¹A.-M.Seydoux-Guillaume,²T.de Resseguier,³G.Montagnac,⁴S.Reynaud,⁵H.Leroux,³B.Reynard,⁶A.J.Cavosie
Earth and Planetary Science Letters 595, 117727 Link to Article [https://doi.org/10.1016/j.epsl.2022.117727]
¹Univ Lyon, UJM, UCBL, ENSL, CNRS, LGL-TPE, F-42023 Saint Etienne, France
²PPRIME, CNRS-ENSMA-Université de Poitiers, 1 avenue Clément Ader, 86961 Futuroscope, France
³Univ Lyon, ENSL, UCBL, UJM, CNRS, LGL-TPE, F-69007 Lyon, France
⁴Université de Lyon, UJM-Saint-Etienne, CNRS, Institut d’Optique Graduate School, Laboratoire Hubert Curien UMR 5516, F-42023 Saint-Etienne, France
⁵Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et Transformations, F-59000 Lille, France
⁶The Space Science and Technology Centre (SSTC) and the Institute for Geoscience Research (TIGeR), School of Earth and Planetary Science, Curtin University, Perth, WA 6102, Australia
Copyright Elsevier

Impact-related damage in minerals and rocks provides key evidence to identify impact structures, and deformation of U-Th-minerals in target rocks, such as monazite, makes possible precise dating and determination of pressure-temperature conditions for impact events. Here a laser-driven shock experiment using a high-energy laser pulse of ns-order duration was carried out on a natural monazite crystal to compare experimentally produced shock-deformation microstructures with those observed in naturally shocked monazite. Deformation microstructures from regions that may have experienced up to ∼50 GPa and 1000 °C were characterized using Raman spectroscopy and transmission electron microscopy. Experimental results were compared with nanoscale observations of deformation microstructures found in naturally shocked monazite from the Vredefort impact structure (South Africa). Raman-band broadening observed between unshocked and shocked monazite, responsible for a variation of ∼3 cm−1 in the FWHM, is interpreted to result from the competition between shock-induced distortion of the lattice, and post-shock annealing. At nanoscale, three main plastic deformation structures were found in both naturally and experimentally shocked monazite: deformation twins, mosaïcism, and deformation bands. The element Ca is enriched along host-twin boundaries, which further confirms that the laser shock loading experiment produced both comparable styles of crystal-plastic deformation, and also localized element mobility, as that found in natural shock-deformed monazite. Deformation twins form in the experiment were only along the (001) plane, an orientation which is not considered diagnostic of shock deformation. However, both mosaïcism and deformation, expressed in SAED patterns as streaking of spots, and the presence of extra spots (more or less pronounced), are interpreted as unambiguous nano-scale signatures of shock metamorphism in monazite. Experimentally calibrated deformation features, such as those documented here at TEM-scale, provide new tools for identifying evidence of shock deformation in natural samples.

¹Maryjo Brounce,²Jeremy W.Boyce,²Francis M.McCubbin
Earth and Planetary Science Letters 595, 117784 Link to Article [https://doi.org/10.1016/j.epsl.2022.117784]
¹Department of Earth and Planetary Sciences, University of California Riverside, Riverside, CA 92521, USA
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
Copyright Elsevier

Estimates of the oxygen fugacity (fO2) recorded by the Martian nakhlite meteorites from direct observations of the main igneous phenocryst assemblages range from values similar to that recorded by the quartz-fayalite-magnetite oxygen buffer to ∼two orders of magnitude lower. Inferences of changes in fO2 during the late stages of crystallization, volcanic degassing, and emplacement of the nakhlite cumulate pile have been made based on variable sulfide and apatite chemistry. We present S-XANES measurements of the oxidation state of sulfur in apatite and associated mesostasis glass in Nakhla to place direct constraints on the magnitude of changes in fO2 experienced by the Nakhla portion of the nakhlite cumulate pile during apatite crystallization. Nakhla apatites range from containing dominantly S2− to containing dominantly S6+. This, together with correlations between S2−, Cl, and FeO in the mesostasis glass near these apatites, suggest that our measurements capture directly the oxidation of the interstitial late-stage Nakhla magmas as the result of Cl-saturation and degassing. As the result of this degassing, at least part of the nakhlite cumulate pile experienced an increase in fO2 of ∼1.5–2.5 orders of magnitude during apatite crystallization and final mesostasis cooling. Based on these measurements, the sulfur oxidation states of apatites in the other nakhlite meteorites are predicted to range from exclusively S2−-bearing to exclusively S6+-bearing.