Séminaire Maxime Pineau

Date : 1 mars 2022 - 11 h 00 / 12 h 30

Catégories : Agenda, GP Géodynamique, Séminaires

Maxime Pineau (ATER à l'Université d'Orléans, ISTO) donnera, dans l'amphitéâtre de l'OSUC (E018), un séminaire intitulé : Near infrared spectral signature of opaline silica: a tool to decipher aqueous alteration at Mars.

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Résumé : "Orbital and in-situ data of Mars have shown numerous mineralogical evidences of past water-rock interactions at the surface. However, the physicochemical conditions in which these minerals were formed remain poorly understood. In particular, the relative roles of continental weathering and hydrothermal activity involved in their formation are still debated. Among the mineral phases observed on Mars, hydrated/opaline silica, or opal, is a common product of the alteration of silicates that can be considered as a mineralogical proxy to better constrain paleo-environmental conditions of the martian surface. Previous studies, based on the near-infrared (NIR) analysis of terrestrial varieties of hydrated silica, have shown that specific spectral criteria can provide information on the different types of silica, variations in their hydration behaviors, and the alteration processes that formed them. Applied to martian remote sensing data, the criteria show that hydrated silica is associated with two different geomorphological contexts on Mars: (i) hydrated and/or crystalline silica in aeolian deposits, and (ii) dehydrated and/or amorphous silica in outcrops. Furthermore, these criteria suggest that aeolian deposits could be detrital relicts of Si-rich hydrothermal deposits, and outcrops mostly derived from past continental weathering. Also, the current atmosphere of Mars can promote the non-systematic dehydration of silica and the transformation of structural liquid water into ice. Nevertheless, the results show that some martian sites, even though considered to have undergone hydrothermal activity, exhibit hydrated silica with spectral properties reminiscent of continental weathering. These observations question the existence of surface hydrothermal processes taking place at low temperatures (< 50°C). Sampled Icelandic geyser silica were categorized in nine distinct lithofacies. By comparing in-situ measured fluid temperatures and spectral properties of the samples, only the near-vent lithofacies possess a pure “hydrothermal signature”. Other samples, located in the distal areas of the geyser fields (i.e. low-T fluids) present NIR signatures close to those of opals formed by continental weathering. This observation pleads in favor of low-T hydrothermal activity for some of the Mars’ sites for which geomorphological study suggests geyser-like contexts."


Organisateur : ISTO

Adresse : Amphitéâtre, Observatoire des Sciences de l'Univers en région Centre (OSUC), Orléans, France