¹PengYue Wang, ² Edward Cloutis, ¹Ye Su, ³PengFei Zhang
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116320]
¹State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
²Department of Geography, University of Winnipeg, Winnipeg, Canada
³Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
Copyright Elsevier

The establishment of robust meteorite-asteroid links has been a major focus of planetary exploration, and a major driver of asteroid sample return missions. Reflectance spectroscopy has been shown to be a powerful tool for this purpose. For the meteorites dominated by silicate minerals, quantitative analysis of spectral absorption features caused by the Fe2+-bearing minerals (mainly olivine and pyroxene) is a common method to determine mafic silicate mineralogy and end member abundances, and establish the relationship between them and possible parent bodies. In this study, the reflectance spectra of 22 primitive achondrites (acapulcoites, lodranites and winonaites) from NASA RELAB database were analyzed to determine their positions in the plot of the band area ratio (BAR) and 1 μm band center (Band I center). We found that Band I center and BAR of acapulcoites and lodranites are in roughly the same range. Acapulcoite-lodranite partially overlap with the field of H chondrites in the plot of the BAR and Band I center. This overlap means that spectral calibrations (also referred to as mineralogical formulas) based on the two types of meteorites needs to be applied with caution. The 2 μm band center of acapulcoite–lodranite is significantly lower than that of H chondrites, which is consistent with the conclusion of previous studies and provides a means to separate these two groups. In addition, the choice of spectral parameter analysis techniques may be a potential error source in similar studies. We provide generalized spectral fields of primitive achondrites in the plot of the BAR and Band I center derived from two widely used technologies.

^1,2,3Pierre-Marie Zanetta et al.  (>10)
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.09.021]
¹CNRS, Université Jean Monnet Saint-Étienne, ENS de Lyon, LGL-TPE, UMR5276, F-42023 Saint-Etienne, France
²Aix-Marseille Université, CNRS, IRD, INRAE, CEREGE, 13545 Aix-en-Provence, France
³Mineral Analysis Laboratory of SODEMI, 31, Bd des Martyrs, Abidjan-Cocody, 01 BP 2816, Abidjan 01, Cote d’Ivoire
Copyright Elsevier

Tektites are reduced (Fe2+) glasses formed by the quenching of molten material ejected from Earth’s surface as a result of a hypervelocity impact. The vast majority of tektites are usually homogeneous glasses, but rare samples containing mineral inclusions can provide insights about the source material, sample thermal history, and tektite formation process. Tektites from two distinct strewn fields presenting Ca-phosphate inclusions detected from anomalous magnetic susceptibility were studied: one sample from the Ivory Coast tektite (ICT) field ejected at 1.07 Ma from the Bosumtwi crater (10.5 km in size) in Ghana and two Muong Nong type samples from the Australasian tektite field (MN-AAT) ejected at 0.79 Ma from a crater possibly situated in southeast Asia. In ICT, Ca-phosphate inclusions are systematically embedded in lechatelierite (SiO2 glass). In MN-AAT Ca-phosphate are either embedded in lechatelierite or in Fe-rich glass forming schlieren. Multiscale petrographic characterization using correlative microscopy associating scanning electron microscopy, microprobe and, transmission electron microscopy reveals that rounded inclusions in ivoirite are composed of acicular Ca-phosphates (merrillite) embedded in an amorphous P-rich glass. In MN-AAT, inclusions consist mostly of single droplets of Fe-Mg rich Ca-phosphate (structurally related to apatite), but few droplets often forming an emulsion texture show a complex assemblage of apatite, magnetite, pyroxene, and spinel growing from a Pt-rich nucleus. Diffusion profile around lechatelierite domains reveals maximum temperatures greater than 2200–2400 °C in the impact plume of the Australasian tektite and the Ivory coast tektite. Heating time is of the order of seconds-tens of seconds rather than minutes as previously suggested (20 s for MN-AANT and 5 s for ICT). The number, the density, and the fact that inclusions are entirely crystallized in MN-AAT support relatively slow cooling rates (<200 °C/h), in comparison with the faster cooling rates (>2000 °C/h) indicated by the precipitation of amorphous P-rich glass in ICT. In both impact events, ejecta that had been heated to high temperatures did not remain in the vapor plume for an extended period of time and landed rapidly (within tens of seconds) at a relatively high temperature (>1000 °C) on the Earth’s surface.

Phosphate inclusions systematically embedded in lechatelierite in ICT provide clues about the source material. It suggests that the parent material for these silica-rich inclusions is not conventional detrital quartz. Rather, parts of lechatelierite domains may be inherited from a biogenic source that could be consistent with tropical soil (source of the phosphor) and its biomass (silica of plant origin). The reduction process that tektites record during their formation may be explained by superficial material since forests can contain a sizable mass of carbon that can reduce iron in tektites and produce platinoid-rich metallic nuclei and the Fe3+/ΣFe gradient recorded by the dendritic spinels.