^1,2Zhuang Guo,¹Yu Zhu,^2,3Yang Li,⁴Ian M. Coulson,^2,3Xiongyao Li,^2,3Jianzhong Liu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14283]
¹State Key Laboratory of Continental Dynamics & NWU-HKU Joint Center of Earth and Planetary Sciences, Department of Geology, Northwest University, Xi’an, China
²Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
³Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, China
⁴Solid Earth Studies Laboratory, Department of Geology, University of Regina, Regina, Canada
Published by arrangement with John Wiley& Sons

Basaltic shergottites are the most abundant rock type of Martian meteorites, and pyroxene grains within shergottites commonly show a zoned structure. Here, the detailed microscopic mineralogical characteristics of patchy zoned pyroxene in basaltic shergottite NWA 12522 were investigated by a combination of scanning electron microscopy, electron microprobe, Raman spectroscopy, and transmission electron microscopy. The results show that the cores of zoned pyroxene in NWA 12522 have a homogeneous Mg# value and consist mainly of augite and pigeonite. By contrast, the rim of zoned pyroxene is extremely ferroan and can be further divided into two regions based on quite distinct mineralogy and textures (i.e., far-core and near-core pyroxene rims). The near-core rim shows narrow exsolution lamellae (~35 nm) that were cross-cut by thin pigeonite veinlets and contain abundant nano-sized particles of metastable pyroxferroite and pigeonite. Only relatively coarse exsolution lamellae (~80 nm) were observed in the far-core pyroxene rim regions. The distinct mineralogical characteristics of the pyroxene rims and cores in NWA 12522 imply different crystallization conditions, and the homogeneous Mg-rich pyroxene cores should have slowly crystallized from magma within a deep-seated chamber, followed by an overgrown evolved melt on these pyroxene cores during their ascent to the Martian surface, and disequilibrium crystallization of nano-sized metastable phase (pyroxferroite) occurred in the near-core region. The abnormally low ΣREE contents and steep REE pattern (high Yb/La ratio) of the pyroxene rims in NWA 12522 imply that merrillite should have crystallized prior to the pyroxene rims, making the residual melt become REE-depleted and HREE-enriched.

¹A. C. Stadermann,²T. M. Erickson,¹L. B. Seifert,³Y. Chang,³Z. Zeszut,³T. J. Zega,⁴Z. D. Michels,³J. J. Barnes
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14282]
¹NASA Johnson Space Center, Houston, Texas, USA
²Jacobs JETS Contract at NASA Johnson Space Center, Houston, Texas, USA
³Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
⁴Department of Geosciences, University of Arizona, Tucson, Arizona, USA
Published by arrangement with John Wiley & Sons

The temperature and pressure conditions experienced by rocks during an impact event can be constrained using petrologic and microstructural analysis and is crucial to providing ground truth to the impact cratering process. Suevite is a polymict, impact melt-bearing breccia, specific to Ries crater in Germany. There are competing models for suevite formation and emplacement, such as clastic flows pushed out of the crater rim or ejecta plume fallback. Knowledge of the temperature and pressure pathways recorded by grains within the suevite can help distinguish between these and other models. The accessory phase zircon (ZrSiO4) and its high-pressure polymorph reidite are particularly useful in such circumstances as they are highly refractory minerals that can record the high-temperature and/or high-pressure conditions of an impact event. Here, we present evidence for a wide array of temperature and pressure conditions recorded in zircon grains within a single thin section of suevite. Zircons in this study range from unshocked to highly shocked (>53 GPa), and record temperatures more than 1673°C. These findings confirm previous studies concluding that suevites contain material exposed to very diverse pressure and temperature conditions during initial shock compression and excavation but do not, as a whole, experience extreme temperatures (>1673°C) or pressures (>30 GPa).

^1,2Alan E. Rubin
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14284]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, USA
²Maine Mineral & Gem Museum, Bethel, Maine, USA
Published by arrangement with John Wiley & Sons

H, L, and LL chondrites all exhibit positive correlations between mean shock stage and petrologic type. At a given shock energy, hot samples exhibit more intense shock features than cold samples. After the ordinary-chondrite (OC) parent asteroids were collisionally disrupted, jumbled, and gravitationally reassembled, the correlations between mean shock stage and petrologic type may have resulted from stochastic collisions into material of different temperatures that were randomly distributed in the near-surface regions of the rubble-pile asteroids. Late-stage processes including shock events and post-shock annealing affected the preexisting correlations to only minor degrees. This model, combined with literature data, permits the following scenario: Each principal OC asteroid initially had an onion-shell structure with deeply buried type 6 materials cooling slowly, yielding young closure ages in Pb-phosphate data. The OC bodies were disrupted at ~60 Ma, locking in the Pb-phosphate record of the onion-shell structure. The H-chondrite parent body was collisionally disrupted somewhat later than the L or LL bodies and was thus somewhat cooler at the time of disruption. In the OC asteroidal rubble piles, materials of different petrologic types cooled at similar rates through ~500°C, precluding a correlation between petrologic type and metallographic cooling rate. Shortly after rubble-pile formation, materials of higher petrologic types remained hotter than materials of lower petrologic types. The hotter materials recorded more intense shock features from the common meteoroid flux, leading to positive correlations in each OC asteroid between petrologic type and mean shock stage. The cooler H-chondrite materials manifested a lower range in mean shock stage.

¹C. Alwmark,²G. G. Kenny,¹S. Alwmark,³P. Minde,⁴J. Plado,⁴S. Hietala, ², M. J. Whitehouse
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14280]
¹Department of Geology, Lund University, Lund, Sweden
²Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden
³Arctic Planetary Science Institute, Rovaniemi, Finland
⁴Department of Geology, Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia
⁵Geological Survey of Finland, Kuopio, Finland
Published by arrangement with John Wiley & Sons

Here we report on findings for four rock samples with melt texture found in a gravel pit within a glaciofluvial deposit near the small town of Kitkiöjärvi in northernmost Sweden. The samples are comprised of granitic clasts embedded in a brown fine-grained melt matrix. The samples all contain quartz grains and/or clasts exhibiting multiple sets of planar deformation features oriented parallel to crystallographic planes characteristic of shock metamorphism. The samples also contain Former Reidite In Granular Neoblastic (FRIGN) zircon. We therefore conclude that the investigated samples represent impact melt rock. We interpret a U-Pb concordia age of 658.9 ± 6.9 Ma (Cryogenian) derived using secondary-ion mass spectrometry analysis of shocked zircon, as the best estimate for the age of the impact event that formed the melt rocks. Zircon grains from two of the samples yield younger lower intercept ages, raising the possibility that the samples came from multiple impact events of different ages. Although we cannot exclude this possibility, we interpret the younger ages from the clast-rich melt rocks to reflect non-impact-related Pb loss events and suggest that all samples likely came from the same structure. Analysis of the glaciofluvial history of the region, along with the relatively high frequency of finds (five in total, as one similar melt rock was found in the pit in 2018), points to a short-distance glacial transportation of the samples from the southwest. Since there are no known impact structures in Sweden within that area and/or of similar age, we conclude that an old (the oldest known yet) impact structure in Sweden potentially is yet to be discovered somewhere in the vicinity of the gravel pit.

¹Roger L. Gibson,¹S’lindile S. Wela,^2,3Auriol S. P. Rae,¹Marco A. G. Andreoli
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14275]
¹School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
²Department of Earth Sciences, University of Cambridge, Cambridge, UK
³School of GeoSciences, University of Edinburgh, Edinburgh, UK
Published by arrangement with John Wiley & Sons

The 369 m deep M4 drill hole, located ~18 km NNW of the center of the 146 Ma Morokweng impact structure (MIS), intersects shocked Archean granitoid gneisses and subsidiary dolerite intrusions that are cut by faults, cataclasites and mm- to m-wide suevitic and pseudotachylitic breccia dikes. The shock features in quartz in the gneisses and breccia dikes include decorated planar deformation features (PDFs), planar fractures, feather features, and toasting. Other minerals show features that may be shock-related, such as multiple sets of planar features and alternate twin ladder structures in feldspars, kink bands in biotite, and planar features in titanite, apatite, and zircon; however, these are variably annealed and/or overprinted by hydrothermal alteration effects, and confirmation of their origin awaits further study. Universal Stage measurements of PDF sets in quartz from 12 gneissic target rocks and from lithic and mineral clasts in three suevitic and three pseudotachylitic breccia dikes reveal four dominant sets: (0001), {10⁢1¯⁢3}, {10⁢1¯⁢4} and {10⁢1¯⁢2}. Based on these observations, the average peak shock pressure in these rocks is estimated at ≤16 GPa, which supports the original proximity (within one transient cavity radius) of these rocks to the point of impact. No discernible depth-dependent shock attenuation was noted in the core. These shock levels and the elevated structural position of the rocks in the M4 core relative to the impact melt sheet intersected in drill holes closer to the center of the MIS suggest that the M4 lithologies represent part of the parautochthonous peak ring volume that subsequently experienced 1.5–2 km of post-impact erosion before it was buried beneath younger sediments. Numerical modeling using the iSALE-2D code suggests that the original Morokweng crater had a rim-to-rim diameter of between 70 and 80 km, and that the rocks in the M4 core were originally located at a depth of 7–8 km and a radial distance of 8–9 km from the point of impact.

^1,2Jan L. Hellmann, ^3,4Gerrit Budde, ¹Lori N. Willhite, ¹Richard J. Walker
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.10.027]
¹Department of Geology, University of Maryland, 8000 Regents Drive, College Park, MD 20742, United States
²Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
³Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook Street, Providence, RI 02912, United States
⁴Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
Copyright Elsevier

The short-lived 182Hf–182W system is widely used for constraining the chronology of the early Solar System, including the timing of the formation, thermal evolution, and differentiation of planetary bodies. Utilizing the full potential of the Hf–W system requires knowledge of the Hf/W ratio and W isotopic composition of primitive chondritic material. However, metal-silicate heterogeneity among chondritic samples can complicate accurately determining the Hf–W systematics of bulk chondrite parent bodies. Moreover, interpreting Hf–W data for chondrites may be complicated by potential nucleosynthetic W isotope anomalies. To this end, we report Hf/W ratios and W isotope compositions for bulk ordinary and enstatite chondrites, as well as the first such data for Rumuruti chondrites. We find that ordinary and Rumuruti chondrites show no resolvable nucleosynthetic anomalies, whereas resolved ε183W (i.e., 0.01 % deviation in 183W/184W from terrestrial standard) excesses in individual enstatite chondrites suggest the presence of nucleosynthetic W isotope anomalies in bulk meteorite samples originating in the inner Solar System. These anomalies necessitate corrections when accurately quantifying radiogenic 182W variations. Furthermore, several ordinary chondrites deviate in Hf/W ratios and W composition from the parent body compositions previously obtained from internal 182Hf–182W isochrons, indicating variations in the abundance of metal across different chondrite samples. Similarly, the Hf–W systematics of some enstatite chondrites also deviate from the parent body values, which can be attributed to the heterogeneous distribution of Hf carrier phases. The new observations highlight the challenges in obtaining Hf-W data that are representative of the chondrite parent bodies from individual chondrites, especially from metal-rich samples. By contrast, Rumuruti chondrites of variable petrologic types exhibit uniform Hf/W and 182W/184W ratios, suggesting that these samples are representative of their parent body. Whereas their Hf/W ratio is similar to that of carbonaceous chondrites, their W isotope composition is less radiogenic. This indicates that the Rumuruti precursor reservoir most likely had a significantly lower Hf/W ratio than the ratio measured in Rumuruti chondrites today. These findings underscore the importance of understanding the likely variations in Hf-W isotope systematics of iron meteorite parent bodies for accurately determining the timing of core formation.

^1,2K.R. Bermingham , ^1,2H.A. Tornabene , ²R.J. Walker , ¹L.V. Godfrey , ³B.S. Meyer , ²P. Piccoli , ^4,5,6,7S.J. Mojzsis
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.11.005]
¹Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854 USA
²Department of Geology, University of Maryland, College Park, MD 20742 USA
³Department of Physics and Astronomy, Clemson University, Clemson NC 29631 USA
⁴HUN-REN, Research Centre for Astronomy and Earth Sciences (CSsFK), MTA Centre for Excellence, 1121 Budapest, Hungary
⁵Department of Lithospheric Research, University of Vienna, UZA 2, Josef-Holaubek-Platz 2, 1090 Vienna, Austria
⁶Department of Geosciences, Centre for Planetary Habitability (PHAB), University of Oslo, Postboks 1028 Blindern 0316 Oslo, Norway
⁷Institute for Earth Sciences, Friedrich-Schiller University, Burgweg 11, 07749 Jena, Germany
Copyright Elsevier

Constraining the origin of Earth’s building blocks requires knowledge of the chemical and isotopic characteristics of the source region(s) where these materials accreted. The siderophile elements Mo and Ru are well suited to investigating the mass-independent nucleosynthetic (i.e., “genetic”) signatures of material that contributed to the latter stages of Earth’s formation. Studies contrasting the Mo and Ru isotopic compositions of the bulk silicate Earth (BSE) to genetic signatures of meteorites, however, have reported conflicting estimates of the proportions of the non-carbonaceous type or NC (presumptive inner Solar System origin) and carbonaceous chondrite type or CC (presumptive outer Solar System origin) materials delivered to Earth during late-stage accretion (likely including the Moon-forming event and onwards). The present study reports new mass-independent isotopic data for Mo, which are presumed to reflect the composition of the BSE. A comparison of the new estimate for the BSE composition with new data for a select suite of NC iron meteorites is used to constrain the genetic characteristics of materials accreted to Earth during late-stage accretion. Results indicate that the final 10 to 20 wt% of Earth’s accretion was dominated by NC materials that were likely sourced from the inner Solar System, although the addition of minor proportions of CC materials, as has been suggested to occur during accretion of the final 0.5 to 1 wt% of Earth’s mass, remains possible. If this interpretation is correct, it brings estimates of the genetic signatures of Mo and Ru during the final 10 to 20 wt% of Earth accretion into concordance.

¹S. Chakraborty, ²B. Raychaudhuri, ³T. Pratim Das, ⁴S. Das, ¹M. Roy
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116365]
¹Narula Institute of Technology, West Bengal, India
²Presidency University, West Bengal, India
³Science Program Office, ISRO Headquarters, Bangalore, India
⁴Indian Institute of Technology, Indore, India
Copyright Elsevier

This work reports the spatial and diurnal variations of the number densities of lunar molecular water (H2O), atomic mass unit (amu) 18 and hydroxyl (OH), amu 17 over low (0° to 30°), middle (31° to 60°) and high (61° to 80°) latitudinal regions of the lunar exosphere during the pre-sunrise, noon, sunset and midnight periods using the mass spectrometric data of CHandra’s Atmospheric Composition Explorer-2 (CHACE-2) on board Chandrayaan-2, the second lunar mission developed in India. Both H2O and OH exhibit, particularly in the low latitude regions, a trend of increasing number density after the sunrise and up to noon, followed by a decrease till sunset. An overall higher density of H2O is obtained compared to the previous reports. The findings are justified in terms of the polar orbital height of the instrument and the duration of data procurement. The maximum number density for the low, middle and high latitudes reaches 5225 cm−3, 5135 cm−3 and 3747 cm−3, respectively. The corresponding OH abundances are found to be 5079 cm−3, 5565 cm−3 and 5720 cm−3. The diurnal variations of H2O and OH and their comparisons, similar to those of the present report may provide suitable means for tracing the lunar water cycle. The CHACE-2 observations imply that the influence of magnetotail passage on volatiles like water is to be further quantified in future missions with other sensors.

¹Xiao-Wen Liu, ^1,2Ai-Cheng Zhang, ³Li-Hui Chen, ¹Lang Zhang, ³Xiao-Jun Wang, ^2,4Jia Liu, ^2,4Li-Ping Qin, ⁵Yu Liu, ⁵Qiu-Li Li, ⁵Xiao-Xiao Ling
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.11.004]
¹State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
²CAS Center for Excellence in Comparative Planetary, Hefei 230026, China
³State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China
⁴CAS Key Laboratory of Crust-Mantle Materials and Environment, University of Science and Technology of China, Hefei 230026, China
⁵State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Copyright Elsevier

Understanding of the diversity and petrogenesis of achondrites is critical for deciphering magmatic processes and the early evolution of planets and asteroids. Here, we report the detailed petrologic, mineralogical, geochemical, and chronological features of the unbrecciated Vestan meteorite Northwest Africa (NWA) 8326. We found that NWA 8326 is composed of coarse-grained orthopyroxene (∼74 vol%), plagioclase (∼19 vol%), fine-grained augite (∼5 vol%), and many accessory minerals such as chromite, ilmenite, Fe-sulfide, silica phases, K-feldspar, Ca-phosphate phases, zircon, baddeleyite, rutile, and primary Si,Al,K-rich glass, differing from typical howardite-eucrite-diogenite meteorites. Based on textural feature and compositional calculation of pyroxene, we suggest that the coarse-grained orthopyroxene was inverted from primary pigeonite and NWA 8326 should be classified as a pigeonite cumulate eucrite. The oxygen and chromium isotope data (Δ¹⁷O =  − 0.254 ± 0.009 ‰; ε⁵⁴Cr =  − 0.60 ± 0.06) support this classification. A few zircon aggregates are observed in NWA 8326 and the grains therein show a core-mantle zoned texture in cathodoluminescence (CL) images, with the cores being dark and Al-rich while the mantles being bright and Al-poor. We interpret that the CL-dark cores are xenocrystic zircon grains derived from eucrites, whose presence indicates that NWA 8326 should have formed through partial melting of the Vestan mantle, with assimilation of eucritic material. The presence of xenocrystic zircon and primary Si,Al,K-rich glass and the large compositional variation of plagioclase indicate that NWA 8326 is an unequilibrated cumulate eucrite and hence the zircon ²⁰⁷Pb/²⁰⁶Pb age of 4559.2 ± 5.2 (2σ) Ma represents the crystallization of NWA 8326. Reconciling the cumulative texture with the presence of the chemically evolved glass, NWA 8326 would be excavated during the late stage of its crystallization and escaped the prevalent crustal thermal metamorphism of the eucrite parent body. The Mg isotopic composition of NWA 8326 is higher than most diogenites, which suggests that the parent magma of such a pigeonite cumulate eucrite was derived from a source region with heavier magnesium isotopic composition (μ²⁵Mg: −90 to − 96 ppm).

¹Chi Ma,²Alexander N. Krot,²Kazuhide Nagashima,³Tasha Dunn
The American Mineralogist 109, 2006-2012 Link to Article [https://doi.org/10.2138/am-2023-9283]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawaii 96822, U.S.A.
³Department of Geology, Colby College, Waterville, Maine 04901, U.S.A.
Copyright: The Mineralogical Society of America

Louisfuchsite (IMA 2022-024), with an end-member formula Ca₂(Mg₄Ti₂)(Al₄Si₂)O₂₀, is a new refractory mineral identified in a Ca-Al-rich inclusion (CAI) from the NWA 4964 CK3.8 carbonaceous chondrite. Louisfuchsite occurs with spinel, perovskite, grossmanite, plus secondary rutile, titanite, and ilmenite in three regions in the CAI. The mean chemical composition of type louisfuchsite by electron probe microanalysis is (wt%) Al₂O₃ 25.48, SiO₂ 18.40, MgO 17.92, TiO₂ 15.36, Ti₂O₃ 3.13, CaO 14.92, FeO 3.30, V₂O₃ 0.67, Cr₂O₃ 0.08, total 99.26, giving rise to an empirical formula of Ca_2.00(Mg_3.44Ti1.494+Fe_0.36Ti0.343+Al_0.24V0.073+Ca_0.06Cr_0.01)_Σ6.01(Al_3.63Si_2.37)_Σ6.00O₂₀. Louisfuchsite has the P1 rhönite structure with a = 10.37(1) Å, b = 10.76(1) Å, c = 8.90(1) Å, α = 106.0(1)°, β = 96.0(1)°, γ = 124.7(1)°, V = 741(2) ų, and Z = 2, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.44 g/cm³. Louisfuchsite is a new refractory phase from the solar nebula, crystallized from an ¹⁶O-rich (Δ¹⁷O ~ −24 ± 2‰) refractory melt with the initial ²⁶Al/²⁷Al ratio of (5.09 ± 0.58) × 10⁻⁵ under reduced conditions. The mineral name is in honor of Louis Fuchs (1915−1991), a mineralogist at Argonne National Laboratory, for his many contributions to mineralogical research on meteorites.