release ofSO2is due to evaporation and oxidation of elemental sulfur from the meteoritic matrix andorganic material. The total concentrations of H (mostly represented by H2O), C, and S,calculated according to calibration of the quadrupole mass spectrometer with referencegases and decomposition of solid samples (CaSO42H2O and NaHCO3) are in reasonableagreement with those determined by independent methods. Variations in the ratio of thecarbon amounts released as CO2and CO (CCO2/CCO) between the samples could be anindicator of their terrestrial weathering.

¹Gordon R. OSINSKI,¹Adam B. COULTER,¹Roberta L. FLEMMING,¹Alexandra OZARUK,¹Annemarie E. PICKERSGILL,¹Alaura C. SINGLETON
Meteoritics & Planetary Science (in Press) Open Sccess Link to Article [doi: 10.1111/maps.13986]
¹Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

The~5 km diameter Gow Lake impact structure formed in the Canadian Shield ofnorthern Saskatchewan approximately 197 Myr ago. This structure has not been studied indetail since its discovery during a regional gravity survey in the early 1970s. We report hereon field observations from a 2011 expedition that, when combined with subsequentlaboratory studies, have revealed a wealth of new information about this poorly studiedCanadian impact structure. Initially considered to be a prototypical central peak (i.e., acomplex) impact structure, our observations demonstrate that Gow Lake is actually atransitional impact structure, making it one of only two identified on Earth. Despite its age,a well-preserved sequence of crater-fill impactites is preserved on Calder Island in themiddle of Gow Lake. From the base upward, this stratigraphy is parautochthonous targetrock, lithic impact breccia, clast-rich impact melt rock, red clast-poor impact melt rock, andgreen clast-poor impact melt rocks. Discontinuous lenses of impact melt-bearing brecciaalso occur near the top of the red impact melt rocks and in the uppermost green impactmelt rocks. The vitric particles in these breccias display irregular and contorted outlines.This, together with their setting within crater-fill melt rocks, is indicative of an origin asflows within the transient cavity and not an airborne mode of origin. Following impact, ahydrothermal system was initiated, which resulted in alteration of the crater-fill impactites.Major alteration phases are nontronite clay, K-feldspar, and quartz.

¹L.C. Chaves,¹M.S. Thompson,²M.J. Loeffler,³C.A. Dukes,⁴P.S. Szabo,¹B.H.N. Horgan 
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115634]
¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907, United States of America
²Department of Physics and Astronomy, Northern Arizona University, 527 South Beaver Street, Flagstaff, AZ 86011, United States of America
³Materials Science and Engineering, University of Virginia, 395 McCormick Road, Charlottesville, VA 22904, United States of America
⁴Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, United States of America
Copyright Elsevier

Magnetite is a relevant mineral component of asteroids as it has been identified in carbonaceous chondrites, on the surface of asteroid Bennu through remote sensing observations, and in samples returned from asteroid Ryugu. However, the effects of space weathering processes on magnetite have not yet been explored. To investigate how this mineral phase responds to space weathering, here we simulate micrometeoroid bombardment and solar wind irradiation of magnetite using pulsed laser and ion irradiation experiments. We performed X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and visible to near-infrared (VNIR) reflectance spectroscopy analyses to characterize the chemical, microstructural, and spectral response of magnetite to simulated space weathering. In addition, we carried out ion impact simulations using the SDTrimSP software to evaluate the calculated response of magnetite to 1 keV H⁺ and 4 keV He⁺ ions and compared these results to our XPS and TEM results. Ion irradiation simulated ~750 years on the surface of asteroid Bennu, with a solar-wind appropriate total H:He fluence ratio (~24). Within this time, depletion of O was observed with H⁺ and He⁺ ion irradiation, with significantly greater change via protons due to the larger fluence, where preferential sputtering promotes the formation of a metallic iron layer at the magnetite surface. This suggests that solar wind ions act as reducing agents on Fe oxides, with a fraction remaining implanted in these phases. Indeed, we observe elongated defects contained in a crystalline rim created by He⁺ implanted ions in the TEM. Pulsed laser irradiation, analogous to micrometeoroid impacts, generates melts on the surface of the magnetite grains. The impact melts and H⁺-generated metallic iron rims both result in increased VNIR spectral reflectance, but lower fluence He⁺ implantation has no significant spectral effect. These results suggest that space weathered magnetite could contribute to bright regions detected in remote sensing analyses of the Ryugu and Bennu surfaces by the Hayabusa2 and OSIRIS-REx missions and will contribute to the identification and interpretation of space weathered magnetite in returned samples retrieved from both asteroids.

¹Ziyan Han,^1,2,3Hejiu Hui,^1,2Haizhen Wei,^1,2Weiqiang Li
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.05.007]
¹State Key Laboratory of Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
¹CAS Center for Excellence in Comparative Planetology, Hefei 230026, China
³CAS Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Copyright Elsevier

The Moon is depleted in volatile elements and compounds, and lunar samples exhibit a wide range of Cl isotopic compositions, which is believed to result from the volatilization of metal chlorides (e.g., NaCl, KCl, and FeCl2). However, the Cl isotopic fractionation behavior during volatilization is not well constrained, particularly for metal chlorides. Furthermore, the effect of metal chloride evaporation on metal isotopes is poorly known. In the present study, we performed NaCl and KCl sublimation experiments to study Cl and K isotopic fractionations at temperatures ranging from 923 K to 1061 K and at pressures of 7×10–5 bar to 1 bar in an N2 atmosphere. The isotope fractionation factors of 37/35Cl(αgas–solid) from NaCl sublimation experiments are 0.9985±0.0002, 0.9958±0.0004, and 0.99807±0.00004 at 1, 10–2, and 7×10–5 bar, respectively. Those of 41/39K(αgas–solid) and 37/35Cl(αgas–solid) from KCl sublimation experiments are 0.99884±0.00004 and 0.9988±0.0003 at 1 bar, 0.9977±0.0002 and 0.9972±0.0003 at 10–2 bar, and 0.9989±0.0002 and 0.9989±0.0001 at 7×10–5 bar, respectively. Chlorine and K isotopes fractionate more at 10–2 bar than at 7×10–5 bar and 1 bar. The saturation index in all the sublimation experiments was >95%, which resulted in near-equilibrium isotopic fractionation at the sublimation interface. Therefore, the isotopic fractionation was controlled by mass transfer processes in the gas and solid phases. The isotopic fractionation at 10–2 bar was controlled by the chemical diffusion of sublimated gas in an N2 atmosphere with almost no convection effect, (i.e., Pe number close to zero), whereas the isotopic fractionation at 1 bar was suppressed by atmospheric convection with a turbulence factor of 0.4±0.1 (i.e., Pe number >1). The extremely high sublimation rate and the very slow diffusion in the sublimating solid at 7×10–5 bar suppressed isotopic fractionations. Based on our experimental results, calculations using Cl/K and Na/K in lunar materials reveal that degassing of KCl contributed very little (<0.2‰) to the K isotopic fractionation (>0.58‰) during lunar magma ocean degassing. The Cl isotopic fractionation factor from lunar samples is similar to our results at 10–2 bar. This similarity of Cl isotope fractionation indicates that there may have been a transient atmosphere above the lunar magma ocean.

¹Noriyuki KAWASAKI,²Daiki YAMAMOTO,³Sohei WADA,¹Changkun PARK,³Hwayoung KIM,⁴Naoya SAKAMOTO,^1,4Hisayoshi YURIMOTO
Meteoritics & Planetary Science (in Press) Link to Article [doi: 10.1111/maps.13989]
¹Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
²Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
³Division of Earth-System Sciences, Korea Polar Research Institute, Incheon, Republic of Korea
⁴Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo, Japan
Published by arrangement with John Wiley & Sons

Al–Mg mineral isochron studies using secondary ion mass spectrometry (SIMS)have revealed the initial26Al/27Al ratios, (26Al/27Al)0, for individual Ca-Al-rich inclusions(CAIs) in meteorites. We find that the relative sensitivity factors of27Al/24Mg ratio forSIMS analysis of hibonite, one of the major constituent minerals of CAIs, exhibit variationsbased on their chemical compositions. This underscores the critical need for usingappropriate hibonite standards to obtain accurate Al-Mg data. We measured the AlMgmineral isochron for hibonite in a fine-grained CAI (FGI) from the Northwest Africa 8613reduced CV chondrite by SIMS using synthesized hibonite standards with27Al/24Mg of~30,~100, and~400. The obtained mineral isochron of hibonite in the FGI yields (26Al/27Al)0of(4.730.09)9105, which is identical to that previously obtained from the mineralisochron of spinel and melilite in the same FGI (Kawasaki et al., 2020). The uncertainties of(26Al/27Al)0indicate that the constituent minerals in the FGI formed within~0.02 Myr inthe earliest solar system. The disequilibrium O-isotope distributions of the minerals in theFGI suggest that the O-isotope compositions of the nebular gas from which they condensedunderwent a transitional change from16O-rich to16O-poor within~0.02 Myr in the earliestsolar system. Once formed, the FGI may have been removed from the forming regionwithin~0.02 Myr and transported to the accretion region of the parent body.

¹M. Fastelli,²B. Schmitt,²P. Beck,²O. Poch,¹A. Zucchini,¹F. Frondini,¹P. Comodi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115633]
¹Department of Physics and Geology, University of Perugia, I-06123 Perugia, Italy
²Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
Copyright Elsevier

We analyse the quantitative effects of viewing geometry variations on the near-infrared reflectance spectra of mascagnite-(NH4)2SO4 and salammoniac-NH4Cl samples. Bi-directional reflectance spectra are collected in the 1–4.2 μm range considering a set of 3 incidence (i) angles (i = 0°; 30°; 60°) and 9 emergence (e) angles between −70° and 70° at room temperature and computed with respect to the normal direction. The NH4+ overtone and combinations bands located at ~1.09, 1.32, 1.62, 2.04, 2.2 and 3.05 μm are experimentally investigated. The bidirectional reflectance spectra of these samples show significant variations with the observation geometry in terms of reflectance values, spectral slope, and absorption bands parameters. The band positions remain essentially unchanged by varying the incident and emergence angles. On the other hand, bands’ area and depth show the highest variability for i ≥ 30° and e greater than ±40°(up to a factor 2.3 in relative mean variation). The area and depth parameters of these bands show a dual behaviour: (i) for the weak-medium spectral features below 2 μm the area and depth decrease as the phase angle increases. (ii) The strong spectral features above 2 μm increase their values only at phase angles above 90°, but also at low phase angles for high incidences, i ≥ 30°. This behaviour is linked both to the non-linear radiative transfer in particulate media and to the way the band depth and area are defined, relative to the local continuum. We observe important dependence (up to ~60% relative mean variation) of band depth and area on the incidence angle, up to 60°, compared to moderate variation with emergence angles (up to ~20% relative mean variation). Furthermore, the ~3 μm features becomes more saturated at ±70° emergence angles. A general trend of spectral bluing with change in observation geometry is observed. The current dataset is a contribution in the framework of present and future space missions focused on understanding the nature and quantification of ammonium-bearing minerals on icy bodies. The NH4+ − bearing minerals identification could provide information on: (i) ocean/brine compositions, (ii) possible explanations of geological phenomena and (iii) implications for biological activity.

¹C.P. Haupt,¹C.J. Renggli,¹M. Klaver,¹E.S. Steenstra,¹J. Berndt,¹A. Rohrbach,¹S. Klemme
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115625]
¹Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Münster 48149, Germany
Copyright Elsevier

The origin of young Chang’e 5 (CE5) lunar basalts is highly debated. We present results from high-pressure, high-temperature (P-T) phase equilibria experiments, and from petrological modeling, to constrain the depth and temperature of the source of these unique mare basalts. The experimental results indicate that the CE5 basalts could have formed either by melting clinopyroxene and Fesingle bondTi oxide-rich cumulates in the shallow lunar mantle, or by extreme fractional crystallization of a hot Mg-rich parental melt. Our findings corroborate the local preservation of significant heat (of at least 1200 °C) in the lunar mantle that is needed to generate basaltic melts of CE5 compositions at 2 Ga. We argue that the CE5 basalts are most likely formed by melting of Fe and Ti-rich cumulates in the shallow lunar mantle as extreme fractional crystallization of olivine and plagioclase from picritic parental melts requires too high temperatures in the lunar mantle (> 1500 °C) at ~2 Ga.

¹Marceau Lecasble,¹Sylvain Bernard,¹Jean-Christophe Viennet,¹Isis Criouet,¹Laurent Remusat
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115603]
¹Muséum National d’Histoire Naturelle, Sorbonne Université, CNRS UMR 7590, IMPMC, Paris, France
Copyright Elsevier

A variety of polycyclic aromatic hydrocarbons (PAHs) are reported in carbonaceous chondrites (CCs) and in the interstellar medium (ISM). Although PAHs in CCs are not as large as those detected in the ISM, their carbon isotope composition is interpreted as pinpointing an interstellar origin. In contrast, their hydrogen isotope composition can be related to the extent of secondary processes, as is the proportion of alkylated PAHs within CCs. Here, we experimentally investigate the molecular and isotopic evolution of PAHs under simulated asteroidal hydrothermal conditions at 150 °C. Results show that PAHs are chemically stable under these conditions whatever their size, i.e. no destruction, conjugation nor alkylation occurs, even in the presence of other reactive organic molecules. Plus, PAHs retain their carbon isotope compositions even in the presence of another carbon-rich reservoir, either organic or inorganic. On the other hand, their hydrogen isotope composition is modified through exchange with water. Of note, as shown by additional experiments, the presence of smectites, abundant in CCs, impacts the relative abundances of extractable PAHs, saponite trapping more efficiently the larger PAHs. Altogether, results of the present experiments show that PAHs of CCs can be used as tracers of both pre-accretion and secondary processes.