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Publication - Dr Tim Tomkinson

    The Northwest Africa (NWA) 5790 meteorite

    A mesostasis-rich nakhlite with little or no Martian aqueous alteration


    Tomkinson, T, Lee, MR, Mark, DF, Dobson, KJ & Franchi, IA, 2015, ‘The Northwest Africa (NWA) 5790 meteorite: A mesostasis-rich nakhlite with little or no Martian aqueous alteration’. Meteoritics and Planetary Science, vol 50., pp. 287-304


    Northwest Africa (NWA) 5790 is the most recently discovered member of
    the nakhlite group. Its mineralogy differs from the other nakhlites with
    a high abundance mesostasis (38.1 ± 3.6 vol%) and scarcity of
    olivine (4.0 ± 2.2 vol%). Furthermore, zoning of augite
    phenocrysts, and other petrographic and chemical characteristics suggest
    that NWA 5790 samples the chilled margin of its parent lava flow/sill.
    NWA 5790 contains calcite and rare clay minerals that are evidence for
    its exposure to liquid water. The calcite forms a cement to coatings of
    dust on the outer surface of the find and extends into the interior of
    the meteorite within veins. The presence of microbial remains within the
    coating confirms that the dust and its carbonate cement are terrestrial
    in origin, consistent with the carbon and oxygen isotope composition of
    the calcite. The clay minerals are finely crystalline and comprise
    ~0.003 vol% of the meteorite. δD values of the clay minerals range
    from -212 ± 109‰ to -96 ± 132‰, and cannot
    be used to distinguish between a terrestrial or Martian origin. As
    petrographic results are also not definitive, we conclude that secondary
    minerals produced by Martian groundwaters are at best very rare within
    NWA 5790. The meteorite has therefore sampled a region of the lava
    flow/sill with little or no exposure to the aqueous solutions that
    altered other nakhlites. This isolation could relate to the scarcity of
    olivine in NWA 5790 because dissolution of olivine in other nakhlites by
    Martian groundwaters enhanced their porosity and permeability, and
    provided solutes for secondary minerals.

    Full details in the University publications repository