¹Briony Horgan et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2022JE007612]
¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West 19 Lafayette, IN 47906
Published by arrangement with John Wiley & Sons

The first samples collected by the Perseverance rover on the Mars 2020 mission were from 60 the Maaz formation, a lava plain that covers most of the floor of Jezero crater. Laboratory 61 analysis of these samples back on Earth would provide important constraints on the petrologic 62 history, aqueous processes, and timing of key events in Jezero crater. However, interpreting 63 these samples requires a detailed understanding of the emplacement and modification history of 64 the Maaz formation. Here we synthesize rover and orbital remote sensing data to link outcrop-65 scale interpretations to the broader history of the crater, including Mastcam-Z mosaics and 66 multispectral images, SuperCam chemistry and reflectance point spectra, RIMFAX ground 67 penetrating radar, and orbital hyperspectral reflectance and high-resolution images. We show 68 that the Maaz formation is composed of a series of distinct members corresponding to basaltic to 69 basaltic-andesite lava flows. The members exhibit variable spectral signatures dominated by 70 high-Ca pyroxene, Fe-bearing feldspar, and hematite, which can be tied directly to igneous 71 grains and altered matrix in abrasion patches. Spectral variations correlate with morphological 72 variations, from recessive layers that produce a regolith lag in lower Maaz, to weathered 73 polygonally fractured paleosurfaces and crater-retaining massive blocky hummocks in upper 74 Maaz. The Maaz members were likely separated by one or more extended periods of time, and 75 were subjected to variable erosion, burial, exhumation, weathering, and tectonic modification. 76 The two unique samples from the Maaz formation are representative of this diversity, and 77 together will provide an important geochronological framework for the history of Jezero crater.

^1,2Jean-Alix Barrat,³Addi Bischoff,⁴Brigitte Zanda
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.07.003]
¹Univ Brest, CNRS, UMR 6539 (Laboratoire des Sciences de l’Environnement Marin), Institut Universitaire Européen de la Mer (IUEM), Place Nicolas Copernic, 29280 Plouzané, France
²Institut Universitaire de France, Paris
³Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany
⁴Muséum National d’Histoire Naturelle, Laboratoire de Minéralogie et de Cosmochimie du Muséum, CNRS UMR7202, 61 rue Buffon, 75005 Paris, France
Copyright Elsevier

We report on new trace element analyses of enstatite chondrites (ECs) to clarify their behavior during the metamorphism. During the transition from a type 3 to a type 5 or higher, silicates lose a large portion of their trace elements to sulfides. Our procedure allows us to obtain trace element abundances of the silicate fraction of an EC quite easily. The element patterns of these fractions (especially REE patterns) are quite different for EH and EL chondrites, and are furthermore dependent on the metamorphic grade. This procedure can be usefull to classify meteorites, in particular when the sulfides are altered. Applied to anomalous ECs, it allows direct recognition of the EH affinity of QUE 94204, and suggests that Zakłodzie, NWA 4301, and NWA 4799 derive from the same EH-like body of previously unsampled composition.

We have used the concentrations obtained on the silicate fractions of the most metamorphosed chondrites to discuss the chemical characteristics of the primitive mantles of reduced bodies of EH or EL affinity (i.e., after core segregation). Our data indicate that these mantles are very depleted in refractory lithophile elements (RLEs), particularly in rare earth elements (REEs), and notably show significant positive anomalies in Sr, Zr, Hf, and Ti. These estimates imply that the cores contain most of the REEs, U and Th of these bodies. Interestingly, the inferred primitive mantles of these reduced bodies contrast with that of the Earth. If the Earth accreted essentially from ECs, one would expect similar signatures to be preserved, which is not the case. This mismatch can be explained either by a later homogenization of the bulk silicate Earth, or alternatively, that the materials that were accreted were isotopically similar to ECs, but mineralogically different (i.e., oldhamite-free).