Tardi-magmatic iddingsite in the Martian Nakhlite NWA 817

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta Pub Date : 2025-03-15 DOI:10.1016/j.gca.2025.01.028

V. Megevand , J.-C. Viennet , C. Le Guillou , F. Guyot , S. Bernard

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Abstract

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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火星Nakhlite NWA 817中的塔尔迪-麦哲伦蝶啶石

被称为“iddingsite”的矿物组合已经在火星陨石中被描述过。在nakholite中，该组合主要由富铁/镁层状硅酸盐（如蛇纹石和蒙脱石）组成，在某些情况下与铁氧化物（如铁水合石、针铁矿或（钛）磁铁矿）和碳酸盐伴生，并在中间平衡中以斑块和细脉形式出现，或以脉状渗入橄榄石和斜辉石中。到目前为止，iddingsite通常被解释为（亚）地表水对已存在的硅酸盐进行低温（<150°C）蚀变的产物。在这里，我们报告了NWA 817剖面的岩石学研究结果，揭示了橄榄石为主的空穴脉具有对称的结构，其内部为云母-青瓷石组成，外部为非辉石-皂石组成。这些特征与冷却层序末期橄榄石减压裂缝中渗透残余岩浆流体的递进分异相一致。我们认为，这一残液在触发寄主橄榄石的氘蚀变（即岩浆冷却过程中的氧化蚀变）的同时，直接生成了铁云母-青瓷-层状硅酸盐，从而在橄榄石接触处形成了铁-非铁辉石-皂化石的蚀变锋。总的来说，不排除其他nakhlite（如Lafayette）可能经历了火星表面水（亚）的二次蚀变的可能性，本研究中报告的观察结果更指向NWA 817 iddingsite的迟发岩浆生产。

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来源期刊

Geochimica et Cosmochimica Acta 地学-地球化学与地球物理

CiteScore

9.60

自引率

14.00%

发文量

437

审稿时长

6 months

期刊介绍： Geochimica et Cosmochimica Acta publishes research papers in a wide range of subjects in terrestrial geochemistry, meteoritics, and planetary geochemistry. The scope of the journal includes: 1). Physical chemistry of gases, aqueous solutions, glasses, and crystalline solids 2). Igneous and metamorphic petrology 3). Chemical processes in the atmosphere, hydrosphere, biosphere, and lithosphere of the Earth 4). Organic geochemistry 5). Isotope geochemistry 6). Meteoritics and meteorite impacts 7). Lunar science; and 8). Planetary geochemistry.