Tardi-magmatic precipitation of Martian Fe/Mg-rich clay minerals via igneous differentiation
Résumé
Mars is seen as a basalt covered world that has been extensively altered through hydrothermal or near surface water-rock interactions. As a result, all the Fe/Mg-rich clay minerals detected from orbit so far have been interpreted as secondary, i.e. as products of aqueous alteration of pre-existing silicates by (sub)surface water. Based on the fine scale petrographic study of the evolved mesostasis of the Nakhla meteorite, we report here the presence of primary Fe/Mg-rich clay minerals that directly precipitated from a water-rich fluid exsolved from the Cl-rich parental melt of nakhlites during igneous differentiation. Such a tardi-magmatic precipitation of clay minerals requires much lower amounts of water compared to production via aqueous alteration. Although primary Fe/Mg-rich clay minerals are minor phases in Nakhla, the contribution of such a process to Martian clay formation may have been quite significant during the Noachian given that Noachian magmas were richer in H2O. In any case, the present discovery justifies a re-evaluation of the exact origin of the clay minerals detected on Mars so far, with potential consequences for our vision of the early magmatic and climatic histories of Mars.
Domaines
Physique [physics] Matière Condensée [cond-mat] Science des matériaux [cond-mat.mtrl-sci] Chimie Matériaux Physique [physics] Physique [physics] Géophysique [physics.geo-ph] Planète et Univers [physics] Astrophysique [astro-ph] Physique [physics] Astrophysique [astro-ph] Planète et Univers [physics] Sciences de la Terre
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