Effect of hot desert weathering on the bulk-rock iron isotope composition of
L6 and H5 ordinary chondrites

Authors

  • Gaëlle SAUNIER,

    1. Laboratoire d’Étude des Mécanismes de Transfert en Géologie, Université de Toulouse, Centre National de la Recherche Scientifique, IRD, 14, avenue Edouard Belin, 31400 Toulouse, France
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  • Franck POITRASSON,

    Corresponding author
    1. Laboratoire d’Étude des Mécanismes de Transfert en Géologie, Université de Toulouse, Centre National de la Recherche Scientifique, IRD, 14, avenue Edouard Belin, 31400 Toulouse, France
      Corresponding author. E-mail: Franck.Poitrasson@lmtg.obs-mip.fr
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  • Bertrand MOINE,

    1. Département de Géologie, Faculté des Sciences, Université Jean Monnet, 23 Avenue du Docteur P. Michelon, 42023 St-Etienne, France
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  • Michel GREGOIRE,

    1. Laboratoire Dynamique Terrestre et Planétaire, Centre National de la Recherche Scientifique, Université de Toulouse, CNES, 14, avenue Edouard Belin, 31400 Toulouse, France
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  • Abdelmadjid SEDDIKI

    1. Laboratoire de Magmatisme et Synthèse Géodynamique des Bassins Algériens, Université d’Oran Es-senia, BP. 1524,
      Oran 3 1000, Algérie
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Corresponding author. E-mail: Franck.Poitrasson@lmtg.obs-mip.fr

Abstract

Abstract– Although iron isotopes are increasingly used for meteorites studies, no attempt has been made to evaluate the effect of terrestrial weathering on this isotopic tracer. We have thus conducted a petrographic, chemical, and iron isotopic study of equilibrated ordinary chondrites (OC) recovered from hot Moroccan and Algerian Saharan deserts environment. As previously noticed, we observe that terrestrial desertic weathering is characterized by the oxidation of Fe-Ni metal (Fe0), sulfide and Fe2+ occurring in olivine and pyroxene. It produces Fe-oxides and oxyhydroxides that partially replace metal, sulfide grains and also fill fractures. The bulk chemical compositions of the ordinary chondrites studied show a strong Sr and Ba enrichment and a S depletion during weathering. Bulk meteoritic iron isotope compositions are well correlated with the degree of weathering and S, Sr, and Ba contents. Most weathered chondrites display the heaviest isotopic composition, by up to 0.1‰, which is of similar magnitude to the isotopic variations resulting from meteorite parent bodies’ formation and evolution. This is probably due to the release of isotopically light Fe2+ to waters on the Earth’s surface. Hence, when subtle Fe isotopic effects have to be studied in chondrites, meteorites with weathering grade above W2 should be avoided.

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