¹Wen Yu,¹Xiaojia Zeng,¹Xiongyao Li,¹Hong Tang,¹Jianzhong Liu
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2024JE008487]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
Published by arrangement with John Wiley & Sons

Precisely constraining the shock pressure of a Mars sample is critical for revealing the shock condition, geological process, and habitability of the Martian surface. The crystal structure of plagioclase is sensitive to the moderate shock pressure, such that its infrared spectra may record the shock state of Martian materials. In this study, we present a new way for quantifying the shock pressure via the micro-FTIR spectra of plagioclase by re-analyzing the published spectra of experimental shocked feldspars. Using the absorption area of micro-FTIR in the range of ∼1,000–1,150 cm−1, the shock pressures of plagioclases from three types of Mars meteorites were constrained. The results show that the nakhlite Northwest Africa (NWA) 10645, shergottite Tindouf 002, and martian breccia NWA 11220 have the shock pressure of 18.5 ± 5.2 GPa, >30 GPa, and 0–24.2 GPa, respectively. Our work demonstrates that the micro-FTIR spectra of plagioclase is not only a quantitative tool for constraining the moderate shock pressure (<30 GPa) of Martian materials but also a useful technique for recognizing the high-pressure phase maskelynite from plagioclase-glass and evaluating the shock effects of Mars samples. In the future, this method will be available for the analysis of Mars samples returned by China’s Tianwen-3 mission in around 2030.

^1,2Amanda Ostwald,¹Arya Udry,^3,4Juliane Gross,⁵James M.D. Day,⁶Sammy Griffin
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.06.033]
¹Department of Geoscience, University of Nevada, Las Vegas, Lilly Fong Geoscience Building, 4505 S Maryland Pkwy, Las Vegas, NV 89154, USA
²Smithsonian National Museum of Natural History, 10th St. & Constitution Ave. NW, Washington, DC 20560, USA
³NASA Johnson Space Center, 2101 E NASA Pkwy, Houston, TX 77058, USA
⁴Department of Earth and Planetary Science, Rutgers University, Busch Campus, 610 Taylor Rd, Piscataway, NJ 08854, USA
⁵Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0244, USA
⁶University of Glasgow, Glasgow G12 8QQ, United Kingdom
Copyright Elsevier

Nakhlites (clinopyroxene-rich cumulates) and chassignites (dunites) are two types of meteorites that were emplaced onto — and subsequently ejected from— the surface of Mars together, but their petrogenetic history has been difficult to discern. We studied the primary magmatic history preserved in zoning patterns of cumulus phases from a suite of nakhlites and chassignites. Samples studied include nakhlites Northwest Africa (NWA) 11013, NWA 10645, Governador Valadares, Caleta el Cobre 022, Nakhla, Miller Range 090032, and NWA 817, as well as chassignites NWA 2737 and Chassigny. In nakhlite and chassignite olivine, phosphorous (P) preserves primary magmatic signatures, and P2O5 ranges from ∼<0.01 to 0.21 wt %; in nakhlite pyroxene, chromium (Cr) zoning corresponds to Cr2O3 abundances between ∼0.03 to 0.36 wt %. We find that nakhlite pyroxene cores uniformly formed rapidly for a time at high crustal pressures, and then slowly at near-equilibrium under lower crustal pressures. Pyroxene in the nakhlites were then stored through multiple injections of magma prior to remobilization, eruption, and final crystallization. Nakhlite olivine cores are morphologically heterogenous throughout the suite, but all record rapid initial crystallization prior to equilibrium formation, followed by resorption in changing magma compositions. Both olivine and pyroxene in the nakhlites are antecrysts, as they initially formed in a different magma than that in which they erupted. Chassignites underwent very rapid initial undercooling, and record later changes in magma conditions, resulting in thin elemental oscillatory zoning patterns in olivine grains. Together, the cumulus phases of the nakhlite and chassignite suite, combined with petrological evidence from martian shergottite meteorites, suggest that significant magmatic undercooling is the rule rather than the exception for martian magmatic systems. This may relate to the stalling of magmas within the thicker crust of Mars, fostering crystal storage with significant temperature differences between injected magmas and crystal mushes.

¹Dante S. Lauretta et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14227]
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
Published by arrangement with John Wiley & Sons

On September 24, 2023, NASA’s OSIRIS-REx mission dropped a capsule to Earth containing ~120 g of pristine carbonaceous regolith from Bennu. We describe the delivery and initial allocation of this asteroid sample and introduce its bulk physical, chemical, and mineralogical properties from early analyses. The regolith is very dark overall, with higher-reflectance inclusions and particles interspersed. Particle sizes range from submicron dust to a stone ~3.5 cm long. Millimeter-scale and larger stones typically have hummocky or angular morphologies. Some stones appear mottled by brighter material that occurs as veins and crusts. Hummocky stones have the lowest densities and mottled stones have the highest. Remote sensing of Bennu’s surface detected hydrated phyllosilicates, magnetite, organic compounds, carbonates, and scarce anhydrous silicates, all of which the sample confirms. We also find sulfides, presolar grains, and, less expectedly, Mg,Na-rich phosphates, as well as other trace phases. The sample’s composition and mineralogy indicate substantial aqueous alteration and resemble those of Ryugu and the most chemically primitive, low-petrologic-type carbonaceous chondrites. Nevertheless, we find distinct hydrogen, nitrogen, and oxygen isotopic compositions, and some of the material we analyzed is enriched in fluid-mobile elements. Our findings underscore the value of sample return—especially for low-density material that may not readily survive atmospheric entry—and lay the groundwork for more comprehensive analyses.

^1,2Donald A. Hendrix,¹Tristan Catalano,¹Hanna Nekvasil,¹Timothy D. Glotch,^1,3Carey Legett IV,¹Joel A. Hurowitz
Meteoritics & Planetary Science (in Press)  Link to Article [https://doi.org/10.1111/maps.14228]
¹Department of Geosciences, Stony Brook University, Stony Brook, New York, USA
²National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA
³Intelligence and Space Research, Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Published by arrangement with John Wiley & Sons

Crewed missions to the Moon may resume as early as 2026 with NASA’s Artemis III mission, and lunar dust exposure/inhalation is a potentially serious health hazard that requires detailed study. Current dust exposure limits are based on Apollo-era samples that spent decades in long-term storage on Earth; their diminished reactivity may lead to underestimation of potential harm that could be caused by lunar dust exposure. In particular, lunar dust contains nanophase metallic iron grains, produced by “space weathering”; the reactivity of this unique component of lunar dust is not well understood. Herein, we employ a chemical reduction technique that exposes lunar simulants to heat and hydrogen gas to produce metallic iron particles on grain surfaces. We assess the capacity of these reduced lunar simulants to generate hydroxyl radical (OH*) when immersed in deionized (DI) water, simulated lung fluid (SLF), and artificial lysosomal fluid (ALF). Lunar simulant reduction produces surface-adhered metallic iron “blebs” that resemble nanophase metallic iron particles found in lunar dust grains. Reduced samples generate ~5–100× greater concentrations of the oxidative OH* in DI water versus non-reduced simulants, which we attribute to metallic iron. SLF and ALF appear to reduce measured OH*. The increase in observed OH* generation for reduced simulants implies high oxidative damage upon exposure to lunar dust. Low levels of OH* measured in SLF and ALF imply potential damage to proteins or quenching of OH* generation, respectively. Reduction of lunar dust simulants provides a quick cost-effective approach to study dusty materials analogous to authentic lunar dust.

¹Shunpei Yokoo,^1,2Kei Hirose
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.06.027]
¹Department of Earth and Planetary Science, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
²Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan
Copyright Elsevier

Recent seismological studies of the Martian core revealed its relatively low density, suggesting the presence of large amounts of light elements including oxygen and carbon in addition to sulfur. In order to reveal crystallizing solids in the light-element-rich core of Mars, we performed high-pressure melting experiments on Fe-S-O-C alloys at 26–49 GPa using a laser-heated diamond-anvil cell. The liquidus phase relations in the Fe-S-O-C system were determined based on textural and chemical characterizations of recovered samples. The results show that Fe-S-O-C liquids crystallize FeO or Fe₃C in the presence of small amounts of O or C in liquids. Accordingly the liquidus fields of Fe₃S and Fe₂S are small, and the quaternary eutectic point is found to be close to the Fe-Fe₃S binary eutectic point. Under Martian core conditions, S-rich liquids have low liquidus temperatures to crystallize FeO or Fe₃C compared to S-poor liquids. The pressure dependence of liquidus temperatures suggests that crystallization of Mars’ core starts at the center upon cooling. According to the FeO-Fe₃C cotectic surfaces and their liquidus temperatures, an FeO and/or Fe₃C inner core is predicted unless the Martian core remains entirely liquid.

¹Hiroharu Yui et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.06.016]
¹Department of Chemistry, Tokyo University of Science, Tokyo 162-8601, Japan
Copyright Elsevier

The surface chemistry of pyrrhotites from intact particles directly collected from asteroid (162173) Ryugu was investigated by micro-Raman spectroscopy. The Raman peak characteristic to pyrrhotite was observed at around 115 cm−1 in Ryugu pyrrhotites, similar to freshly cleaved surfaces of terrestrial pyrrhotites. Additional Raman bands centered at around 220, 275, and 313 cm−1 with broadened features were also detected from the Ryugu pyrrhotites. The set of Raman bands at 220 and 275 cm−1 was assigned to typical Fe-S stretching vibrations of ν2 (225 cm−1) and ν1 (275 cm−1). These bands are not clearly observed in bulk crystals of pyrrhotite but appear in its nanoparticulate phase. These bands are ordinarily seen in amorphous monosulfides that formed under low oxygen fugacity (fO2) conditions in nature, indicating that the structural alteration of pyrrhotite surfaces occurred heterogeneously on the nanoscale under low fO2 conditions. Further, the Raman band at 313 cm−1 was attributed to a characteristic tetrahedral bonding of Fe(III) in the lattice of FeII1-3xFeIII1-2xS, followed by the local breakdown of the crystal lattice structures from planar bonding with Fe(II). In addition, some areas of the Ryugu pyrrhotite grains showed corroded structures with iridescence. Furthermore, assemblages of magnetite particles were also preferentially observed on small areas of the likely-dissolved pyrrhotite crystals in phyllosilicate matrices. These characteristic features in the Raman spectra and in corroded structures of Ryugu pyrrhotites record changes in the local environmental conditions via aqueous alteration. The corrosion of pyrrhotite crystals followed by the preferential formation of magnetite particles by asteroidal water it the likely product of dissolution of Fe(II) from the pyrrhotite surface and its oxidative precipitation in microchemical environments on the Ryugu parent body.

¹Mingming Zhan,¹Kohei Fukuda,²Michael J. Tappa,³Guillaume Siron,²William O. Nachlas,⁴Makoto Kimura,¹Kouki Kitajima,²Ann M. Bauer,¹Noriko T. Kita
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.06.018]
¹WiscSIMS, Department of Geoscience, University of Wisconsin–Madison, Madison, WI 53706, USA
²Department of Geoscience, University of Wisconsin–Madison, Madison, WI 53706, USA
³Laboratoire Chrono-Environnement, Université de Franche-Comté, UMR 6249, 25000 Besançon, France
⁴National Institute of Polar Research, Meteorite Research Center, Midoricho 10-3, Tachikawa, Tokyo 190-8518, Japan
Copyright Elsevier

The mechanism of gas-melt interactions and the compositions of precursors are key to understanding the formation of chondrules. To shed light on the two enigmas, we studied the petrography, chemistry, and oxygen isotopes of six Al-rich chondrules (ARCs, five glassy and one plagioclase-bearing) in unequilibrated ordinary chondrites (OCs, petrologic subtype: 3.05). The plagioclase-bearing ARC was also investigated with Al-Mg chronology. Elemental zonation and inter-element correlations in glassy mesostasis of two ARCs indicate the condensation of gaseous Mg, SiO, Fe, and Na onto chondrule melt. The plagioclase-bearing ARC appears to display internal mass-independent oxygen isotope fractionation with δ18O increasing following the order of mineral crystallization, suggesting partial oxygen isotope exchange with ambient gas during crystallization. Oxygen isotopes of the six ARCs are distributed along a mixing line of slope = 0.99 ± 0.05, which intersects with calcium-aluminum-rich inclusions (CAIs), consistent with a small portion of OC type IA chondrules, but deviates from other OC ferromagnesium chondrules (FMCs) towards higher δ17O, suggesting that OC ARCs and some IA chondrules were established by interactions between CAI-like melts and 16O-poor ambient gas, rather than simply remelting solid mixtures of CAI and FMC materials.

All ARCs have unfractionated refractory lithophile element patterns with bulk concentrations ranging from ∼7 × CI to ∼15 × CI, indicating ∼ 30–100 % of CAI-like materials in their precursors. Their bulk compositions are linearly evolved toward the Mg: SiO ∼ 3:2 to 2:1 (in atomic) apex, consistent with adding gaseous Mg and SiO to the chondrule bulk via gas–melt interactions. The back-calculated compositions of the recycled CAI-like materials closely overlap with pyroxene-anorthite-rich CAIs, suggesting that extensive interactions between the melt of pyroxene-anorthite-rich CAI-like materials and ambient gas could make OC ARCs. The Al-Mg age of the plagioclase-bearing ARC is ∼2.2 Ma after CAIs, similar to typical OC FMCs, suggesting that the refractory component arrived in the OC reservoirs at the end of the chondrule heating events.

^1,2Qingshang Shi et al. (>10)
Geochmica et Cosmochimica acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.06.011]
¹State Key Laboratory of Geological Processes and Mineral Resources, Frontiers Science Center for Deep-time Digital Earth, China University of Geosciences, Beijing 100083, China
²School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, China
Copyright Elsevier

To investigate the chemical variation during space weathering of young mare basalts, here we report elemental, radiogenic Sr-Nd and stable Fe-Mg-Ca isotopic data of Chang’E-5 sieved soils and breccias. From the coarse fraction to the fine one, the sieved soils display increasing Al2O3 (10.34 wt%–13.36 wt%) and Sr (248 ppm–307 ppm) but decreasing FeO (23.50 wt%–20.22 wt%), MgO (6.88 wt%–5.78 wt%), FeO/Al2O3 (2.27–1.51) and MgO/Al2O3 (0.67–0.43). The contents of rare earth elements (except Eu) and high field strength trace elements do not vary with particle size but correlate with P2O5 contents. Given the limited contribution from contamination by meteorites and exotic materials ejected far away from the landing site, these elemental variations can be explained by differential comminution and distribution behaviors of plagioclase and mesostasis phases. These sieved soils yield a Sm-Nd isochron age (1.84 ± 0.83 Ga) comparable to that of basaltic clasts obtained by U-Pb dating (∼2.0 Ga). However, their Rb-Sr isotopic system is disturbed as indicated by their relatively homogeneous 87Sr/86Sr (0.701425–0.701592) despite variable Rb/Sr (0.017–0.028). These results suggest the Sm-Nd isotopic system is more robust to impact disturbance during space weathering compared to the Rb-Sr isotopic system. Given that the bulk soil still plots on the 2.03 Ga Rb-Sr reference isochron from the pristine plagioclases in CE-5 basalts, this disturbance did not affect the Rb-Sr isotopic system on the bulk scale. The CE-5 bulk soil has higher Mg# (33.6), 87Rb/86Sr (0.06) and present-day 87Sr/86Sr (0.701542) than the mean composition of reported basaltic clasts (Mg#: ∼28; 87Rb/86Sr: ∼0.038; 87Sr/86Sr: ∼0.700941), possibly implying that the bedrocks in CE-5 landing site consist of multiple magma pulses. The δ56Fe (0.122 ± 0.002 ‰ to 0.199 ± 0.008 ‰) and δ26Mg (−0.204 ± 0.016 ‰ to −0.109 ± 0.006 ‰) of sieved CE-5 soils increase with decreasing particle sizes but their δ44/42Ca (0.38 ± 0.04 ‰ to 0.44 ± 0.02 ‰) are relatively homogeneous. Mass balance modelling indicates that differential comminution has limited influence on the Fe-Mg-Ca stable isotopic compositions. We further dismiss the role of solar-wind sputtering, as Ca and Mg are more susceptible to sputtering and thus would be expected to show larger isotope fractionations compared to Fe, which is inconsistent with the observations. Free evaporation may explain the elevated δ56Fe and δ26Mg in fine fractions at given very limited depletion in FeO and MgO. The observed positive correlation between δ56Fe and δ26Mg, however, is much steeper than the slope expected for free evaporation, indicating also other mechanisms (e.g., Fe-Mg inter-diffusion). Since the CE-5 soil has a unique composition compared with Apollo and Luna soils, the chemical differentiation identified in this study provides new insights for establishing a connection between the chemistry and reflectance spectral properties of lunar soil. Our combined Fe-Mg-Ca isotopic study also provides a paradigm to distinguish the role of solar-wind sputtering and impact evaporation, and shows that the inter-particle diffusion process may be an important mechanism for the isotope fractionation among lunar soil components.

^1,2Yankun Di,²Qing-Zhu Yin,³François L.H. Tissot,^1,4Yuri Amelin
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Artile [https://doi.org/10.1016/j.gca.2024.06.012]
¹Research School of Earth Sciences, Australian National University, Acton, ACT 2601, Australia
²Department of Earth and Planetary Sciences, University of California Davis, Davis, CA 95616, USA
³The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
⁴Korea Basic Science Institute, Building 202, 162 YeonGu DanJi-ro, Ochang, Cheongwon, Cheongju, Chungbuk 28119, Republic of Korea
Copyright Elsevier

We introduce a new isotope chronological model in which the natural mass-dependent isotopic fractionation effects of the radioactive (“parent”) and radiogenic (“daughter”) elements are systematically and rigorously considered. Using this model, we show that internally-normalized radiogenic isotopic ratios, commonly determined for daughter elements such as Sr, Nd, Cr, Ni, Hf, W, and Os, are dependent on the extent of natural isotopic fractionation of the daughter and parent elements at the time of system closure. This dependence indicates that (1) in two samples derived from the same isotopically homogeneous source at the same time and with identical radiogenic ingrowth over time, the present-day internally-normalized radiogenic isotope ratios would be different if they were initially fractionated to different degrees, and (2) if different internally-normalized radiogenic isotopic ratios are observed for two co-genetic objects, the difference between them would include contributions from both radiogenic ingrowth and natural isotopic fractionation. Consequently, the isochron dating equations employed in traditional chronological studies will yield inaccurate results when significant natural isotopic fractionation are present among the studied samples. Modified isochron equations that can be used to retrieve correct chronological information from isotopically-fractionated samples are presented. These theoretical considerations are applied to the 87Rb–87Sr, 147Sm–143Nd, and 146Sm–142Nd isotope systems of calcium–aluminium-rich inclusions (CAIs), a set of samples that have undergone significant natural Sr, Nd, and Sm isotope fractionation during their formation. The large natural Sr isotope fractionation (up to ca. 5.3 ‰ for 88Sr/86Sr) in fine-grained CAIs can generate analytically well-resolvable biases (>120 ppm) in the internally-normalized 87Sr/86Sr ratios and lead to significant scatters of their 87Rb–87Sr isochron (in conjunction with scatters induced by open-system disturbances). The 87Rb–87Sr systems of coarse-grained CAIs, on the contrary, are essentially not affected by natural Sr isotopic fractionation due to their much subdued fractionation degrees, resulting in a more robust isochron. Similarly, the large natural Nd (up to ca. 4.0 ‰ for 146Nd/144Nd) and Sm (up to ca. 7.1 ‰ for 152Sm/148Sm) isotopic fractionation in fine-grained CAIs can induce significant scatters of the 147Sm–143Nd isochron if the natural fractionation followed the kinetic or power law, and 146Sm–142Nd isochron if the natural fractionation followed the equilibrium, Rayleigh, or power law. This implies that when studying radioactive isotope systems in objects whose daughter and parent elements can undergo significant isotope fractionation in nature, accompanying stable isotope analyses are necessary for accurate chronological interpretations.

¹Le Zhang,¹Cheng-Yuan Wang,²Hai-Yang Xian,¹Jintuan Wang,¹Yan-Qiang Zhang,³Zhian Bao,¹Mang Lin,¹Yi-Gang Xu
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.06.019]
¹State Key Laboratory of Isotope Geochemistry and CAS Centre for Excellence in Deep Earth Science Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
³State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China
Copyright Elsevier

Impact glasses are abundant in the lunar regolith, and Mg isotopes have the potential to trace components from various lunar crustal reservoirs, which have recently been shown to exhibit large Mg isotopic fractionations. However, it remains unclear whether Mg isotopic fractionation occurs during the formation of impact glasses. In this study, we report in situ Mg isotopic and elemental compositional data for agglutinatic glasses returned by the Chang’e 5 mission and obtained using the laser ablation split stream technique. Vesicular textures, Fe–Ni alloys, tiny Fe droplets, and high Ni contents suggest the studied agglutinatic glasses had an impact origin. The agglutinatic glasses exhibit large Mg isotopic fractionation, with δ26Mg values ranging from −1.36 ‰ to −0.01 ‰. The lack of correlations between δ26Mg values, Ni contents, and ratios between volatile and relatively refractory elements (K/La, Rb/Sr, and Ce/Pb) indicate the addition of a meteoritic component and evaporation was not the major process responsible for the measured Mg isotopic variations. In fact, the MgO profiles and correlations between δ26Mg and MgO, Na2O, Sc, Sr, CaO/Al2O3, and δEu reflect Mg isotopic fractionation caused by Mg diffusion from a region with high Mg contents (i.e., more melted pyroxene) to one with lower contents (i.e., more melted plagioclase). Diffusion modeling shows that the duration of diffusion was less than a fraction of a second. Our results indicate that chemical diffusion can produce large Mg isotopic fractionation in impact glasses on a scale of at least tens of microns, and that isotopic fractionation driven by chemical diffusion needs to be considered when the Mg isotopic compositions of impact glasses are used to identify different lunar rock reservoirs.