Meteoritics & Planetary Science最新文献

This study presents a comprehensive analysis of the mineralogical, geochemical properties, and in situ Sr-Nd-Pb isotopic systematics of a newly discovered unbrecciated lunar basaltic meteorite NWA 14526 (NWA refers to northwest Africa). Bulk composition derived through both mineral modes and impact melt vein classifies NWA 14526 as a low-Ti, low-Al, and low-K mare basalt. In situ Pb isotopic analyses define a Pb–Pb isochron yielding an age of 3009 ± 43 Ma, representing the meteorite's crystallization age. In situ Rb-Sr isotopic analyses of plagioclase and maskelynite provide an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.69969 ± 0.00024 (2σ), while phosphate and mesostasis in situ Sm-Nd analyses yield an initial εNd value of +10.7 ± 2.1 (2σ). Although NWA 14526 shares comparable mineralogical, bulk-rock composition, and Sr isotopic characteristics with contemporaneous lunar basaltic meteorites (NWA 4734, LAP 02205, NWA 14137, and NWA 10597), its significantly elevated εNd values preclude genetic pairing with these specimens. Isotopic modeling indicates minimal KREEP component contribution (<0.5%) in its mantle source. Our compilation of lunar Sr-Nd isotopic data reveals two distinct evolutionary trends corresponding to depleted lunar mantle and urKREEP reservoirs, respectively. Notably, no temporal correlation between basalt source KREEP enrichment and eruption age is observed, suggesting that the KREEP component did not necessarily play a decisive role in driving late-stage lunar magmatism and volcanism.

We report on the mineralogy, petrography, and oxygen and aluminum-magnesium isotopic systematics of the corundum-bearing Ca,Al-rich inclusions (CAIs) from the CK3 (Karoonda-type) carbonaceous chondrites NWA (Northwest Africa) 4964-#1 and -Homer, NWA 5343-#1, and LAR (Larkman Nunatak) 12002-#1. These CAIs experienced extensive metasomatic alteration: melilite and possibly anorthite and AlTi-diopside are nearly completely replaced by secondary corundum, grossular, CaNa-plagioclase, FeAl-diopside, and FeO-rich spinel; perovskite is largely replaced by ilmenite. Two types of corundum grains occur in the NWA 4964 CAIs: (1) compact, FeO-poor grains zoned in cathodoluminescent (CL) images and (2) FeO-bearing (up to 1.5 wt% FeO), porous grains showing no detectable CL; the porous corundum grains overgrow the compact ones. Corundum grains in CAIs from LAR 12002 and NWA 5343 belong to the first and second types, respectively. Hibonite, primary spinel, and rare perovskite inclusions in spinel retained the original, ¹⁶O-rich compositions (Δ¹⁷O ~ −24 ± 2‰), whereas melilite, most perovskite grains, and secondary corundum and spinel are ¹⁶O-depleted (Δ¹⁷O ~ −5 ± 2‰). Hibonite and melilite have excesses of radiogenic ²⁶Mg (²⁶Mg*) corresponding to approximately the canonical initial ²⁶Al/²⁷Al ratio [(²⁶Al/²⁷Al)₀] of ~5 × 10⁻⁵ suggesting that corundum-bearing CAIs studied belong to a population of the canonical inclusions, dominant in most chondrite groups. Corundum grains in LAR 12002-#1, NWA 4964-#1, NWA 4964-Homer, and NWA 5343-#1 show resolvable ²⁶Mg* correlated with ²⁷Al/²⁴Mg ratio which corresponds to much lower than the canonical (²⁶Al/²⁷Al)₀: (3.10 ± 0.48) × 10⁻⁶, (3.03 ± 0.23) × 10⁻⁶, (2.72 ± 0.19) × 10⁻⁶, and (3.5 ± 1.2) × 10⁻⁷, respectively. Porous Fe-bearing corundum grains in NWA 4964 CAIs Homer and #1 have low ²⁶Mg* not correlated with ²⁷Al/²⁴Mg ratio. We conclude that compact corundum grains in the CK3 CAIs studied are secondary parent body products that resulted from metasomatic alteration of the host inclusions by hydrothermal fluid ~3−5 Ma after their crystallization. Porous corundum grains may have formed by dehydration of diaspore [AlO(OH)] during subsequent thermal metamorphism.

Löpönvaara is a rare new phosphorus-rich iron meteorite find from Löpönvaara, Finland. The ~164 g meteorite was discovered in 2017 from the same area as the ungrouped Lieksa pallasite. Löpönvaara was classified as an ungrouped iron meteorite due to its unusually high concentration of P (>4 wt%), coupled with a moderate concentration of Ni (~11 wt%), and Ga–Ge abundances in the “III” range. The meteorite consists of ~75 vol% kamacite and ~22 vol% schreibersite, with accessory troilite (<0.1 vol%), and minor terrestrial weathering products. The kamacite in Löpönvaara occurs as three different types: (1) rare, large 2–5 mm partially resorbed clasts; (2) round, ≤0.5 mm partially resorbed clasts; and (3) small, several tens of μm to sub-μm exsolution blebs and globules in the matrix. Schreibersite occurs solely as microscopic matrix material in between the type (1) and (2) kamacite clasts. The lack of taenite and the overall compositional and textural features of Löpönvaara suggest that it retained its composition possibly from a P-rich portion of immiscible melt at late stages of fractional crystallization, but its textural features suggest that the meteorite suffered impact-related metamorphism. The meteorite has no close textural or compositional affinities, which makes it unique and an important target for future studies.

Silica polymorphs in meteorites provide critical constraints on crystallization processes associated with thermal activity in the early solar system. A detailed investigation of silica polymorphs in eucrites (the largest group of achondrites) using cathodoluminescence imaging and laser-Raman spectroscopy revealed significant variations in the relative abundance of silica polymorphs. Based on these variations, the eucrites were divided into four “Si-groups” according to their dominant silica phase: Si-0 (cristobalite-dominant eucrites), Si-I (quartz-dominant eucrites), Si-II (quartz and tridymite-dominant eucrites), and Si-III (tridymite-dominant eucrites). In studied eucrites, tridymite and cristobalite form lathy euhedral shapes, while quartz is anhedral, coexistent with opaques and phosphates, suggesting that silica polymorphs were crystallized from different stages and formation processes. We propose a new model that explains the formation pathways of silica minerals in eucrites and accounts for the distinct formation histories represented by each Si-group: tridymite crystallizes from alkali-rich immiscible melts (starting at ≥ ~1060°C), cristobalite crystallizes from quenched melts (~1060°C), and quartz crystallizes from extremely differentiated melts and/or by solid-state transformation from tridymite and cristobalite through interactions with sulfur-rich vapor below ~1025°C. This model explains the occurrences of silica polymorphs in eucrites without requiring secondary heating or shock processes.

It has been proposed that IIE iron meteorites formed through impact processes on a parent body that was composed of either the H chondrites or a much-debated fourth ordinary chondrite group, the HH chondrites. To resolve this debate, we have compiled a large dataset for the ordinary chondrites, low-fayalite ungrouped chondrites, and IIE irons, and undertaken a statistical analysis to determine if: (1) the current classification of ordinary chondrite groups is statistically appropriate; and (2) the IIE irons are related to H chondrites or if they represent a distinct group that formed on a “HH” chondrite parent body. We demonstrate that the current classification system based on petrography and olivine and orthopyroxene chemistry is appropriate for the H, L, and LL chondrites. We define a fourth “F chondrite” group consisting of eight, previously ungrouped, very low-Fa Type 3 and 4 chondrites. Statistical analysis of Δ¹⁷O data alone cannot distinguish between the H chondrites and IIE irons, nor between the L and LL chondrites. Furthermore, statistical analyses are unable to distinguish H chondrites from IIE irons in all measures (mineral chemistry, chondrule size, bulk Δ¹⁷O, Ge and Mo isotopic compositions, and bulk siderophile element abundances in metal); there is no evidence for a “HH” chondrite group. These results are consistent with formation of IIE iron meteorites through impact melting and near-surface metal segregation on the H chondrite parent body. This genetic link between H chondrites and IIE irons allows us to understand the geochemical and petrological changes that occurred during planetary formation and evolution.

We report the first oxygen isotope measurements of tochilinite (δ¹⁷O: 11.0 ± 2.1‰, δ¹⁸O: 23.5 ± 4.0‰ and Δ¹⁷O: −1.1 ± 1.2‰) in a CM chondrite (Winchcombe, lithology C [CM2.2/2.3]). We analyzed type-I tochilinite-cronstedtite intergrowths (TCIs)—formed by pseudomorphic replacement of kamacite. Alongside T1 and T2 calcite and magnetite, these secondary phases define a linear trendline in δ¹⁷O-δ¹⁸O isotope space with a slope of 0.50, slightly shallower than the mass-dependent slope (0.52). This demonstrates that, in addition to dominant mass-dependent fractionation (controlled by mineral-specific and temperature-dependent equilibrium processes), mass-independent mixing between ¹⁶O-rich anhydrous silicates, and ¹⁶O-poor water influenced the evolving Δ¹⁷O composition of alteration fluids. Petrographic evidence shows tochilinite and T1 calcite formed early and are closely associated in the alteration sequence. Assuming isotopic equilibrium between these phases, we estimate formation temperatures of approximately 135°C and a δ¹⁸O_water value of 28‰. These findings align with previous hydrothermal synthesis experiments and underscore the value of multi-phase isotopic measurements for reconstructing the fluid history of chondritic parent bodies.

Numerous studies of basalt clasts in regolith samples returned by the Chang'E-5 (CE-5) mission have provided constraints on the timing and nature of the youngest magmatism on the Moon. However, there have been far fewer studies of breccias, one of the main constituents of regolith. Here, we present a comprehensive investigation of the mineralogy, petrology, and U-Pb geochronology of two CE-5 regolith breccia samples, which are composed of lithic clasts, agglutinates, glass particles, and mineral fragments. In contrast to the high level of maturity of CE-5 regolith, the regolith breccias are immature, as judged by their low agglutinate (~11 vol%) and moderate to low matrix contents (~49 vol%). The CE-5 regolith breccias comprise mainly mare (~90 vol%) and non-mare (~10 vol%) materials. A low-Ti mare component of late Imbrian to early Eratosthenian age is identified, in addition to the predominant late Eratosthenian basalts in mare components. Non-mare components include Mg-suite norite, highland impact melt clasts, glass particles, and minor fragmented minerals. The glass particles in the CE-5 regolith breccias are compositionally variable and can be divided into five types, that is, basaltic (mare), KREEP-rich, feldspathic (highland), Si-poor, and Si-K-rich glasses. Among these glasses, most (65%) are compositionally exotic to the site. The diverse provenance of these “exotic” materials in the CE-5 breccias is consistent with the multiple ages of Zr-bearing phases at 3.97–3.92 Ga, ~3.2 Ga, 2.93–2.40 Ga, and ~2.0 Ga, in which early Eratosthenian ages are reported for the first time from returned lunar samples. The contrast in the level of maturity and in glass composition between CE-5 regolith and regolith breccias can be reconciled if CE-5 regolith breccias represent an ancient soil and were excavated from a buried stratigraphic sequence by later impacts. The duration of exposure of this old soil was short (<250 Myr), and its maturation was interrupted by late Eratosthenian basaltic magmatism.

This paper presents the results of proton irradiation actions of three meteorites which were studied by LV-SEM, Raman spectroscopy, and FTIR spectroscopy methods, both before and after the artificial irradiations. The three samples are the Dhofar (Dho) 007 eucrite, the Northwest Africa (NWA) 4560 LL3.2, and the NWA 5838 H6 chondrite meteorites, which were irradiated by 1 keV average solar wind protons using the ECR ion source at ATOMKI with 10¹⁷ and 10¹⁹ ions cm⁻² fluence values. According to FTIR spectra, the first irradiation induced metastable alteration, and after the second irradiation, crystals organized into more stable phases. In the Dho 007 sample, the pyroxene shows a positive peak shift and FWHM change after the first irradiation, with decreased intensity of spectra. After the second irradiation, the peak position and FWHM decreased but showed an increase in comparison with the state before the irradiation in the FTIR spectra. The minor band near 620 cm⁻¹ disappeared after the irradiations in the FTIR spectra; however, the Raman spectra do not show the disappearance of minor bands. The olivine (in NWA 4560 and NWA 5838) and pyroxene (in Dho 007) showed negative peak shifts indicating escape of Mg²⁺ ions from the crystal lattice, together with positive peak shifts and increase of FWHM indicating amorphization of the crystal structure. Considering band shapes and intensities, both FTIR and Raman spectra showed decreasing intensity after the first irradiation, with possible metastable alteration. However, the spectra after the second irradiation show a moderate increase in FWHM change, which indicates a change in the crystal lattice. In the FTIR spectra, the minor band at 620 cm⁻¹ disappeared in the case of pyroxene.

Triple oxygen isotope analyses of meteorites are a fundamental tool for classifying meteorites and investigating early solar system processes. However, its utility can be significantly compromised by terrestrial oxygen contamination during weathering processes on Earth's surface. Aiming to restore the original bulk oxygen isotope composition of meteorites through the removal of terrestrial weathering products, leaching procedures with hydrochloric acid (HCl) or ethanolamine thioglycollate (EATG) are often employed, but their effects remain poorly understood. Therefore, here we obtained high-precision triple oxygen isotope data for a comprehensive set of meteorites to systematically evaluate the efficacy and consequences of these leaching methods as a function of meteorite group, weathering grade, petrologic type, and find/fall location and status. Our data for untreated and leached bulk meteorite powders show that leaching can cause shifts of several permil in ¹⁸O/¹⁶O and ¹⁷O/¹⁶O in aqueously altered and pristine chondrites, and lower magnitude shifts in thermally metamorphosed chondrites and achondrites. Though some shifts can be explained by removal of terrestrial weathering products, many suggest the inadvertent removal of indigenous phases. As such, this study highlights the benefits and disadvantages of leaching methods for meteorites, which can be best assessed by analyses of both untreated and HCl/EATG-leached aliquots.

While polar regions on Mars have long been recognized as primary reservoirs of ice, recent studies suggest that ice-rich deposits may also exist at lower latitudes due to cyclic variations in Martian climate. This study presents findings from geomorphological research conducted in the deepest region of Xanthe Terra, an unnamed impact crater. The objectives were to investigate the morphology and topography of the area to assess the occurrence of glacial features and to establish their potential age and geological context. We identified compelling evidence for fluvial and glacial activities within the crater by carefully analyzing various landforms, including theater-head valleys, layered terrains, fans, sinuous ridges, and viscous flows. The findings suggest a dynamic environment shaped by water and ice processes, likely influenced by an impact event approximately 3.5 billion years ago. The presence of Amazonian fan deposits dating back to approximately 750 million years ago further highlights the continued activity of fluvial processes in the region. Our study contributes to a deeper understanding of Mars' geological evolution and underscores the importance of further research to unravel the complex history of the planet's low-latitudinal regions and its changing environmental conditions over time.