Impactites Research Articles

Extremely large Cl isotopic fractionation in Chang'e-5 impact glass beads

Lunar materials have recorded a very large δ37Cl variation, and the mechanism causing this variation has yet to be determined. We measured the F and Cl contents and the δ37Cl in Chang'e-5 impact glass beads using a nanoscale secondary ion mass spectrometry. These glass beads exhibit the largest δ37Cl variation observed to date, ranging from –0.7 ‰ to 119 ‰. Furthermore, the δ37Cl values are roughly negatively correlated with the Cl concentration. The correlations between F and Cl concentrations differ for homogeneous and heterogeneous glass beads. Our calculations indicate that NaCl (g) and HCl (g) degassing may have been the pivotal mechanism that elevated the δ37Cl value, with >50 % of Cl in the melt evaporating during glass formation. The glass beads may have incorporated the chlorine species condensed from early evaporation. Our results provide direct evidence to constrain the impact-induced degassing process of Cl on airless celestial bodies.

Geochemical evidence for a chondritic impactor in altered impact glass from the Stac Fada Member impactite, NW Scotland

The Stac Fada Member (Stoer Group) is a ∼1.2 Ga melt-rich impact breccia whose source crater and, therefore, proximity remains debated. We present a detailed in situ geochemical dataset for altered impact melt clasts within Stac Fada samples from Bay of Stoer and Second Coast. These altered impact melt clasts are now predominantly composed of clinochlore. Geothermometry of this clinochlore indicates formation temperatures within the ejecta blanket at 188–231°C, in agreement with previous estimates. A positive correlation between platinum group elements Ir, Pt and Rh – apparently independent of Ni – indicates two geochemical sources for platinum group elements enrichment. We propose that these represent an Mg–Ni-rich chondritic impactor and a mafic/ultramafic-layered body within the target lithology. Spatial variation in Ni content suggests that geochemical data, in combination with field observations, may be instrumental in assessing the likely location of the impact crater.

Polydopamine-primed FeCo-LDH endowed epoxy resin with enhanced flame retardancy and mechanical properties

The integration of layered double metal hydroxides (LDH) into epoxy resin (EP) for flame retardancy is in line with the principles of environmentally friendly and sustainable development. In this study, polydopamine (PDA)-primed intercalated LDH containing iron and cobalt ions (LDH-DBS@PDA) was prepared, and its chemical composition, structure and morphology were thoroughly characterized. Due to the synergistic flame-retardant properties exhibited by LDH and PDA, as well as the catalytic charring properties of iron and cobalt ions in both condensed and gaseous phases, EP composite with 5 wt% LDH-DBS@PDA achieved a UL-94 V-0 rating with a limiting oxygen index of 30.7 %. Moreover, EP/LDH-DBS@PDA exhibited a significant decrease in total heat release by 48 % and smoke release by 52 %, demonstrating remarkable fire safety performance. Additionally, the existence of LDH-DBS@PDA improved impact strength, tensile strength, and glass transition temperature due to strong interactions between PDA and EP matrix. This work presents a promising strategy for developing highly efficiency flame retardants with excellent compatibility for polymeric materials.

Impact-dispersed Fe–Fe1−xS core–shell particles in Chang’e-5 lunar soil impact glass

Lunar soil undergoes space weathering and accumulates optically active opaque particles (OAOpq) of different sizes, resulting in a darkening or red shift of the reflectance spectrum. The surfaces of weakly weathered objects exhibit spectral characteristics of strong weathering; these mechanisms are still unclear. The causes of OAOpq in lunar soil are complex, especially for submicrometer particles, which account for the largest mass proportion. We found ubiquitous impact-dispersed Fe–Fe1-xS core–shell particles in Chang’e-5 lunar soil impact glass and splatter. The crystal structure, particle size distribution, and chemical composition of OAOpq in the impact glass indicate that these OAOpq consist of sulfides or metals from multiple sources. Thermodynamic evidence, diffusion behavior, and particle dispersion characteristics indicate that impact dispersion is the most likely formation mechanism of these OAOpq. The proposed impact dispersion provides a reason for the large number of OAOpq and the limited products for in situ reactions. This process explains why lunar soil with a low degree of weathering exhibits substantial spectral modification properties. The results provide insights into space weathering of the lunar surface and also imply that impact-dispersed OAOpq may be the primary modification type on asteroid surfaces. The unique chemical properties of Fe–Fe1-xS OAOpq also indicate that the lunar regolith has the potential for resource utilization.

Multiple sources of water preserved in impact glasses from Chang'e-5 lunar soil.

The existence of molecular H2O and evolution of solar wind-derived water on the lunar surface remain controversial. We report that large amounts of OH and molecular H2O related to solar wind and other multiple sources are preserved in impact glasses from Chang'e-5 (CE5) lunar soil based on reflectance infrared spectroscopy and nanoscale secondary ion mass spectrometry analyses. The estimated water content contributed by impact glasses to CE5 lunar soil was ~72 ppm, including molecular H2O of up to 15 to 25 ppm. Our studies revealed that impact glasses are the main carrier of molecular H2O in lunar soils. Moreover, water in CE5 impact glasses provides a record of complex formation processes and multiple water sources, including water derived from solar wind, deposited by water-bearing meteorites/micrometeorites, and inherited from lunar indigenous water. Our study provides a better understanding of the evolution of surficial water on airless bodies and identifies potential source and storage pathways for water in the terrestrial planets.

A two stage impact melting process in an impact glass strewn field from the Atacama Desert

A two stage impact melting process in an impact glass strewn field from the Atacama Desert

Zircon microstructures record high temperature and pressure conditions during impact melt evolution at the West Clearwater Lake impact structure, Canada

Evolution of impact melt in terms of initial melt temperatures, melt transport, and cooling history, is a process that remains to be fully understood. Theoretical predictions had suggested that impact melts can experience temperatures far exceeding those in endogenous igneous settings. Direct evidence of the hottest temperatures recorded in impactites was observed recently at the Mistastin Lake impact structure, Canada. The former presence of cubic zirconia, a polymorph of ZrO2 that forms at >2370 °C, was documented within impact glass. In this work, we investigated the zircon and zirconia microstructures and crystallographic orientation relationships with electron backscatter diffraction in two impact glass samples from West Clearwater Lake impact structure in Quebec, Canada. Here we present the first report of the former presence of cubic zirconia, indicating a superheated melt temperature of >2370 °C in one of two impact glass samples analysed. Our results make West Clearwater Lake impact structure the second terrestrial structure with confirmed evidence of former cubic zirconia. Furthermore, we found evidence of melt superheating to temperature of 1673 °C in the other impact glass sample. We also document the first occurrence of former reidite in granular neoblastic (FRIGN) zircon grains in the two impact glass samples analysed in this work, giving us a minimum shock pressure estimate of 20 GPa. This study highlights the heterogeneous thermodynamic (high temperature/low pressure, high pressure, and low temperature/ low pressure) conditions recorded within impact glass from West Clearwater Lake impact structure.

Helium reservoirs in iron nanoparticles on the lunar surface

The Moon’s surface is directly exposed to the space environment and subject to alteration by space weathering. One agent of space weathering, the solar wind, enriches the lunar surface with helium. Although we understand how helium is delivered to the Moon, certain aspects of helium concentration processes on the surface remain unknown, such as why impact-generated glass aggregates contain more helium than equally sized soil grains of other types. Here we have analyzed the contents of vesicular iron nanoparticles in lunar impact glasses using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy and show that the nanoparticles contain high concentrations of helium (10-24 atoms/nm3). The widespread occurrence of vesicular iron nanoparticles among lunar samples suggests that they may be an important helium reservoir. These results also suggest that space weathering of iron-rich minerals plays a role in helium sequestration on the Moon and potentially on other airless bodies.

Iron‐Rich Grain‐Decorated Depressions on Surfaces of Lunar Impact Glasses

AbstractIron‐rich particles are widespread on the surfaces and interiors of lunar impact glasses, and they record delicate physicochemical processes during space weathering and regolith gardening on the Moon. Different from nanophase iron in amorphous rims of regolith minerals, iron‐rich particles in lunar impact glasses are mostly larger than 10 nm and are spherical and semi‐hemispherical in shape. In regolith samples returned by Luna, Apollo and Chang'E‐5 missions, a special form of microscopic iron‐rich structure commonly exists on surfaces of impact glasses, which appear as rimless depressions that are filled with nano‐sized grains. Termed grain‐decorated iron‐rich depressions, their possible origin is elusive. Here we perform detailed observations of the morphology, composition and crystallography of these microstructures, showing that they are not degassing pits that were later filled with nano‐sized grains as has been previously considered. They are hemispherical integrated compounds of α‐Fe and troilite that have variable area proportion. The surface grains are dominated by α‐Fe, which mainly develop on top of vesiculated surfaces of the underlying troilite. The α‐Fe grains are mainly formed by desulphurization of troilite due to radiation and heating. While iron‐rich grain‐decorated depressions have larger diameters and different surface morphologies compared to other iron‐rich microstructures in lunar impact glasses, their identical occurrences and phase components (α‐Fe and troilite) suggest a common origin caused by liquid immiscibility between Fe‐S melt and silicate melt. Their diverse surface morphology is mainly caused by heterogeneous S contents and local ratios of Fe and S in silicate impact melt.

Redox condition changes caused by impacts: Insights from Chang’e-5 lunar glass beads

Lunar materials are overall more reducing compared with their terrestrial counterparts, but the mechanism remains to be elucidated. In this study, we present a possible explanation for the changes in redox state of the lunar regolith caused by impact events, based on our investigations of the impact glass beads from Chang’e-5 mission. These glass beads contain iron metal grains and show concentration gradients of FeO and K2O (with or without Na2O) from their rims to centers. The compositional profiles exhibit error-function-like shapes, which indicates a diffusion-limited mechanism. Our numerical modeling results suggest that the iron metal grains on the surface of the glass beads were generated through the reduction of FeO by elemental K and (or) Na produced during the impact events. Meanwhile, the iron metal grains inside the bead may have formed due to oxygen diffusion driven by redox potential gradients. Furthermore, our study suggests that impact processes intensify the local reducing conditions, as evidenced by the presence of calcium sulfide particles within troilite grains that coexist with iron metal grains on the surface of the glass beads. This study provides insights into the oxygen diffusion kinetics during the formation of iron metal spherules and sheds light on the changes in redox conditions of lunar materials caused by impact events.

Iron projectile fractionation processes in siliceous glass from small impact craters

Detection of extra-terrestrial geochemical components in melt generated during meteorite impact provides diagnostic evidence that can be used to confirm a hypervelocity impact event, and in some cases, classify the projectile. However, projectile contamination is often present at sub-percent levels, and can be difficult to detect. In contrast, meteoritic abundances in glass from small impact craters (<1 km diameter) formed by iron meteorites can be anomalously high, which has been attributed to glass originating from the projectile-target interface. Emulsion textures, immiscible liquids, metal spherules, and non-meteoritic siderophile element ratios have been cited as evidence that the projectile component is typically fractionated in impact glass. Here we present compositional data for impact glass from the Henbury crater field in Australia, where the largest crater is 145 m in diameter and the subgreywacke target rock and IIIAB iron projectile are geochemically distinct. Mixing models (Fe-Si, Ni-Co, Cr-Ir) and high platinum group element abundances indicate average projectile contributions ranging from 3 to 13 % in Henbury glass, comparable to ranges reported in glass from the Kamil (Egypt) and Wabar (Saudi Arabia) impact craters. However meteoritic siderophile element ratios (Fe:Ni, Fe:Co, Ni:Co) in Henbury glass appear nearly unfractionated, whereas Wabar and Kamil glasses have more fractionated ratios. Observed variations are attributed to fractionation of meteoritic Ni by formation of immiscible Ni-rich spherules during oxidation of meteoritic iron, and subsequent separation of Ni-rich spherules from glass during ejection. The Henbury glass sample analyzed is interpreted as an example of an interface melt that quenched prior to extensive oxidation and phase separation, and thus may represent one of the least fractionated samples of melt from the projectile-target interface described thus far, whereas Wabar and Kamil glasses record more evidence of fractionation processes. These results further highlight the influence of metal spherule formation on the composition of ejected glass from small impact structures formed by iron meteorites and provide new insights that explain textural features observed in natural impact glasses.

Aouelloul impact crater, Mauritania: New structural, lithological, and petrographic data

The Aouelloul circular structure (Mauritania), 0.4 km in diameter, is a simple impact crater, which formed approximately 3 Myr ago. The Aouelloul crater was confirmed to be an impact crater based on the presence of an extraterrestrial component in glass fragments found around the crater, but so far, no convincing evidence of shock metamorphism in minerals, such as shocked quartz grains, is reported. The crater has been visited by a small number of geologists and limited information is available on deformations and impact-related effects at the macroscopic and microscopic scales. Detailed petrographic investigations of eight sandstone samples, all collected at the rim of Aouelloul during a 2019's field campaign, show that tectonic deformation lamellae occur in a number of quartz grains, but did not reveal any evidence of shock metamorphism. New observations on the distribution of the impact glass at the Aouelloul crater, exclusively located in the southern and eastern outer parts of the crater, suggest an oblique impact, from possible directions ranging from south-west to north (clockwise). Geological and lithostructural data are also presented and show that the rim of the crater is characterized by more or less disturbed metric to pluri-metric blocks of rocks showing fracturing and dipping toward either the interior or the exterior of the crater. This study confirms previous works conducted at the Aouelloul crater and illustrates the difficulty in demonstrating the impact origin of relatively small craters.

Lunar Evolution in Light of the Chang'e-5 Returned Samples

The Chinese spacecraft Chang'e-5 (CE-5) landed on the northern Ocean Procellarum and returned 1,731 grams of regolith. The CE-5 regolith is composed mostly of fragments of basalt, impact glass, agglutinates, and mineral fragments. The basalts could be classified as of a low-Ti and highly fractionated type based on their TiO2 content of ∼5.3 wt% and Mg# of ∼28. Independent of petrographic texture, the CE-5 basalts have a uniform eruption age of 2,030 ± 4 Ma, demonstrating that the Moon remained volcanically active until at least ∼2.0 Ga. Although the CE-5 landing site lies within the so-called Procellarum KREEP [potassium (K), rare earth elements (REE), and phosphorus (P)] Terrane, neither the CE-5 basalts nor the mantle source regions of those basalts were enriched in KREEP components, such as incompatible elements, water, sulfur, or chlorine. Therefore, it would be a new and stimulating task in the future to look for the triggering mechanism of the young volcanism on the Moon. ▪The CE-5 spacecraft returned 1,731 grams of lunar regolith in December 2020. It was the first new lunar sample since the last collection in August 1976.▪CE-5 regolith is basaltic in chemical composition, with only ∼1% highland materials of anorthosite, Mg suite, alkali suite, and KREEP.▪The CE-5 basalt is low Ti and highly differentiated. It was extruded at ∼2.0 Ga, being the youngest lunar basalt identified so far from the Moon.▪The triggering mechanism of the ∼2.0 Ga lunar volcanism is not clearly understood because its mantle source was dry and contained low abundances of KREEP elements.

Deterioration of 3D printed multicomponent radiotherapy dosimetry phantom’s properties upon high energy irradiation

Accuracy and realization of the prescribed dose in radiotherapy is one of the crucial ways to ensure the quality of the treatment, which usually is closely related to the use of different types of phantoms. Nowadays 3D printing technology is a promising methodology for the fabrication of phantoms, mimicking different biological tissues. Therefore, analysis of the structural properties of materials and their deterioration due to the irradiation is an important issue. This study is aimed to assess radiation-induced changes of the physical and mechanical properties of 3D printed materials used in the construction of the advanced multicomponent dosimetry phantom for radiotherapy when high energy (6 MeV) X-ray photons were applied for irradiation. Irradiation dose of 70 Gy, representing total dose delivered to the target during the whole treatment procedure prescribed for a patient was applied. Composites filaments with TiO2 additive were extruded using a 3D Devo filament extruder and experimental samples were printed using 3D printer Zortrax M300. Attenuation properties of the samples were simulated using the XCOM database, while mechanical tests were performed using the ElectroPuls® E10000 Linear-Torsion machine. It was observed that 6 MeV photons irradiation of the investigated composites (polyethylene terephthalate glycol (PETG), Polylactic acid (PLA), High Impact Polystyrene (HIPS), ULTRAT ABS and GLASS) and PLA containing various concentrations of TiO2 additives (0 %, 0.5 %, 1.0 % and 2.0 %)) has not induce d significant deterioration of samples’ attenuation and mechanical properties, indicating variations within interval of 5 % − 10 %. However, performed investigation also revealed some improvement of structural and mechanical properties of 3D printed PLA composites with incorporated TiO2.

Submicroscopic iron-rich grains throughout impact glasses in Chang'E-5 regolith

In lunar regolith returned by Chang'E-5, Apollo and Luna missions, submicron-sized iron-rich grains that are dominated by reduced iron and with sizes of about 10 s to 100 s nanometers are widespread on surfaces of impact glasses, such as glass spherules and glass that welds agglutinates. With flat or mound-like tops, such submicroscopic iron-rich grains typically occur in chains, nets and/or mists, and they were interpreted to be surface adherents that are mainly composed of native iron. Processes such as cooling of iron melt veneer, condensation of iron vapor, and in situ thermal reduction of regolith particles have been separately invoked to explain their origin. Meanwhile, some iron-rich grains have lower hemispheres being embedded in their host glasses, and spherical iron-rich grains with similar sizes, compositions and spatial distributions are also widespread in interiors of their host glasses. It is possible that both the surface and interior iron-rich grains were formed simultaneously during cooling of the host impact melt. However, the precise composition and crystallography of the surface and interior iron-rich grains have not been adequately constrained. In this study, we prepared focused ion beam (FIB) sections for chains of iron-rich mounds that occur on surfaces of impact glasses in the Chang'E-5 lunar regolith. Several FIB sections also exposed interior iron-rich grains that exhibit similar sizes and regular distribution patterns. High-resolution elemental mapping shows that both the surface and interior iron-rich grains are mainly composed of iron and sulfur, and crystallographic inspections reveal that the grains are similarly composed of α-Fe and troilite with varying volume proportions. As the glass spherules and agglutinate glasses are mainly melt products of local regolith materials, both the surface and interior iron-rich grains are most consistent with being formed due to liquid immiscibility between FeS and silicate melt. Troilite preferentially occurs along margins of the iron-rich grains due to heterogeneous distribution of S in the iron-rich melt and the relatively greater compatibility between troilite and silicate melt. The varying morphology of the surface iron-rich grains (e.g., flat tops, mounds) is likely caused by different surface tensions of FeS melt droplets and different wettability between the solidifying Fe-dominating melt and FeS melt with silicate melt. This interpretation predicts that iron-rich grains formed during cooling of impact melt may be dispersed in melt strips and even detached from the melt body during ejecta motion, and they could be subsequently adhered to surfaces of other lunar regolith particles. For reflectance spectra of lunar regolith at visible to near-infrared wavelength, the long-noticed darkening effect caused by submicron-sized iron may be caused by such two-phase iron-rich grains (i.e., α-Fe plus troilite).

Геохимия органического вещества природных битумов в разрезе р. Кожвы (Тимано-Печорская провинция)

The objects of study are diaplectic and melt silicate glasses from vein melt impactites of the Kara astrobleme. Microscopic and spectroscopic characteristics of two glasses with fundamentally different formation mechanisms were obtained, which allowed comparing their structural features. We found that silicate diaplectic and melt impact glasses from high-pressure/high-temperature vein bodies of the Kara astrobleme were characterized by similar structural features — a high degree of polymerization, the presence of four-membered and polymembered SiO4 rings, which was characteristic of all glasses were the SiO2 composition. Diaplectic glasses are characterized by the constant presence of three-membered SiO4 rings; melt glasses were characterized by the absence of this feature, which was determined by more extreme conditions for the glass from melt.

Сравнительная характеристика диаплектовых и расплавных силикатных стёкол Карской астроблемы

The objects of study are diaplectic and melt silicate glasses from vein melt impactites of the Kara astrobleme. Microscopic and spectroscopic characteristics of two glasses with fundamentally different formation mechanisms were obtained, which allowed comparing their structural features. We found that silicate diaplectic and melt impact glasses from high-pressure/high-temperature vein bodies of the Kara astrobleme were characterized by similar structural features — a high degree of polymerization, the presence of four-membered and polymembered SiO4 rings, which was characteristic of all glasses were the SiO2 composition. Diaplectic glasses are characterized by the constant presence of three-membered SiO4 rings; melt glasses were characterized by the absence of this feature, which was determined by more extreme conditions for the glass from melt.

Petrogenesis of magnesian troctolitic granulite clasts from Chang'e -5 drilling sample: Implications for the origin of ejecta material from lunar highlands

The lunar soil collected by the Chang'e-5 (CE-5) mission contains both local materials and components of various sources. The latter could have derived from the excavation of impact craters in the highlands away from the landing site, providing valuable information on the composition of the lunar crust beyond the mare basalts sampled by the CE-5 mission. In this study, we examined the mineralogy and petrology of magnesian troctolitic granulites (or troctolites) recovered in the CE-5 soil. The troctolites exhibit a granoblastic texture but have a finer grain size compared to Apollo granulites, and almost all plagioclase remains unaltered and not converted to maskelynite. The major element composition shows a SiO2 content of 45.4 wt%, CaO of 12 wt%, TiO2 of 0.2 wt%, Th of 0.1 ppm, and an Mg# of 76, lower than those of the Mg troctolitic lunar meteorites NWA 5744 and NWA 10401. The trace element budget indicates that the magnesian troctolites are KREEP-poor, which distinguishes them from the Mg-suite rocks in Apollo samples but is similar to some troctolitic lunar meteorites (NWA 10401). Furthermore, we predict –by using MELTS modeling– a plausible genetic connection between the Mg-suite rocks, and our troctolites, suggesting that the latter may be pristine and formed during a later stage along a fractional crystallization path. This scenario challenges the hybridization model and strengthens the evidence in favour of the fractional crystallization modeling. To ascertain the potential origin crater for the magnesian granulites, a comparative analysis was conducted with NWA 10401. Based on our findings, we propose that the Pythagoras crater, situated north of the CE-5 landing site, is the most probable source of the aforementioned magnesian troctolitic granulites. The ejecta from this crater may have been deposited between the Eratosthenian-aged mare basalts and the Imbrian-aged mare basalts beneath the CE-5 landing site. The KREEP-poor troctolitic granulite in the Chang'e-5 soil could represent paleo-ejecta from Pythagoras crater, excavated by subsequent impacts on the Eratosthenian-aged basalts and delivered them to the CE-5 site. The original location of the Mg troctolitic granulites is inferred to be near-surface, buried by the uppermost crustal rocks (<10 km), which is consistent with its contact with feldspathic impact glass.

Complex characteristics of suevites at the B. Vanuyta river (Kara astrobleme, Russia)

Research subject. Suevites from the eastern sector of the Kara astrobleme, located in the basin of the Bolshaya Vanuyta river. Aim. To identify the suevitic type and to clarify the facial features of the suevites from the B. Vanuyta River. Materials. Hand-size samples of suevites collecteed in the basins of B. Vanuyta, Anaroga, Kara, and Sopchayu rivers, as well as samples of siltstones collected outside the Kara crater (rivers Halmeryu, Sayakha, Putyu, Anaroga and the creek Lavovyi). The samples were used for preparing polished thin sections and powder specimens for analytical works. Methods. Field observations, optical and electron scanning microscopy, and silicate analysis by the wet chemical method. Results and conclusions. The structural-textural and petrochemical features of the matrix, fragments of impact glasses, and lithoclasts of suevites from the B. Vanuyta river were characterized. The suevite matrix was found to exhibit an intensely sintered character and to be presented by feldspar, quartz, calcite, chlorite, muscovite, glauconite, and titanite. Lithoclasts include siltstones, sandstones, limestones, mudstones, and shales. Vitroclasts are characterized by angular and irregular morphology with different border patterns, and spotted, fluid, and porous textures. The similarity of the chemical composition of siltstone clusters and similar target rocks confirms the genetic relationship and the leading role of this type of target rocks in the formation of the studied suevites. The proximity in the composition of the impact glasses of the studied suevites and the glasses of type I and II suevites indicates the formation of suevite vitroclasts in the river B. Vanuyta by a similar protolith – siltstones and a clay component of the limestones. The matrix lithification character, morphology and nature of the vitroclast outlines indicate that the suevites from the B. Vanuyta river are the rocks of an aerodynamic facies formed under relatively high-temperature conditions, which structurally lie at the lower part of the detrital impactites sequence of the aerodynamic facies. The studied rocks are close to the type I suevites by the composition of the protolith and differ in the conditions of their formation. With the type II suevites, they have similar facies characteristics, but differ in the composition of the target rocks fragments. It is determined that the leading factor in the typification of suevites from the Kara astrobleme is the chemical composition, at the same time, the types can be subdivided more fractionally based on the specifics of the facies environments of their formation.

Impact-related chemical modifications of the Chang’E-5 lunar regolith

Impact events on the Moon have been recognized as modifying the composition of surface materials through processes such as shock metamorphism and mixing with exotic components. Previous studies have indicated that the regolith sampled by the Chinese Chang’E-5 mission was primarily evolved from local mare basalts, likely originating from a single episode of effusive volcanism. The relatively simple and monotonic protolith of the Chang’E-5 regolith presents a unique opportunity to investigate the chemical modifications induced by impact events. In this study, we conducted detailed petrographic and mineralogical analyses on a diverse set of lunar regolith samples, including thirty-three small impact glass particles (39–227 μm), one large agglutinate (∼1.6 mm), and sixteen basaltic clasts (0.1–1.6 mm). Numerical modeling was also conducted to quantitatively assess the melting behavior of basaltic clasts under different impact conditions. Our primary objective was to evaluate the chemical variations of impact glass in relation to lithic clasts. While the majority of homogeneous impact glass spherules and larger basaltic clasts (≥1 mm) exhibit similar bulk compositions (e.g., Al2O3, CaO and FeO) to the local regolith, we recognize additional effects of impact processes, including impact comminution, impact melting and crystallization, differential volatilization, and potentially selective melting. These processes have modified the texture and geochemistry of lunar regolith components. The chemical signatures of small clasts in the Chang’E-5 regolith indicate that the fine size fractions (e.g., those with diameters of ≤ 300 μm) are predominantly composed of lithic and monomineralic fragments with a substantial proportion being dominated by mesostasis. Melting of these sub-millimeter fractions may lead to the formation of impact glass with chemical compositions deviating from the average local regolith. These results have implications for understanding the compositional evolution of the Chang’E-5 regolith. Notably, our study suggests that impact glasses spherules with different major (e.g., TiO2, MgO) and minor (e.g., REEs, Zr, Th and U) element compositions could be derived from the same protolith of local mare basalts, instead of being exclusively attributed to exotic impact ejecta. In this case, small-scale local impacts may have played a crucial role in the impact history of the Chang'E-5 landing site.