^1,2,3J.S.Gorce,^1,2D.W.Mittlefehldt,²J.I.Simon
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.034]
¹Lunar and Planetary Institute, USRA, TX 77058, USA
²Center for Isotope Cosmochemistry and Geochronology, Astromaterials Research Office, NASA/Johnson Space Center, Houston, TX 77058, USA
³Rensselaer Polytechnic Institute, Department of Earth and Environmental Science, Troy, NY 12180
Copyright Elsevier

Eucrites exhibit a range of igneous and metamorphic textures and geochemistries that can be used to study the evolution of early planetary differentiation and crust formation in the solar system. We integrated petrologic/textural observations, in-situ geochemical analyses, and thermodynamic modeling to explore the petrogenesis of Elephant Moraine (EET) 90020, an unbrecciated meteorite. We identified microdomains that record relatively high metamorphic temperatures and concluded that diffusion processes likely modified EET 90020 during and/or after peak thermal conditions. There is little evidence that partial melting caused the distribution of minor and trace elements within or among the microdomains. Trace element linear transect measurements within the microdomains imply that phosphate minerals strongly controlled trace element distributions throughout the sample. The discrepancy between the observed metamorphic textures, major element chemistry, and the trace element distributions is a consequence of differing chemical mobility. Multiple processes are influencing geochemistry within a single sample which has implications for the development of petrogenetic models that seek to reconcile the differences observed between eucrite geochemical groups.

¹Wei Yang et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.08.030]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Copyright Elsevier

Lunar impact glasses can provide important information on the bulk compositions of their sources and the impact history of the Moon. Here, we report the chemical composition of fifty-four clean glass spherules containing neither relict clasts nor crystals from the Chang’e-5 (CE5) regolith. They can be subdivided into three compositional groups: (1) mid-Ti basaltic (TiO2 = 4.1∼6.5 wt.%), (2) low-Ti basaltic (TiO2 = 1.3∼3.9 wt.%), and (3) high-Al (Al2O3 >15 wt.%). Fifty-one glasses (∼94%) are mid-Ti basaltic, which form a loose compositional cluster for most major and trace elements. These glasses exhibit considerable variations in SiO2 (35.3∼45.3 wt.%). Their TiO2, Al2O3, MgO and CaO show negative correlations with SiO2, while the Na2O, K2O and P2O5 positively correlate with SiO2, also yielding a positive correlation between the CIPW normative plagioclase and olivine. These variations likely result from differential vaporization of SiO2, strongly suggesting an impact origin of these glasses. Their major and trace element compositions are averagely similar to the bulk-rock, in turn indicating that they were formed from the local regolith. The remaining three glasses, including two low-Ti basaltic and one high-Al variety, exhibit distinct major and trace elements from the regolith, indicating an exotic source. In addition, the mid-Ti basaltic glasses provide another approach for estimating the average composition of the CE5 basalt other than directly measuring the small basalt fragments assuming that the exotic materials in the CE5 regolith were limited. This estimation reveals critical trace element characteristics of the CE5 basalt, e.g., it has higher La/Yb (3.71), Sm/Yb (1.76), Sr/Yb (31.6), and (Eu/Eu*)N (0.45) than KREEP, indicating that CE5 basalt must derive from a non-KREEP source. Chemical modeling indicates that the contribution of KREEP-rich materials in the mantle source should be less than 0.3%. The trace element characteristics of the CE5 basalt can be reproduced by extensive (80%) fractional crystallization after low-degree (2%) melting. We propose that this fractional crystallization process might occur at depth, implying vast igneous underplating (7250∼11750 km3) beneath the CE5 landing area. This study also suggests that the high Th concentration (5.43 ppm) is an inherent property of the CE5 basalt resulting from extensive fractional crystallization. Thus, high Th detected by remote sensing may not be associated directly with a KREEP component but rather with highly fractionated basalts.

¹Christophe Drouet,²Matteo Loche,²Sébastien Fabre,²Pierre-Yves Meslin
American Mineralogist 107, 1807-1817 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2022/Abstracts/AM107P1807.pdf]
¹CIRIMAT, Université de Toulouse, CNRS, Toulouse INP, UPS, 4 allée Emile Monso, 31030 Toulouse, France
²Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, UPS, CNRS, CNES, 9 Avenue du Colonel Roche, 31400 Toulouse, France
Copyright: The Mineralogical Society of America

Jahnsites/whiteites are a large family of phosphate hydrate minerals of relevance to terrestrial and
martian mineralogy. It was recently hypothesized as being present in Gale Crater sediments from XRD
analyses performed by the CheMin analyzer aboard the Curiosity rover. However, the conditions of
formation and thermodynamic properties of these compounds are essentially unknown. In this work,
we have optimized the ThermAP predictive thermodynamic approach to the analysis of these phases,
allowing us to estimate for the first time the standard formation enthalpy (ΔHf°), Gibbs free energy
(ΔGf°), and entropy (S°) of 15 jahnsite/whiteite end-member compositions, as well as of related phases
such as segelerite and alluaudites. These estimations were then used to feed speciation/phase diagram
calculation tools to evaluate the relative ease of formation and stability of these hydrated minerals,
including considering present martian conditions. Selected laboratory experiments confirmed calcula-
tion outcomes. All of our data suggest that the formation of jahnsites is an unlikely process, and point
instead to the formation of other simpler phosphate compounds. The stability domain, as calculated
here, also raises serious questions about the possible presence of jahnsites on Mars as in Gale Crater,
which appears rather improbable.

^1,2Niccolò Satta,³Masaaki Miyahara,⁴Shin Ozawa,²Hauke Marquardt,⁵Masahiko Nishijima,⁶Tomoko Arai,⁴Eiji Ohtani
American Mineralogist 107, 1661-1667 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2022/Abstracts/AM107P1661.pdf]

¹Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth 95440, Germany
²Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, U.K.
³Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
⁴Department of Earth Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
⁵Laboratory for Protein Crystallography and Laboratory for Electron Structural Biology Institute for Protein Research, Osaka University, Suita-shi Osaka 565-0871, Japan
⁶Planetary Exploration Research Center, Chiba Institute of Technology, Chiba 275-0016, Japan
Copyright: The Mineralogical Society of America

The Apollo 15 mission returned various samples of regolith breccias, typical lunar rocks lithified
by impact events on the Moon’s surface. Here we report our observations on shock features recorded
in a section of the Apollo Sample 15299. We observe the presence of ferropericlase crystals confined
in a shock-melt pocket and conclude that their formation is related to a shock-induced incongruent
melting of olivine. While predicted by experiments, this phenomenon has never been observed in a
natural sample. The incongruent melting of olivine provides an important signature of melting under
high-pressure conditions and allows for estimating the pressure-temperature (P-T) experienced by the
studied sample during the impact event. We infer that the fracture porosity that likely characterized the
studied sample prior to the shock event critically affected the P-T path during the shock compression
and allowed the studied sample to be subjected to elevated temperature during relatively low shock
pressures.