Article Dans Une Revue Geochimica et Cosmochimica Acta Année : 2025

Tardi-magmatic iddingsite in the Martian Nakhlite NWA 817

Résumé

The mineral assemblage referred to as "iddingsite" has been described in Martian meteorites. In Nakhlites, this assemblage is mainly composed of Fe/Mg-rich phyllosilicates (such as serpentine and smectites) associated in some cases with Fe-oxides (such as ferrihydrite, goethite or (titano)magnetite) and carbonates, and occurs either as patches and veinlets in the mesostasis or as veins infiltrating olivines and clinopyroxenes. So far, iddingsite has usually been interpreted as a product of low-temperature (<150 • C) alteration of pre-existing silicates by (sub) surface water. Here, we report results of the petrographic study of a section of NWA 817 revealing that the olivine-hosted iddingsite veins are symmetrically structured with an internal part exhibiting a mica-celadonite composition and an external part displaying a nontronite-saponite composition. These features are consistent with a progressive differentiation of a residual magmatic fluid having infiltrated decompression-induced cracks of olivines at the end of the cooling sequence. We propose that this residual liquid directly produced the ferric mica-celadonite phyllosilicates while triggering the deuteric alteration of the hosting olivine (i.e. oxidative alteration during magma cooling), thereby producing an alteration front made of Fe-nontronite-saponite at the contact with olivine. Altogether, without excluding the possibility that other Nakhlites (such as Lafayette) may have experienced secondary alteration by (sub)surface Martian water, the observations reported in the present study rather point to the tardi-magmatic production of iddingsite in NWA 817.

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hal-04932266 , version 1 (06-02-2025)

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Valentine Megevand, J-C Viennet, C Le Guillou, F Guyot, S Bernard. Tardi-magmatic iddingsite in the Martian Nakhlite NWA 817. Geochimica et Cosmochimica Acta, 2025, ⟨10.1016/j.gca.2025.01.028⟩. ⟨hal-04932266⟩
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