¹Paul H. Warren,²Junko Isa,¹Bidong Zhang,³Randy L. Korotev
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116144]
¹Department of Earth, Planetary and Space Science, UCLA, Los Angeles, CA 90095, USA
²Cold Pine Observatory, 201, 4-22, Matsugaoka 1-cho me, Chigasaki, Kanagawa, Japan
³Department of Earth, Environmental, and Planetary Sciences, Washington University, St. Louis, MO 63130, USA
Copyright Elsevier

According to several orbital reflectance spectroscopy studies, numerous widely scattered lunar surface locales feature remarkably high (>98%) abundance of plagioclase. These “pure” anorthosite claims are based on an absorption band at ~1.25 μm, associated with minor Fe2+ within plagioclase. But utilization of the 1.25 μm band as a direct gauge of plagioclase abundance requires an underlying assumption that plagioclase FeO is uniform across all measured materials. Available data for FeO in lunar plagioclase are in many cases suspect because electron-probe FeO measurements may be inflated by secondary fluorescence from nearby mafic phases. We studied plagioclase FeO in a set of 13 anorthositic lunar rocks, taking care to avoid proximity to mafic phases; or in cases where complete avoidance was not possible without sacrificing representativeness (i.e., fine-grained impact melt rocks with zoned silicates), correcting close-to-mafic analyses for secondary fluorescence (Sugawara, T. [2001], Japanese Mag. Mineral. Petrol. Sci. 30, 159–163). Results for rock-average plagioclase FeO range from 0.030 wt% in plutonic troctolitic anorthosite 76,335, to 0.23 wt% in impact-melt rock 14,310. In general, as shown by exsolution of mafic silicates from plagioclase within several samples, final plagioclase FeO in lunar plutonic anorthosites is determined by reequilibration during slow postigneous cooling and/or metamorphism. In contrast, four fast-cooled anorthositic impact melt rocks have consistently higher plagioclase FeO, averaging 1.9 times higher in comparison to average plutonic anorthositic rock. Thus, impact melted lunar anorthosite will have far more prominent 1.25 μm absorption than plutonic anorthosite of the same plagioclase abundance. In view of the inconstancy of plagioclase FeO, orbital spectral reflectance using the 1.25 μm absorption band, or the ratio between that band and one or more mafic silicate bands, cannot be precise enough to justify claims of ability to resolve “purest” (98 vol% +) anorthosite from compositions that are high-plagioclase but not that extreme.

¹Addi Bischoff et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14193]
¹Institut für Planetologie, University of Münster, Münster, Germany
Published by arrangement with John Wiley & Sons

Elmshorn fell April 25, 2023, about 30 km northwest of the city of Hamburg (Germany). Shortly after the fall, 21 pieces were recovered totaling a mass of 4277 g. Elmshorn is a polymict and anomalous H3-6 chondritic, fragmental breccia. The rock is a mixture of typical H chondrite lithologies and clasts of intermediate H/L (or L, based on magnetic properties) chondrite origin. In some of the 21 pieces, the H chondrite lithologies dominate, while in others the H/L (or L) chondrite components are prevalent. The H/L chondrite assignment of these components is based on the mean composition of their olivines in equilibrated type 4 fragments (~Fa21–22). The physical properties like density (3.34 g cm−3) and magnetic susceptibility (logχ <5.0, with χ in 10−9 m3 kg−1) are typical for L chondrites, which is inconsistent with the oxygen isotope compositions: all eight O isotope analyses from two different fragments clearly fall into the H chondrite field. Thus, the fragments found in the strewn field vary in mineralogy, mineral chemistry, and physical properties but not in O isotope characteristics. The sample most intensively studied belongs to the stones dominated by H chondrite lithologies. The chemical composition and nucleosynthetic Cr and Ti isotope data are typical for ordinary chondrites. The noble gases in Elmshorn represent a mixture between cosmogenic, radiogenic, and primordially trapped noble gases, while a solar wind component can be excluded. Because the chondritic rock of Elmshorn contains (a) H chondrite parent body interior materials (of types 5 and 6), (b) chondrite parent body near-surface materials (of types 3 and 4), (c) fragments of an H/L chondrite (dominant in many stones), (d) shock-darkened fragments, and (e) clasts of various types of impact melts but no solar wind-implanted noble gases, the different components cannot have been part of a parent body regolith. The most straightforward explanation is that the fragmental breccia of Elmshorn represents a reaccreted rock after a catastrophic collision between an H chondrite parent body and another body with H/L (or L) chondrite characteristics but with deviating O isotope values (i.e. that of H chondrites), complete disruption of the bodies, mixing, and reassembly. This is the only straightforward way that the implantation of solar wind gases could have been avoided in this kind of complex breccia. The gas retention ages of about 2.8 Gyr possibly indicate the closure time after the catastrophic collision between H and H/L (or L) chondrite parent bodies, while the cosmic ray exposure age for Elmshorn, which had a preatmospheric radius of 25–40 cm, is ~17–20 Myr.

¹I. Kouvatsis,^2,3J. A. Cartwright,¹W. E. Hames
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14219]
¹Department of Geological Sciences, University of Alabama, Tuscaloosa, Alabama, USA
²School of Physics and Astronomy, Institute for Space, University of Leicester, Leicester, UK
³Institute for Space, Space Park Leicester, University of Leicester, Leicester, UK
Published by arrangement with John Wiley & Sons

CM chondrites are samples from primitive water-rich asteroids that formed early in the solar system; many record evidence for silicate rock–liquid water interaction. Many CM chondrites also exhibit well-developed fine-grained rims (FGRs) that surround major components, including chondrules and refractory inclusions. Previous studies have shown that Aguas Zarcas, a CM2 chondrite fall recovered in 2019, is a breccia consisting of several lithologies. Here, we present a study of Aguas Zarcas using optical microscopy, scanning electron microscopy, and electron probe microanalysis, focusing on brecciation and aqueous alteration on the parent body. We observed two lithologies within our sample, separated by a distinct textural and chemical boundary. The first lithology has a higher chondrule abundance (“chondrule-rich”) and significantly larger FGRs compared to the second lithology (“chondrule-poor”), even for similarly sized chondrules. We observed clear compositional differences between the two lithologies and more multilayered FGRs in the chondrule-rich lithology. We determined that the chondrule-rich lithology is less altered (petrologic type 2.7–2.8) and displays larger FGRs to chondrule ratios compared to the more altered chondrule-poor lithology (petrologic type 2.5–2.6). These observations are contrary to previous models that predict aqueous alteration as a cause of FGR formation in the parent body. Our observed differences in Mg and Fe distribution in the lithology matrices alongside variable FGR thickness suggest distinct formation environments. We propose that the Aguas Zarcas parent body was subjected to several minor and major brecciation events that mixed different materials with variable degrees of aqueous alteration together, in agreement with previous studies.

¹N. Randazzo,¹R. W. Hilts,¹M. C. Holt,¹C. D. K. Herd,²B. Reiz,²R. M. Whittal
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14189]
¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
²Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
Published by arrangement with John Wiley & Sons

We analyzed the methanol extracts of six pristine specimens of the Tagish Lake meteorite (TL1, TL4, TL5A, TL6, TL7, and TL10a) and heated and unheated samples of Allende using high-performance liquid chromatography coupled with high-resolution, accurate mass–mass spectrometry (HPLC-HRAM-MS). All samples contained ppm levels of sulfate and methyl sulfate. The most abundant organosulfur compound in the methanol extracts of the Tagish Lake and Allende samples was methyl sulfate, which was likely formed primarily via an esterification reaction between intrinsic sources of methanol and sulfate. A homologous series of polythionic acids was also observed in the extracts of the Tagish Lake specimens and Allende. The polythionic acids were the most abundant soluble inorganic sulfur species found in the meteorites. Our results were confirmed using retention time, accurate mass, isotope matching, and tandem mass spectrometry (MS/MS). Hydroxymethanesulfonic acid, previously reported in Tagish Lake, was found only in an unheated Allende sample and in low abundance. Here, we propose possible sulfate formation pathways that begin with interstellar dimethyl sulfide, dimethyl disulfide, methyl sulfide, or methanethiol via cold, nebular processes within the interstellar medium and continue via MSA as an intermediary compound ending within planetary bodies with sulfate and methyl sulfate as the final products.

^1,2,3,4Maria Gritsevich et al.(>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14173]
¹Faculty of Science, University of Helsinki, Helsinki, Finland
²Swedish Institute of Space Physics (IRF), Kiruna, Sweden
³Finnish Fireball Network, Ursa Astronomical Association, Helsinki, Finland
⁴Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia
Published by arrangement with John Wiley & Sons

The discovery of the Ischgl meteorite unfolded in a captivating manner. In June 1976, a pristine meteorite stone weighing approximately 1 kg, fully covered with a fresh black fusion crust, was collected on a mountain road in the high-altitude Alpine environment. The recovery took place while clearing the remnants of a snow avalanche, 2 km northwest of the town of Ischgl in Austria. Subsequent to its retrieval, the specimen remained tucked away in the finder’s private residence without undergoing any scientific examination or identification until 2008, when it was brought to the University of Innsbruck. Upon evaluation, the sample was classified as a well-preserved LL6 chondrite, with a W0 weathering grade, implying a relatively short time between the meteorite fall and its retrieval. To investigate the potential connection between the Ischgl meteorite and a recorded fireball event, we have reviewed all documented fireballs ever photographed by German fireball camera stations. This examination led us to identify the fireball EN241170 observed in Germany by 10 different European Network stations on the night of November 23/24, 1970, as the most likely candidate. We employed state-of-the-art techniques to reconstruct the fireball’s trajectory and to reproduce both its luminous and dark flight phases in detail. We find that the determined strewn field and the generated heat map closely align with the recovery location of the Ischgl meteorite. Furthermore, the measured radionuclide data reported here indicate that the pre-atmospheric size of the Ischgl meteoroid is consistent with the mass estimate inferred from our deceleration analysis along the trajectory. Our findings strongly support the conclusion that the Ischgl meteorite originated from the EN241170 fireball, effectively establishing it as a confirmed meteorite fall. This discovery enables to determine, along with the physical properties, also the heliocentric orbit and cosmic history of the Ischgl meteorite.

^1,2Yuruo Shi et al. (>10)
Meteoritics & Planetary Science (in Press)Link to Article [https://doi.org/10.1111/maps.14192]
¹Key Laboratory of Gold Mineralization Processes and Resource Utilization, MNR, Shandong Provincial Key Laboratory of Metallogenic Geological Process and Resource Utilization, Shandong Institute of Geological Sciences, Jinan, China
²Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

We carried out a petrological, mineralogical, and geochemical study of fragmental and regolith breccia clasts separated from two Chang’e-5 (CE-5) soil samples, CE5C0000YJYX03501GP and CE5C0400, which provide an opportunity to investigate the compositional change of regolith at the landing site through time. Fragmental breccia CE-5-B3 contains a diverse range of basaltic clasts and basaltic mineral fragments, and some rare Mg-suite-like minerals. Regolith breccias CE-5-B006, CE-5-B007, CE-5-B010-08, CE-5-B010-09, CE-5-B011-07, and CE-5-B016-03 contain mare basaltic fragments, mare vitrophyric clasts, rare Mg-rich fragments possibly derived from the Mg-suite rocks, and impact-derived glass spherules. Pb-isotope data obtained for baddeleyite grains found both inside some of the basaltic clasts identified in breccia fragments and in the breccia matrices yield Pb/Pb dates similar to the 2 Ga crystallization age of the CE-5 basalt fragments, extracted directly from the soil sample. Seventy-four Pb isotope analyses of Ca-phosphate grains also indicate that the majority of these grains have Pb/Pb dates of 2 Ga, suggesting that they originate from the CE-5 basalts. In addition, a Pb–Pb isochron drawn through analyses of four Ca-phosphates in breccia CE5-B006 yielded an intercept corresponding to a date of 3871 ± 46 Ma, which is the best possible estimate of the formation age of these four grains. Electron probe microanalysis shows that the breccias contain components similar to CE-5 mare basalt fragments extracted directly from the soil sample, implying that the fragmental and regolith breccia fragments are mostly composed of material sourced from the underlying basalts. The general absence of impact melt breccia clasts, along with the general lack of Fe–Ni metal and absence of added meteoritic debris all suggest that the regolith at the CE-5 landing site is immature and dominated by material mixed together by small local impact cratering events. Trace element analyses show that the glass beads in the regolith breccias have a Th abundance of 4.06–5.28 μg g−1. This is similar to the Th content of the regolith above the Em4 unit at the landing site as measured from orbit, as well as the estimated bulk Th content of CE-5 basalts, suggesting that Th of the local regolith is predominantly sourced from the underlying mare basalts, without significant Th addition from Th-rich exotic clasts sourced from evolved lunar lithologies.

¹Chengyuan Wang,¹Yi-Gang Xu,¹Le Zhang,¹Zhiming Chen,¹Xiaoping Xia,¹Mang Lin,¹Feng Guo
Earth and Planetary Science Letters 693, 118770 Link to Article [https://doi.org/10.1016/j.epsl.2024.118770]
¹State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, PR China
Copyright Elsevier

The lunar magma ocean (LMO) hypothesis predicts that the uppermost mantle (∼60–100 km) is composed of ilmenite-bearing cumulate (IBC), which may have sunk deeply due to gravitational instability. However, the extent to which this process restructured the lunar mantle and influenced mare volcanism remains unclear. Here, we approach this issue by examining pyroxenes in Chang’E-5 (CE5) basalts and petrological modeling. We show that the low Mg# and negative anomalies in Ti and Ta of CE5 basalts cannot be produced by extensive fractionation of peridotite-derived low-Ti basalts, but were most likely formed through partial melting of a shallow (< 100 km) IBC pyroxenite source. This model is also applicable to the ∼3.0 Ga lunar basaltic meteorites. The increasing involvement of IBC sources in young lunar magmas, also revealed by the remote-sensing data, implies an inefficient gravitational restructuring process during the late LMO stage and provides new insights into the thermochemical state of the lunar interior.

¹Haijun Li,¹Huapei Wang,¹Chen Wen,^1,2Ting Cao,¹Jiabo Liu
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2023JE008112]
¹Paleomagnetism and Planetary Magnetism Laboratory, School of Geophysics and Geomatics, China University of Geosciences, Wuhan, China
²School of Earth Sciences, China University of Geosciences, Wuhan, China
Published by arrangement with John Wiley & Sons

Magnetic records from meteorites provide valuable information about the formation and evolution of the solar system and planets. The parent planetesimals of chondrites are typically considered to be undifferentiated based on their primary chemical composition and texture. However, recent paleomagnetic investigations of various chondrites indicate that they carry a primary remanence generated by a dynamo, suggesting partial differentiation of their parent planetesimals. The presence of a dynamo within the parent planetesimal of LL chondrites remains uncertain due to the ambiguous origin of the remanent magnetism. Here, we report petrographic, paleomagnetic, and rock magnetic properties for the novel LL6 chondrite NWA 14180. The high metamorphic temperature experienced by NWA 14180 could have removed the pre-accretionary remanence. The fusion crust baked-contact test suggests that NWA 14180 preserves primary magnetic information about its parent body. Alternating field demagnetization results from interior subsamples reveal distinct low- and medium-coercivity components that may represent a viscous remanent magnetization acquired in the geomagnetic field. No natural remanent magnetization was unblocked in the high coercivity range, implying that NWA 14180 cooled in zero-field conditions. Therefore, we suggest that the parent body of NWA 14180 did not have a dynamo. Furthermore, this result suggests that the LL chondrite parent planetesimal accreted later and was smaller in size than other chondrite classes.

^1,2Dongyang Huang,^1,3Julien Siebert,²Paolo Sossi,¹Edith Kubik,¹Guillaume Avice,²Motohiko Murakami
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.05.010]
¹Institut de Physique du Globe de Paris, 75005 Paris, France
²Institute of Geochemistry and Petrology, ETH Zürich, 8092 Zürich, Switzerland
³Institut Universitaire de France, 75005 Paris, France
Copyright Elsevier

Nitrogen (N) is the most abundant element in Earth’s atmosphere, but is extremely depleted in the silicate Earth. However, it is not clear whether core sequestration or early atmospheric loss was responsible for this depletion. Here we study the effect of core formation on the inventory of nitrogen using laser-heated diamond anvil cells. We find that, due to the simultaneous dissolution of oxygen in the metal, N becomes much less siderophile (iron-loving) at pressures and temperatures up to 104 GPa and 5000 K, a thermodynamic condition relevant to the bottom of the magma ocean in the aftermath of the moon-forming giant impact. Using a core-mantle-atmosphere coevolution model, we show that the impact-induced processes (core formation and/or atmospheric loss) are unlikely to account for the observed N anomaly, which is instead best explained by the accretion of mainly N-poor impactors. The terrestrial volatile pattern requires severe N depletion on precursor bodies, prior to their accretion to the proto-Earth.

¹D. J. Joswiak,¹D. E. Brownlee,²A. J. Westphal,²Z. Gainsforth,³M. Zhang,³N. T. Kita
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14187]
¹Department of Astronomy, University of Washington, Seattle, Washington, USA
²Space Sciences Laboratory, University of California, Berkeley, California, USA
³WiscSIMS, Department of Geoscience, University of Wisconsin–Madison, Madison, Wisconsin, USA
Published by arrangement with John Wiley & Sons

A literature compilation of 1136 low-Ca pyroxene compositions from chondrules from 12 primitive type 2–3 carbonaceous, ordinary and enstatite chondrite groups define unique regions on an Al2O3 and Cr2O3 diagram when compared to low-Ca pyroxenes from equilibrated type 4-6 chondrites. Measured compositions of 100 low-Ca pyroxenes from comet Wild 2 and a giant cluster IDP of probable cometary origin are similar to each other and fall in the type 2–3 chondrite chondrule region suggesting that most of the pyroxenes likely formed in the solar nebula like conventional chondrules. The data imply that most low Ca-pyroxenes from comet Wild 2 and the giant cluster IDP formed from igneous crystallization processes and did not experience significant thermal metamorphism, indicating that the low-Ca pyroxenes were unlikely incorporated into large parent bodies prior to accretion in their respective comet bodies. An intriguing group of nine low-Ca pyroxenes from comet Wild 2 with low Cr and Al that fall where type 4–6 chondrites are located are interpreted as products of condensation. The compositional data combined with previously measured oxygen isotopes on 17 low-Ca pyroxenes support earlier conclusions that comet samples have links with carbonaceous, ordinary, and possibly enstatite chondrite groups. Our results provide additional evidence that comets accreted materials from multiple chondrule reservoirs throughout the solar nebula.