^1,2,3Yuri Amelin, ⁴Qing-Zhu Yin, ^2,5Piers Koefoed, ^2,6Renaud Merle, ^7,8Yuki Hibiya, ^4,9Magdalena H. Huyskens, ⁷Tsuyoshi Iizuka, ¹⁰Julia A. Cartwright
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.11.008]
¹Research School of Earth Sciences, The Australian National University, Australia
²Division of Earth and Environmental Sciences, Korea Basic Science Institute, Ochang, 28119, South Korea
³State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry CAS, Guangzhou, 510640, China
⁴Department of Earth and Planetary Sciences, University of California-Davis, Davis, CA 95616, USA
⁵Department of Earth, Environmental, and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, MO, USA
⁶Department of Earth Sciences, Uppsala University, Villavägen 16, 75236 Uppsala, Sweden
⁷Department of Earth and Planetary Science, The University of Tokyo, Japan
⁸Research Center for Advanced Science and Technology, The University of Tokyo, Japan
⁹Geological Survey of Norway, Leiv Eirikssons vei 39, 7040 Trondheim, Norway
¹⁰Institute for Space, University of Leicester, UK
Copyright Elsevier

In this study we test the possibility that radiogenic 207Pb/206Pb ratios (207Pb*/206Pb*) in meteorites can be fractionated during partial dissolution, and explore the consequences of this fractionation for Pb-isotope chronology of meteorites. We report the results of experiments tailored to detect Pb-isotope fractionation, induced by partial dissolution through acid leaching, in plutonic angrite Northwest Africa (NWA) 4801 and ungrouped achondrites NWA 10132 and Erg Chech (EC) 002. We also re-examine previously published U-Pb data for other achondrites and for Ca-Al-rich refractory inclusions (CAIs), to seek evidence of such fractionation. We observe that, in primitive achondrite NWA 10132, differences in 207Pb*/206Pb* ratios, corresponding to the age bias of ca. 1–2 Ma, exist between the 0.5 M hydrofluoric acid leachates of pyroxene or crushed rock, and the residues after such leaching. In angrite NWA 4801, similar acid treatment of pyroxene separates did not cause a resolvable age bias. In EC 002, three steps of partial dissolution in 0.2 M – 5 M HF caused irregular 207Pb*/206Pb* fractionation between leaching steps, and generally higher 207Pb*/206Pb* ratios in the residues than in HF leachates. These age biases were observed in leaching pairs with highly radiogenic Pb, and cannot be explained by mixing between radiogenic Pb, primordial Pb, and Pb introduced by terrestrial contamination. Instead, the observed isotope fractionation is attributed to the combined effects of the size difference between α-recoil tracks in the decay chains of 238U and 235U, and exsolution of primary pigeonite, leading to the formation of a lamellar structure consisting of augite and low-Ca pyroxene by either slow-cooling or subsequent metamorphic reactions. Where extensive acid leaching intended for removal of non-radiogenic Pb causes fractionation of radiogenic Pb isotopes, its detrimental effect can be reversed by performing a numeric recombination of partial leachate and residue data. Currently, it is unclear how common leaching-induced isotopic fractionation is in Pb-isotopic chronology to meteoritic materials. Acid leaching is an essential step for removal of non-radiogenic Pb in the precise Pb-isotopic dating of meteorites, which currently does not have viable alternatives. However, it is important to be aware of its possible side effects, and to continue search for new non-radiogenic Pb removal techniques that do not cause radiogenic 207Pb* and 206Pb* fractionation.

^1,2Zhipeng Xia,^1,2Baochen Yang,^1,2Bowen Si,^1,2Guozhu Chen,^1,2Xi Wang,^1,3Hongyi Chen,^1,2Chuantong Zhang,^1,2Bingkui Miao
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14285]
¹Institution of Meteorites and Planetary Materials Research, Key Laboratory of Planetary Geological Evolution, Guilin University of Technology, Education Department of Guangxi Zhuang Autonomous Region, Guilin, China
²Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin, China
³Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources in Guangxi, Guilin University of Technology, Guilin, China
Published by arrangement with John Wiley & Sons

We present petrology and mineralogy for two lunar granulitic breccia meteorites that were detected in Northwest Africa (NWA), the samples NWA 15062 and NWA 15063. The fragments primarily consist of plagioclase and olivine mineral clasts, with minor amounts of anorthosite clasts and one troctolite clast. The anorthosite clasts are dominated by plagioclase/maskelynite, with minor olivine and pyroxene. A troctolite clast, composed of olivine and maskelynite, occurs in NWA 15063. The olivine clasts display mosaic extinction and usually have a homogeneous Mg-rich composition. However, all olivine mineral clasts exhibit two distinct ranges of their major element composition (Mg#: 85–88 and 77–78, respectively). Large individual plagioclase clasts show heterogeneous compositions (Ab content: 2.5–4.8) and have different Raman peak positions in different domains. The matrix of the meteorites appears semitransparent and is composed of olivine and pyroxene aggregates associated with maskelynite, constituting a granoblastic texture. Pyroxenes of the matrix are dominantly enstatites, associated with a few augites. Both meteorite samples exhibit shock-induced melt veins ranging from 50 to 200 μm width. These melt veins traverse the entire samples and contain rare, very fine-grained (2–3 μm) Mg-rich olivine clasts (Mg# = 90–93) and mafic silicate glass. Some Cr-spinel grains exhibit slight compositional zonation, characterized by a magnesium-rich core (Mg# = 56, Cr# = 23) and Cr-rich rims (Mg# = 50, Cr# = 28), with decomposition at the edges. The significantly differing Mg# contents of the mafic silicate minerals in the matrix, lithic clasts, and mineral clasts of the two meteorites indicate a diverse origin of the clasts. Based on their petrology, mineral chemistry, and bulk composition, NWA 15062 and NWA 15063 are classified as anorthositic troctolitic granulitic polymict breccia. Textural evidence suggests that the parent rocks of NWA 15062 and NWA 15063 were affected by high pressure of up to 30 GPa during impact-induced shock metamorphism, causing crystal structure deformation in olivine and the transformation of plagioclase to maskelynite. During cooling from peak temperatures of 1600–1700°C, the coarse-grained maskelynite mineral clasts were partially devitrified, and the granoblastic texture of the matrix was developed. Mg-rich anorthosite was formed before this shock event. Cr-spinel was formed in a troctolitic melt, which was probably differentiated after the crystallization of anorthite and magnesium-rich olivine. However, the possibility of the formation of the Mg-rich melt through interaction with the lunar anorthositic crust cannot be ruled out. The meteorite NWA 15062/15063 strongly resembles the textural, chemical, and mineralogical characteristics of the NWA 5744 meteorite group. Therefore, we interpret the two samples as a new member of the NWA 5744 meteorite group.

^1,2Chen Li et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.10.035]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
²Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
Copyright Elsevier

The formation of a unique microstructure of minerals on the surface of airless bodies is attributed to space weathering. However, it is difficult to distinguish the contributions of meteorite impacts and solar wind to the modification of lunar soil, resulting in limited research on the space weathering mechanism of airless bodies. The thermochemical reactivity of troilite can be used to distinguish the contributions of impact events and solar wind to the modification of lunar soil and provide evidence for space weathering of lunar soil. We examined the structure of a single particle of troilite in the Chang’e-5 lunar soil and determined whether an impact caused the thermal reaction. Microanalysis showed that troilite underwent substantial mass loss during thermal desulfurization, forming a crystallographically aligned porous structure with iron whiskers, an oxygen-rich layer, and other crystallographic and thermochemical evidence. We used an ab initio deep neural network model and thermodynamic calculations to conduct experiments and determine the anisotropy and crystal growth of troilite. The surface microstructure of troilite was transformed by the thermal reaction in the vacuum on the lunar surface. Similar structures have been found in near-Earth objects (NEOs), indicating that small bodies underwent the same impact-induced thermal events. Thus, thermal reactions in a vacuum are likely ubiquitous in the solar system and critical for space weathering alterations of the soil of airless bodies.

^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.