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The behaviors of radiogenic Pb in Zr-minerals are critical for reconstructing the chronological framework for the evolutionary history of our Earth and other planetary bodies. Previous investigations have revealed the presence of Pb nanograins in some terrestrial zircons and attributed it to radiation decay of U and mobilization and accumulation in zircon and a subsequent thermal metamorphic event. However, whether impact, a ubiquitous and fundamental process for the evolution of materials on planetary surfaces, can directly produce Pb nanograins in Zr-minerals remains unknown. Here, we report the discovery of abundant metallic Pb nanograins in zirconolite polycrystalline aggregates in the brecciated lunar meteorite Northwest Africa 8182. We propose that the metallic Pb nanograins and their host zirconolite polycrystalline aggregates formed during shock lithification of the host meteorite, which had a significant impact on micro-scale U-Pb isotopic chronology of shocked Zr-minerals. The formation of metallic Pb nanograins also indicates that a reduction of PbO took place during shock metamorphism. [ABSTRACT FROM AUTHOR]

Sulfides are accessory phases in lunar rocks but are important for understanding lunar interior processes as well as impacts on the lunar surface. Whether or not the lunar mantle had achieved sulfide saturation during magma ocean evolution and displays homogeneous sulfur isotopes remains under debate. The Chang'e-5 (CE-5) mission returned young (2.0 Ga) basalts from a mare terrain in the northern Oceanus Procellarum. Here we study chemical and sulfur isotopic compositions (δ34S V-CDT) of sulfides from CE-5 basaltic fragments and combine them with δ34S of other young (3.1–3.0 Ga) lunar low-Ti basalt (NWA 10597 and NWA 4734) and gabbro meteorites (NWA 6950) to compare them with Apollo low-Ti and high-Ti mare basalts. The sulfides in basaltic fragments of CE-5 are troilites (FeS) with low abundances of Ni, Co, and Cu (e.g., Ni < 0.04 wt% and Ni/Co < 0.3). Textures and chemical compositions indicate that most troilites are late-stage crystallization products from the highly evolved CE-5 basalts. Several troilites occur in the matrices of impactite clasts and are intergrown with Fe–Ni metal (12–36 wt% Ni, Ni/Co of 12–39). These troilites are distinct from the major population of troilites with noticeably higher Ni abundances (mostly > 0.2 wt% with Ni/Co of 1–3) and reconcile with the addition of meteoritic materials into the impact melts. The δ34S V-CDT of large troilite grains (>10 μm) from the CE-5 basaltic fragments and lunar meteorites were obtained by high-precision, high-spatial-resolution femtosecond laser ablation MC-ICP-MS which achieved external uncertainty (0.65 ‰, 2SD at 8-μm laser spots) like nano-SIMS. Sulfur degassing during surficial effusive lava flow likely led to a slight decrease in δ34S (by ∼ 1 ‰) for some basaltic fragments; however, such effects were limited to the scale of bulk rock samples, consistent with previous results. The mean δ34S of troilites in CE-5 basaltic fragments (0.35 ± 0.25 ‰, 2SE, n = 45) is similar to those of ancient (3.8–3.1 Ga old) Apollo low-Ti and high-Ti mare basalts and the young gabbro cumulate NWA 6950 (0.56 ± 0.21 ‰, 2SE, n = 10). The paired NWA 10597 and NWA 4734 show consistent δ34S, lower than most values by ∼ 0.5 ‰. Current data thus indicate that most mantle sources of lunar basalts would be homogeneous for δ34S (0.6 ± 0.3 ‰) and minor regions may be different. The overall homogenous δ34S from different mantle sources with variably low sulfur contents supports sulfide-undersaturated accumulation of the lunar magma ocean, which was inherited from strong volatile loss and evaporative fractionation during the formation of the Moon. [ABSTRACT FROM AUTHOR]

Pink spinel anorthosite (PSA) and pink spinel troctolite (PST) are two lunar lithologies known to contain Mg-rich spinel. PSA rich in spinel and lacking mafic minerals, was detected by the visible and near-infrared reflectance spectroscopy. PST clasts were found in returned lunar samples and meteorites. NWA 13191 is a recently approved lunar meteorite that contains a large amount of spinel-bearing clasts and provides an opportunity to discuss its origin. Sixty-four spinel-bearing clasts were studied in this research. These clasts are dominated by anorthitic feldspars (20.8–80.9 vol%, An90.9–96.8), mafic-rich and aluminum-rich glass (14.7–72.1 vol%) quenched from a melt, and spinels (0.19–5.18 vol%). Forty-nine of these clasts appear to have unusually low modal abundances of mafic silicates (avg. olivine ± pyroxene, 1.87 vol%), which distinguishes them from known spinel-bearing lunar samples (e.g., PST). The spinel compositions (avg. Mg# = 90.6, Al# = 97.4) and mafic minerals contents are basically consistent with those of PSA. The absorption characteristics of glass in the reflection spectrum are not obvious, so it is not clear if the PSA contains melt. The simulated crystallization experiment clearly shows that it contains a large amount of melt at the spinel crystallization stage. These phenomena provide experimental and sample evidence for the existence of glass in the lunar spinel-bearing lithologies. NWA 13191 records the highest known bulk Mg# (avg. 89.8), and the spinel records the highest Al# (98.8) and Mg# (93.1) of lunar samples to date. The chemical properties of spinel-bearing clasts in NWA 13191 are consistent with the slightly REE-enriched and alkali-poor Mg-suite rocks, such as PST, magnesian anorthosites (MANs), and olivine-enriched Mg-suite rocks. These phenomena and previous simulated crystallization experiments indicate that a Mg-Al-rich melt may be produced by impact melting of Mg-rich anorthosite precursors. The spinel is a metastable crystallization product along with plagioclase and vitric melt near the Moon's surface. This realization provides observational evidence for previous simulated crystallization experiments and theoretical speculations. [ABSTRACT FROM AUTHOR]

Shock lithification of regolith breccias is a ubiquitous process on the surfaces of airless planetary bodies and may induce thermal effects, including melting on regolith breccia minerals. However, potential thermal effects on lithic and mineral clasts in regolith breccias have seldom been quantitatively constrained. Here, we report two types of micro-textures of armalcolite [(Mg,Fe2+)Ti2O5] in an Mg-suite lithic clast from lunar regolith breccia meteorite Northwest Africa 8182. One type of armalcolite contains oriented fine-grained ilmenite grains; the other occurs as an aggregate of ilmenite, rutile, spinel, and loveringite. We propose that the two types of micro-textures formed through subsolidus breakdown of armalcolite by different processes. The formation of ilmenite inclusions in armalcolite is related to slow cooling after the solidification of its source rock, whereas the ilmenite-rutile-spinel-loveringite aggregates probably formed during the shock lithification event of NWA 8182. The results indicate that the temperature at the margin of lithic clasts could be raised up to at least 600 °C during strong shock lithification of lunar regolith and has profound thermal effects on the mineralogical and isotopic behaviors of lithic and mineral fragments in lunar regolith breccias. [ABSTRACT FROM AUTHOR]

The Mg‐spinel‐bearing rocks are an essential component of the lunar crust. They are widely distributed on the Moon's near and far sides. The study of petrogenesis provides a rare opportunity to understand the early lunar crust‐mantle interaction. Northwest Africa 12279 is a unique Mg‐spinel‐bearing troctolitic anorthosite lunar meteorite that is unbrecciated and pristine. The modal content of the spinel‐bearing troctolitic component is ∼95%. Five hundred sixty spinels larger than 100 μm are investigated in this paper, and 38 of them are found to contain magma melt inclusions. These magma melt inclusions represent the mixed composition between mantle melt and crust material during the crystallization of a spinel. They generally show an immiscible liquid phase separation, which can be divided into a magnesium‐rich and silica‐rich phase. The former is similar in chemical composition to the lunar mantle's peridotite or plutonic ultramafic Mg‐suite. The mantle melt reacts successively with Ferroan Anorthosites in the crust to crystallize Mg‐spinel, plagioclase, olivine, pyroxene, and silica phases. The large grains of euhedral Mg‐spinels with homogeneous chemical composition indicate they are the products of equilibrium crystallization, while plagioclase, olivine, pyroxene, and silica phase are the products of differentiated crystallization of mixed magma. This reaction may represent a typical process of lunar Mg‐suite. This work is the first to find petrological evidence that the melt from the lunar mantle intrudes into the crust and then undergoes a liquid phase immiscible separation to form the Mg‐spinel‐bearing troctolitic anorthosite. Plain Language Summary: Northwest Africa 12279 (weight 1,830 g) is the only known pristine and unbrecciated lunar spinel‐bearing troctolitic anorthosite, including lunar meteorites and returned samples. These pristine samples are indispensable for understanding Moon's history and chemical evolution. The spinel‐bearing rocks are an essential component of the lunar crust. They are widely distributed on the Moon's near and far sides. The study of petrogenesis provides a rare opportunity to understand the early lunar crust‐mantle interaction. Five hundred sixty spinels larger than 100 μm are investigated in three polished thin sections, and 38 contained magma melt inclusions. These magmatic inclusions represent the mixed composition between early mantle melt and crust material during the crystallization of a spinel. This work is the first to find evidence that the melt from the lunar mantle intrudes into the crust. The magnesium‐rich melt from the mantle assimilates with ferroan anorthosite (an igneous rock is composed of >90 vol.% plagioclase rich in calcium with minor iron‐rich pyroxene and olivine) from the early crust to form an Mg‐spinel‐bearing hypabyssal igneous rock. Key Points: Northwest Africa (NWA) 12279 is a unique lunar meteorite that is both unbrecciated and pristineThe magmatic melt inclusion in Mg‐spinel represents the mixed composition between lunar mantle melt and anorthositic crustThe formation of Mg‐spinel in NWA 12279 results from the interaction between the mantle material and the anorthositic crust of the Moon [ABSTRACT FROM AUTHOR]

Standard-size samples are usually used for traditional paleomagnetic studies. In some cases, small irregular samples are employed considering their amount and magnetic strength as well as experiment efficiency. With the development of deep space exploration, the demand for studying small and magnetic weak samples is increasing. In this study, we established a magnetic measurement technique for small rare samples. We designed low-background, sample-nondestructive and high-flexibility holders with various materials for different measurements of small samples. With the customized holders, we estimated uncertainty and reliability of magnetic measurements of small specimens from a terrestrial basalt. The results indicate that susceptibility and remanence of small specimens (e.g., 2-mm cubes) are more affected by measurement position than larger specimens (≥5 mm), which reminds us to pay special attention to consistency of the small specimen position during series of measurements. Moreover, susceptibility and remanence of small sister specimens (2-mm and 5-mm cubes) are more scattered than those of large ones (cube length ≥1 cm), mainly due to inhomogeneity of magnetic mineral abundance in the sample. Nevertheless, the average magnetic results of different-size specimens are generally consistent within error, indicating the inhomogeneity of small specimens can be averaged out and demonstrating the reliability of small samples during magnetic measurements. Finally, we tested our measurement system with a lunar meteorite, which mimics the Chang’e-5 returned samples in both size and mineralogy. The main minerals of the meteorite are plagioclase, pyroxene, troilite and kamacite. The isothermal remanent magnetization normalized paleointensity method recovered the expected laboratory field while the anhysteretic remanent magnetization corrected paleointensities are about 2-3 times the expected field, where the latter can be explained by inapplicability of the empirical f′ to the meteorite specimens. The anhysteretic remanent magnetization and IRM paleointensity calibration factor f′ and a of the lunar meteorite were calculated to be 3.89 and 3138 μT, respectively, which provides new constraints for the empirical values. The magnetic results of the lunar meteorite demonstrate the utility of our measurement system for small weak samples. This study provides technical support for paleomagnetic study of the Chang’e-5 and other extraterrestrial samples in the future.

A detailed petrological and mineralogical study of lunar meteorite NWA 11801 has found 24 glasses, nine of which have similar compositions. The chemical composition of nine glasses are similar, and their elements (for example major elements of Mg, Al, Ca, Fe and trace elements of Mn, Cr, etc) are distributed in a small area. They have MgO/ Al2O3 = 1. 31-1. 54, which falls in a range of lunar volcanic glasses (MgO/ Al2O3 >1. 25), so nine glasses are volcanic glasses. However, they have certainly discrepancy in the structure, the number and morphology of the internal microcrystals of volcanic glasses, these differences are caused by different cooling environment. Therefore, the features of structure and composition of nine volcanic glasses indicate that they may be from the same source of magma eruption and form in the different cooling environment. In addition, olivine phenocrysts are found in a volcanic glass. The olivines are euhedral with a high Fo value (76. 4 mol%-78. 2 mol%), indicating that olivines come from the interior of the moon and record the crystallization and evolution of lunar magma. [ABSTRACT FROM AUTHOR]

In this study, we investigate the mineralogical and petrochemical characteristics of maskelynite occurring in a shocked basalt boulder from a terrestrial impact crater on a basaltic target – the Lonar impact crater in India, and the martian and lunar meteorites. The majority of Lonar maskelynite experienced solid-state transformation and maintained almost a uniform chemical composition, consistent with the unshocked feldspar. The locally flow-like texture and marginal vesiculation in feldspathic glass are needed in interaction with the impact-melt. The vesiculated melt occasionally occurring at the margins of maskelynite is characterised by Na-loss due to the shock-induced volatility. A shock pressure of ≤42 GPa and at a temperature of ≤1000 °C appear consistent for the formation of Lonar vesiculated melt/ feldspathic glass. Under the impact-induced shock metamorphism, maskelynite samples from the moon retain both the crystalline and amorphous domains with a distinct chemical heterogeneity attributed to different shock metamorphism effects of the plagioclase. In contrast, the martian maskelynites exhibit a smooth, homogeneous composition. The estimated shock pressure is relatively higher at ∼42–45 GPa based on experiments and models. The difference in Si/Al ratio in lunar (1–1.3) and martian maskelynite (1.5–1.9) suggests its inherent difference in composition of the crust, whereas the Lonar maskelynite shows overlapping composition with the martian maskelynite contending Lonar basalt as a potential terrestrial analogue to the martian crust. [ABSTRACT FROM AUTHOR]

Abstract The temporal duration of lunar‐evolved magmatism is still poorly constrained. In lunar meteorite Northwest Africa (NWA) 10049, a melt inclusion‐bearing zircon fragment provides a new tool to understand the composition and age of the melts from which zircon directly crystallized. The studied zircon‐hosted melt inclusions are silica rich and iron poor (e.g., ~80–90 wt% SiO2;

We conducted comprehensive Raman and Fourier transform infrared (FTIR) spectroscopic studies on the whole rock and lithic clasts of Northwest Africa (NWA) 4884 to constrain its igneous mineralogy and metamorphic characteristics. NWA 4884 is composed of mostly clinopyroxene (25.8 vol.%), pigeonite (16.6 vol.%), plagioclase (26.6 vol.%), maskelynite (8.1 vol.%), olivine (20.7 vol.%), minor tridymite (1.0 vol.%), quartz (0.2 vol.%), and ilmenite (0.5 vol.%). Lithic clasts contain mafic rocks including plutonic ultramafic cumulate, olivine gabbro, mare basalt, and feldspathic rocks including noritic anorthosite and impact melt breccia. Raman and FTIR spectroscopic analyses are combined to investigate the shock history of this breccia and revealed that NWA 4884 is highly shocked (17.9–48.1 GPa recorded in plagioclase). The combination of bulk composition and remote sensing data provides possible source regions of NWA 4884: the southern Lacus Veris (20.5°S, 84.5°W) within Orientale basin and the western mare unit (45.3°N, 151.3°E) of Campbell Crater. The pairing relationship among NWA 4884, Yamato 793274, Queen Alexandra Range 94281, and NWA 7611 is supported by their petrographic, mineral, and compositional similarities. Our work demonstrates the potential of Raman and FTIR spectroscopies to shed light on igneous petrology and the bombardment history of the Moon. [ABSTRACT FROM AUTHOR]

"Cr-Zr-Ca armalcolite" is a mineral originally found in Apollo samples five decades ago. However, no structural information has been obtained for this mineral. In this study, we report a new occurrence of "Cr-Zr-Ca armalcolite" and its associated mineral assemblage in an Mg-suite lithic clast (Clast-20) from the brecciated lunar meteorite Northwest Africa 8182. In this lithic clast, plagioclase (An = 88–91), pyroxene (Mg#[Mg/(Mg+Fe)] = 0.87–0.91) and olivine (Mg# = 0.86–0.87) are the major rock-forming minerals. Armalcolite and "Cr-Zr-Ca armalcolite" are observed with other minor phases including ilmenite, chromite, rutile, fluorapatite, merrillite, monazite, FeNi metal, and Fe-sulfide. Based on 38 oxygen atoms, the chemical formula of "Cr-Zr-Ca armalcolite" is (Ca0.99Na0.01)Σ1.00(Ti14.22Fe2.06Cr2.01 Mg1.20Zr0.54Al0.49Ca0.21Y0.05Mn0.04Ce0.03Si0.03La0.01Nd0.01Dy0.01)Σ20.91O38. Electron backscatter diffraction (EBSD) results reveal that the "Cr-Zr-Ca armalcolite" has a loveringite R 3 structure, differing from the armalcolite Bbmm structure. The estimated hexagonal cell parameters a and c of "Cr-Zr-Ca armalcolite" are 10.55 and 20.85 Å, respectively. These structural and compositional features indicate that "Cr-Zr-Ca armalcolite" is loveringite, not belonging to the armalcolite family. Comparison with "Cr-Zr-Ca armalcolite" and loveringite of other occurrences implies that loveringite might be an important carrier of rare earth elements in lunar Mg-suite rocks. The compositional features of plagioclase and mafic silicate minerals in Clast-20 differ from those in other Mg-suite lithic clasts from Apollo samples and lunar meteorites, indicating that Clast-20 represents a new example of diverse lunar Mg-suite lithic clasts. [ABSTRACT FROM AUTHOR]

The petrogenetic models of the lunar crust are built on the returned Apollo and Luna samples collected from limited parts of the lunar nearside that are chemically unusual (i.e., material rich in K, Rare Earth Elements, and P [KREEP]) and not representative of the entire lunar lithologic suite. The lunar Mg‐suite is part of this sample collection and ubiquitously has geochemical characteristics indicating the involvement of KREEP in their petrogenesis and seemed to be linked to the Procellarum KREEP Terrain (PKT). However, it is unclear if KREEP is necessary for Mg‐suite magmatism or whether Mg‐suite magmatism was a global event that occurred without significant KREEP contribution, and thus, Mg‐suite rocks outside of the PKT region may exist without containing a significant KREEP signature. Here, we investigate lunar meteorite Northwest Africa (NWA) 10401, an anorthositic troctolitic breccia with a granulitic texture. NWA 10401 shares many characteristics of Apollo Mg‐suite rocks: both its bulk rock composition and alumina content, as well as its mineralogy and mineral chemistry, are more consistent with typical Apollo Mg‐suite rocks, rather than ferroan anorthosites. In addition, olivine‐spinel equilibria calculations indicate that NWA 10401 is consistent with being derived from a common parent to the Apollo Mg‐suite troctolites. However, despite these many shared characteristics, NWA 10401 is strongly depleted in REE, starkly separating it from the typical Apollo Mg‐suite of the PKT. This indicates that NWA 10401 (and pairs) could represent a Mg‐suite component outside the PKT, and thus, KREEP‐poor Mg‐suite magmatism may have been a global phenomenon on the Moon. Plain Language Summary: Theories of the formation and evolution of the Moon's crust were built upon the returned Apollo and Luna samples that were collected from small areas of the Moon's nearside (the side that always faces Earth). These areas are now known to be chemically unusual and contain rocks that are rich in K, Rare Earth Elements (REE), and P, called KREEP. The lunar magnesian‐suite, or Mg‐suite, is part of this sample collection and represents a series of ancient rocks formed from slow cooling magmas that formed immediately after the end of magma ocean crystallization. Samples of this Mg‐suite always have chemical characteristics that indicate the involvement of KREEP in their formation, and they seemed to be linked to the Procellarum KREEP Terrain (PKT) on the Moon. However, it is unclear if (1) KREEP is needed for the formation of Mg‐suite magmatism, and thus, if Mg‐suite magmatism is limited to the geographically restricted PKT area, or (2) whether Mg‐suite magmatism was a global event that occurred without significant KREEP contribution. In this case, KREEP is simply a contamination in the Mg‐suite rocks. If (2) is true, Mg‐suite rocks outside of the PKT area on the Moon should be KREEP poor. In this study, we investigate the lunar feldspar‐rich meteorite called Northwest Africa (NWA) 10401 from the lunar highlands. Calculations indicate that NWA 10401 was produced by similar magmas that also produced the Apollo Mg‐suite troctolites. In addition, NWA 10401 shares all the characteristics of Mg‐suite rocks from the Apollo collection, except it is strongly depleted in REE. This indicates that NWA 10401 could represent a Mg‐suite rock that comes from an area other than the PKT, and thus, KREEP‐poor Mg‐suite magmatism may have been a global event on the Moon. Key Points: NWA 10401 records the highest known bulk Mg# of feldspathic lunar meteorites, with a value of 82NWA 10401 seems consistent with being derived from a common parent to the troctolites from the Apollo Mg‐suite but is KREEP poor based on major and trace element of mineral grains and bulk compositionsNWA 10401 could represent a KREEP‐poor Mg‐suite component outside the PKT indicating that Mg‐suite magmatism was not driven by KREEP and may have been a global occurrence [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 6950 is an olivine-gabbro lunar meteorite that has a distinctly different petrographic texture from other lunar basalts. In this contribution, we report the petrography, mineralogy, and U-Pb geochronology of baddeleyite and phosphate in this lunar meteorite and make a comparison with other NWA 773 paired meteorites. NWA 6950 consists mainly of coarse-grained olivine, pyroxene, and plagioclase, with minor ilmenite, chromite, troilite, baddeleyite, taenite, and apatite. The abundant rounded to euhedral olivine has a limited Fo ranging from 68 to 69. Pyroxenes include both augite and pigeonite, with a narrow range of Mg#=71–80, and composition, respectively, En46–52Fs12–16Wo32–41 and En58–68Fs19–28Wo7–20. Plagioclase is mainly anhedral, conforming to the crystal margins of olivine and pyroxene. The plagioclase grains are elongated and several hundreds of microns in length. Raman spectra shows that plagioclase has been transformed into maskelynite, which is very calcic (An87–95) with low sodium and very low potassium (Ab4–9Or0.6–3.7). The weighted mean 207Pb/206Pb ages of baddeleyite and phosphate measured using a sensitive high resolution ion micro probe (SHRIMP II) are 3119 ± 16 Ma (n = 9, MSWD = 2.5) (mean squared weighted deviates, MSWD) and 3119 ± 18 Ma (n = 15, MSWD = 2.1), respectively, giving the crystallization age of the meteorite. NWA 6950 has similar mineral compositions, geochemical characteristics, and an almost identical age of crystallization to the magnesian gabbro of the NWA 773 clan. We conclude that NWA 6950 and NWA 773 are paired meteorites, which crystallize at ca. 3119 Ma, and represent magmatic activities in the KREEP (potassium (K), rare earth elements (REE) and phosphorus (P) rich lunar material) region of the Moon. [ABSTRACT FROM AUTHOR]

The temporal duration of lunar‐evolved magmatism is still poorly constrained. In lunar meteorite Northwest Africa (NWA) 10049, a melt inclusion‐bearing zircon fragment provides a new tool to understand the composition and age of the melts from which zircon directly crystallized. The studied zircon‐hosted melt inclusions are silica rich and iron poor (e.g., ~80–90 wt% SiO2; <0.5 wt% FeO), compositionally similar with immiscible silica‐rich melts found in Apollo rocks. Nano‐SIMS U–Pb analyses of the zircon yielded a minimum crystallization age of 4,382 ± 40 Ma, older than the ages for Apollo highly evolved alkali suite lithologies (~3.8–4.33 Ga). Our study shows that the melt inclusion‐bearing zircon in NWA 10049 is the oldest microscale evidence for documenting immiscible silica‐rich melts in lunar samples, suggesting that lunar‐evolved silica‐rich melts were prevalent as early as ~4.38 Ga. This work implies that there would be a prolonged silicic magmatism occurred on the Moon. Plain Language Summary: Lunar‐evolved silica‐rich melt is thought to be related to the formation of highly silicic lithologies (e.g., granitic lithologies). These rock types have been observed in Apollo returned samples as lithic clasts and also have been detected by remote‐sensing data as silicic domes. The Apollo‐evolved lithologies give a wide range of crystallization ages from ~3.8–4.33 Ga. However, there is still unclear about the temporal duration of lunar‐evolved magmatism and volcanism. In lunar meteorite breccia NWA 10049, a melt inclusions‐bearing zircon fragment provides a new tool to understand the composition and age of the melts from which zircon directly crystallized. The studied zircon‐hosted melt inclusions are compositionally similar with immiscible silica‐rich melts found in Apollo rocks. Nano‐SIMS U–Pb analyses of the zircon yielded a minimum crystallization age of ~4.38 Ga. This age is older than the ages for Apollo‐returned granites (up to 4.33 Ga) and ancient basaltic volcanism (i.e., up to ~4.37 Ga), making the studied zircon is the oldest microscale evidence for documenting lunar silicate liquid immiscibility. Key Points: A ~200‐μm‐sized melt inclusion‐bearing zircon fragment was found in lunar feldspathic breccia meteorite NWA 10049Melt inclusions in this zircon are compositionally consistent with lunar immiscible silica‐rich meltsThe zircon is 4.38 Ga and provides microscale evidence for ancient immiscible silica‐rich melt on the Moon [ABSTRACT FROM AUTHOR]

Determining the formation mechanism of maskelynite is essential to understanding the shocked environments of meteorites on their parent bodies. Maskelynite has been accepted as a diaplectic glass for several decades, but there have been suggestions that it is a normal glass quenched from a dense melt. Morphological characteristics have been generally investigated to identify the formation mechanism of amorphous plagioclase in meteorites, but the chemical difference between crystalline and amorphous plagioclase has not been fully understood. In this study, we investigated the morphological, atomic‐scale structural, and chemical characteristics of amorphous plagioclase in the lunar meteorite DEW 12007 to constrain its formation mechanism via chemical analysis. The morphological characteristics showed that plagioclase was partially converted into amorphous phase through partial melting. Two‐dimensional Raman mapping confirmed the structural difference between amorphous and crystalline regions. Quantitative chemical analyses revealed that the amorphous regions were more albite‐rich than the crystalline regions, likely due to the partial melting of plagioclase. Under shocked conditions, the partial melting of plagioclase induced a chemical variation between amorphous and crystalline regions. The morphological and structural changes correspond well with the chemical variations, indicating that amorphization induced such variations. The chemical differences between amorphous and crystalline plagioclase in other meteorites also could be understood to be the results of partial melting. Thus, the chemical differences between amorphous and crystalline plagioclase in partially amorphized grains could elucidate the formation mechanism of amorphous plagioclase in many meteorites. Plain Language Summary: Amorphous plagioclase is a type of mineral used as a shock indicator in meteorites. It can be formed by solid state transformation or melting depending on the shock environment. We studied the morphology and chemical characteristics of plagioclase grains from the lunar meteorite DEW 12007, found in Antarctica. A portion of each plagioclase grain was changed into an amorphous phase during the shock event while the rest was left as a crystalline phase. The morphology of the plagioclase grain indicates that the partial amorphization occurred by partial melting, not by solid state transformation. Partial melting also caused a chemical difference between the amorphous and crystalline parts of the plagioclase grain. Previous works showed that the solid state transformation does not generate a chemical difference between amorphous and crystalline parts of plagioclase grains. Thus, the formation mechanism of amorphous plagioclase can be determined by comparing the chemical composition of amorphous and crystalline plagioclase in meteorites. Key Points: A chemical difference between crystalline and amorphous phase was observed in partially amorphized plagioclase from meteorite DEW 12007Partial melting could induce the more albite (or anorthite)‐rich amorphous plagioclase in partially amorphized plagioclase grainThe formation mechanism of amorphous plagioclase in meteorites can be revealed by both morphological and chemical analyses [ABSTRACT FROM AUTHOR]

The Northwest Africa (NWA) 773 clan of meteorites is a group of paired and/or petrogenetically related stones that contain at least six different lithologies: magnesian gabbro, ferroan gabbro, anorthositic gabbro, olivine phyric basalt, regolith breccia, and polymict breccia. Uranium-lead dates of baddeleyite in the magnesian gabbro, ferroan gabbro, and components within breccia lithologies of paired lunar meteorites NWA 773, NWA 3170, NWA 6950, and NWA 7007 indicate a chronologic link among the meteorites and their components. A total of 50 baddeleyite grains were analyzed and yielded weighted average 207 Pb- 206 Pb dates of 3119.4 ± 9.4 ( n = 27), 3108 ± 20 ( n = 13), and 3113 ± 15 ( n = 10) Ma for the magnesian gabbro, ferroan gabbro, and polymict breccia lithologies, respectively. A weighted average date of 3115.6 ± 6.8 Ma ( n = 47/50) was calculated from the baddeleyite dates for all lithologies. A single large zircon grain found in a lithic clast in the polymict breccia of NWA 773 yielded a U-Pb concordia date of 3953 ± 18 Ma, indicating a much more ancient source for some of the components within the breccia. A U-Pb concordia date of apatite and merrillite grains from the magnesian gabbro and polymict breccia lithologies in NWA 773 is 3112 ± 33 Ma, identical to the baddeleyite dates. Magnesian and ferroan gabbros, as well as the dated baddeleyite and Ca-phosphate-bearing detritus in the breccia lithologies, formed during the same igneous event at about 3115 Ma. These data also strengthen proposed petrogenetic connections between magnesian and ferroan gabbro lithologies, which represent some of the youngest igneous rocks known from the Moon. [ABSTRACT FROM AUTHOR]

As the most KREEP-rich lunar sample, the Sayh al Uhaymir (SaU) 169 meteorite would provide more valuable information concerning the KREEP and early lunar evolution of the Moon if its source regions can be pinpointed. Previous studies proposed Lalande crater as the source region that corresponds to the impact event of ~2.8 Ga recorded in SaU 169, whereas this linkage is highly dependent on the age determination of the potential source crater. By counting craters superposed on the ejecta blankets of Lalande and modelling the burial process of these superposed craters by Lalande's ejecta, we find that the crater statistics around Lalande are heavily influenced by the existing of pre-Lalande craters larger than ~170 m in diameter, which could lead to a largely overestimated age of Lalande crater. After taking this influence into consideration, we obtain that Lalande crater is a Copernican crater with a formation age of 410 ± 20 Ma, and the adjacent mare basalts unit has an Imbrian age of 3.8 −0.06 +0.04 Ga. The formation age of Lalande crater is inconsistent with any of the radio-isotopic ages recorded in SaU 169, indicating that Lalande crater is unlikely to be the source region of this lunar meteorite. • Lalande crater is a Copernican crater with a formation age of 410 ± 20 Ma. • The adjacent mare basalts unit has an Imbrian age of 3.8 −0.06 +0.04 Ga. • Lalande crater is not likely the source region of the KREEP-rich meteorite Sayh al Uhaymir 169. • The pre-existing craters heavily influence the age determination of Lalande crater. [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 2977 is a lunar basaltic meteorite that was found in 2005 and has been classified as an olivine cumulate gabbro. This meteorite contains a shock melt vein (SMV) induced by an intense shock event. We report herein on an in-situ analysis of phosphates in the host gabbro and the shock vein for the U-Pb dating of NWA 2977 using an ion microprobe, NanoSIMS. The majority of the analyzed phosphates, in both the SMV and host-rock, lie on a linear regression in 238 U/ 206 Pb- 207 Pb/ 206 Pb- 204 Pb/ 206 Pb three-dimensional space, indicating a total Pb/U isochron age of 3.15±0.12 Ga (95% confidence level), which is consistent ages determined in previous isotopic studies of NWA 2977 (Sm-Nd age of 3.10±0.05 Ga, Rb-Sr age of 3.29±0.11 Ga, and Pb-Pb baddeleyite age of 3.12±0.01 Ga), and identical to the age of the U-Pb phosphate in a paired meteorite NWA 773, 3.09±0.20 Ga, derived from our dataset. There was no clear difference in the formation age between the phosphates found in the SMV and host-rock, although the shape and size of the grains and the Raman spectra show the evidence of intense shock metamorphism. Based on these findings, the cooling rate of the phosphate was very rapid, constrained to be larger than 140 K/s., (Copyright © 2023 Narumi Moromoto, Yosuke Kawai, Kentaro Terada, Masaaki Miyahara, Naoto Takahata, Yuji Sano, Naoko Fujikawa, and Mahesh Anand.)

Noble gases and nitrogen have been in lunar meteorite from antartcica: the polymict regolith breccias, Yamato-983885 (hereafter Y-983885). Y-983885 has highest concentration of trapped noble gases (Ar, Kr, and Xe) among all the lunar meteorites and returned lunar samples. Noble gases and nitrogen abundances measured in two samples of the lunar meteorite Y-983885. The concentration of trapped noble gases in Y-983885 (A) are, 20 Ne=3.69×10 −3 , 36 Ar=12.6×10 −4 , 84 kr=8.57×10 −7 and 132 Xe=1.63×10 −7 ccSTP/g. The cosmic-ray exposure ages for Y-983885 are thus calculated to be T 21 (A)=1592±232 Ma and T 21 (B)=574±85 Ma for 2π geometry (using production rates as per Hohenberg et al., 1978 and bulk composition ). The exposure ages of samples A and B differ, indicating that they have undergone different exposure scenarios on the lunar surface. The different irradiation ages ( T 21 (A)=1592±232 Ma and T 21 (B)=574±85 Ma) indicates that the regolith material which constitutes the meteorite Y-983885 resided at different shielding depths on lunar surface before agglomeration into the final meteorite. Exposure ages calculated using end member compositon like norite, basalt, tractolite (1947 to 1365 and 711 to 455 for A and B respectively) indicates clearly that the two samples A and B has undergone different exposure on Moon. The 20 Ne/ 22 Ne ratio of 13.60±0.01 in temperature step 400 °C of Y-983885 (A) demonstrate a clear retention of solar wind signature in this meteorite. The presence of high contents of trapped solar wind gases indicates that Y-983885 consists of mature lunar regolith material. Variable amounts of solar gases as well as cosmogenic noble gases indicate that Y-983885 (A and B) is compacted from several fragments that were exposed at the surface and/or at various depths in the regolith, before becoming part of Y-983885. [ABSTRACT FROM AUTHOR]

Among the lunar samples that were returned by the Apollo missions are many cumulate plutonic rocks with high Mg# [molar Mg/(Mg+Fe) in %] and abundances of KREEP elements (potassium, rare earth elements, phosphorus, U, Th, etc.) that imply KREEP-rich parental magmas. These rocks, collectively called the magnesian suite, are nearly absent from sampling sites distant from Imbrium basin ejecta, including those of lunar highlands meteorites. This absence has significant implications for the early differentiation of the Moon and its distribution of heat-producing elements (K, Th, U). Here, we analyze a unique fragment of basalt with the mineralogy and mineral chemistry of a magnesian suite rock, in the lunar highlands meteorite Allan Hills (ALH) A81005. In thin section, the fragment is 700 x 300 urn, and has a sub-ophitic texture with olivine phenocrysts, euhedral plagioclase grains (An97-70),and interstitial pyroxenes. Its minerals are chemically equilibrated. Olivine has Fe/Mn ~ 70 (consistent with a lunar origin), and Mg# ~80, which is consistent with rocks of the magnesian suite and far higher than in mare basalts. It has a rich suite of minor minerals: fluorapatite, ilmenite, Zr-armalcolite, chromite, troilite, silica, and Fe metal (Ni = 3.8%, Co = 0.17%). The metal is comparable to that in chondrite meteorites, which suggests that the fragment is from an impact melt. The fragment itself is not a piece of magnesian suite rock (which are plutonic), but its mineralogy and mineral chemistry suggest that its protolith (which was melted by impact) was related to the magnesian suite. However, the fragment's mineral chemistry and minor minerals are not identical to those of known magnesian suite rocks, suggesting that the suite may be more varied than apparent in the Apollo samples. Although ALHA81005 is from the lunar highlands (and likely from the farside), Clast U need not have formed in the highlands. It could have formed in an impact melt pool on the nearside and been transported by meteoroid impact. Lunar highlands meteorites should be searched for rock fragments related to the magnesian-suite rocks, but the fragments are rare and may have mineral compositions similar to some meteoritic (impactor) materials. [ABSTRACT FROM AUTHOR]

This study explores the petrogenesis of Shişr 161, an immature lunar regolith breccia meteorite with low abundances of incompatible elements, a feldspathic affinity, and a significant magnesian component. Our approach was to identify all clasts >0.5 mm in size in a thin section, characterize their mineral and melt components, and reconstruct their bulk major and minor element compositions. Trace element concentrations in representative clasts of different textural and compositional types indicate that the clast inventory of Shişr 161 is dominated by impact melts that include slowly cooled cumulate melt rocks with mafic magnesian mineral assemblages. Minor exotic components are incompatible-element-rich melt spherules and glass fragments, and a gas-associated spheroidal precipitate. Our hypothesis for the petrologic setting of Shişr 161 is that the crystallized melt clasts originate from the upper ~1 km of the melt sheet of a 300 to 500 km diameter lunar impact basin in the Moon's feldspathic highlands. This hypothesis is based on size requirements for cumulate impact melts and the incorporation of magnesian components that we interpret to be mantle-derived. The glassy melts likely formed during the excavation of the melt sheet assemblage, by an impact that produced a >15 km diameter crater. The assembly of Shişr 161 occurred in a proximal ejecta deposit of this excavation event. A later impact into this ejecta deposit then launched Shişr 161 from the Moon. Our geochemical modeling of remote sensing data combined with the petrographic and chemical characterization of Shişr 161 reveals a preferred provenance on the Moon's surface that is close to pre-Nectarian Riemann-Fabry basin. [ABSTRACT FROM AUTHOR]

Oscillatory zoning in silicate minerals, especially plagioclase, is a common feature found in volcanic rocks from various terrestrial tectonic settings, but is nearly absent in the lunar environment. Here we report backscattered electron images, quantitative wavelength-dispersive spectrometry (WDS) analyses, and qualitative WDS elemental X-ray maps that reveal oscillatory zoning of Mg, Ca, Fe, Ti, Al, Cr, and Mn in euhedral pyroxene phenocrysts, and faint oscillatory zoning of P in olivine phenocrysts in basaltic lunar meteorite Northwest Africa (NWA) 032. This is only the third known occurrence of oscillatory zoning in lunar silicate minerals. Zoning bands in pyroxene range from ~3-5 µm up to ~60 µm in width, but are typically ~10-20 µm in width. Oscillatory bands are variable in width over short distances, often within a single grain. Most oscillatory bands preserve a euhedral form and have sharp edges; however some bands have jagged or uneven edges indicative of resorption surfaces. The short-scale oscillatory nature of the zoning in pyroxene is overprinted on longer-scale core to rim normal magmatic zoning from pigeonite to augite compositions. Oscillatory zoning of P in olivine is faint and only resolvable with high beam current (400 nA) mapping. Bands of higher P are typically only a few micrometers in width, and although they preserve a euhedral form, they are not traceable around the full circumference of a grain and have variable spacing. Resorption surfaces, longer-scale normal magmatic zoning, and relatively thick oscillatory bands are indicative of the formation of these chemical oscillations as a result of variable magma composition. Pyroxenes likely experienced variable liquid compositions as a result of convection in a differentially cooling, chemically stratified magma chamber. Periodic replenishments of progressively decreasing volumes of primitive parental magma are also permissible and may have enabled convection. In a convection model, Mg-rich bands reflect growth in the lower, warmer, more crystal-poor regions of the chamber, whereas Ca-Al-Ti-Cr-rich bands reflect growth in the upper, cooler, more crystal-rich regions of the chamber. The limited duration of crystallization in the magma chamber and the slow diffusion rates of multiple elements among multiple crystallographic sites in clinopyroxene, combined with fast cooling upon eruption, act to preserve the oscillatory zoning. Oscillatory zoning of P in olivine is a product of solute trapping resulting from the slow diffusion of P in silicate melts and minerals, and relatively fast magma cooling rates that may be related to magma chamber convection. Differential cooling of the chamber and the fast cooling rates within the chamber are likely a product of the thermal state of the lunar crust at 2.93 Ga when NWA 032, which is currently the youngest dated lunar igneous rock, erupted onto the surface of the Moon. [ABSTRACT FROM AUTHOR]