¹Noriyuki KAWASAKI,²Daiki YAMAMOTO,³Sohei WADA,¹Changkun PARK,³Hwayoung KIM,⁴Naoya SAKAMOTO,^1,4Hisayoshi YURIMOTO
Meteoritics & Planetary Science (in Press) Link to Article [doi: 10.1111/maps.13989]
¹Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
²Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
³Division of Earth-System Sciences, Korea Polar Research Institute, Incheon, Republic of Korea
⁴Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo, Japan
Published by arrangement with John Wiley & Sons

Al–Mg mineral isochron studies using secondary ion mass spectrometry (SIMS)have revealed the initial26Al/27Al ratios, (26Al/27Al)0, for individual Ca-Al-rich inclusions(CAIs) in meteorites. We find that the relative sensitivity factors of27Al/24Mg ratio forSIMS analysis of hibonite, one of the major constituent minerals of CAIs, exhibit variationsbased on their chemical compositions. This underscores the critical need for usingappropriate hibonite standards to obtain accurate Al-Mg data. We measured the AlMgmineral isochron for hibonite in a fine-grained CAI (FGI) from the Northwest Africa 8613reduced CV chondrite by SIMS using synthesized hibonite standards with27Al/24Mg of~30,~100, and~400. The obtained mineral isochron of hibonite in the FGI yields (26Al/27Al)0of(4.730.09)9105, which is identical to that previously obtained from the mineralisochron of spinel and melilite in the same FGI (Kawasaki et al., 2020). The uncertainties of(26Al/27Al)0indicate that the constituent minerals in the FGI formed within~0.02 Myr inthe earliest solar system. The disequilibrium O-isotope distributions of the minerals in theFGI suggest that the O-isotope compositions of the nebular gas from which they condensedunderwent a transitional change from16O-rich to16O-poor within~0.02 Myr in the earliestsolar system. Once formed, the FGI may have been removed from the forming regionwithin~0.02 Myr and transported to the accretion region of the parent body.

¹M. Fastelli,²B. Schmitt,²P. Beck,²O. Poch,¹A. Zucchini,¹F. Frondini,¹P. Comodi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115633]
¹Department of Physics and Geology, University of Perugia, I-06123 Perugia, Italy
²Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
Copyright Elsevier

We analyse the quantitative effects of viewing geometry variations on the near-infrared reflectance spectra of mascagnite-(NH4)2SO4 and salammoniac-NH4Cl samples. Bi-directional reflectance spectra are collected in the 1–4.2 μm range considering a set of 3 incidence (i) angles (i = 0°; 30°; 60°) and 9 emergence (e) angles between −70° and 70° at room temperature and computed with respect to the normal direction. The NH4+ overtone and combinations bands located at ~1.09, 1.32, 1.62, 2.04, 2.2 and 3.05 μm are experimentally investigated. The bidirectional reflectance spectra of these samples show significant variations with the observation geometry in terms of reflectance values, spectral slope, and absorption bands parameters. The band positions remain essentially unchanged by varying the incident and emergence angles. On the other hand, bands’ area and depth show the highest variability for i ≥ 30° and e greater than ±40°(up to a factor 2.3 in relative mean variation). The area and depth parameters of these bands show a dual behaviour: (i) for the weak-medium spectral features below 2 μm the area and depth decrease as the phase angle increases. (ii) The strong spectral features above 2 μm increase their values only at phase angles above 90°, but also at low phase angles for high incidences, i ≥ 30°. This behaviour is linked both to the non-linear radiative transfer in particulate media and to the way the band depth and area are defined, relative to the local continuum. We observe important dependence (up to ~60% relative mean variation) of band depth and area on the incidence angle, up to 60°, compared to moderate variation with emergence angles (up to ~20% relative mean variation). Furthermore, the ~3 μm features becomes more saturated at ±70° emergence angles. A general trend of spectral bluing with change in observation geometry is observed. The current dataset is a contribution in the framework of present and future space missions focused on understanding the nature and quantification of ammonium-bearing minerals on icy bodies. The NH4+ − bearing minerals identification could provide information on: (i) ocean/brine compositions, (ii) possible explanations of geological phenomena and (iii) implications for biological activity.

¹C.P. Haupt,¹C.J. Renggli,¹M. Klaver,¹E.S. Steenstra,¹J. Berndt,¹A. Rohrbach,¹S. Klemme
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115625]
¹Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Münster 48149, Germany
Copyright Elsevier

The origin of young Chang’e 5 (CE5) lunar basalts is highly debated. We present results from high-pressure, high-temperature (P-T) phase equilibria experiments, and from petrological modeling, to constrain the depth and temperature of the source of these unique mare basalts. The experimental results indicate that the CE5 basalts could have formed either by melting clinopyroxene and Fesingle bondTi oxide-rich cumulates in the shallow lunar mantle, or by extreme fractional crystallization of a hot Mg-rich parental melt. Our findings corroborate the local preservation of significant heat (of at least 1200 °C) in the lunar mantle that is needed to generate basaltic melts of CE5 compositions at 2 Ga. We argue that the CE5 basalts are most likely formed by melting of Fe and Ti-rich cumulates in the shallow lunar mantle as extreme fractional crystallization of olivine and plagioclase from picritic parental melts requires too high temperatures in the lunar mantle (> 1500 °C) at ~2 Ga.