Impact-generated hydrothermal alteration on Mars: clay minerals, oxides, zeolites, and more
Notice bibliographique
Résumé
In the Noachian, Mars’ crust was deeply affected by impact crater gardening, and subsequent hydrothermal alteration. While water was present in the Martian crust, frequent impacts provided prominent heat sources that drove hydrothermal systems. Those systems were scattered randomly over the planet’s surface and variable in size, but generally spanned the diameter of any ≥10 km complex crater. These systems were also deep reaching and long-lived with central crater uplifts and crater modification zones affected by the most intense water flow. Because circulating water driven by a temperature gradient changes the thermochemical status of a system, mineralogical reactions inevitably took place. Similar mineralogical consequences have been documented in terrestrial impact-generated hydothermal systems. Approximately half of all known impact structures on Earth show hydrous alteration phases produced by the interaction of water with a melt sheet and/or hydrothermal systems that penetrated the crust beneath the crater floor. Immense systems have been documented in drill cores from Earth’s largest impact structures, such as the Chicxulub crater (Yucatán, Mexico) and the Sudbury structure (Ontario, Canada). As we have shown earlier for the basaltic crust of Mars, thermochemical changes caused by circulation of heated formation brines mainly result in the crystallization of sheet silicates (serpentine, chlorite, nontronite, and kaolinite), amphiboles, oxides and hydroxides (magnetite, hematite, diaspore), and additional minor phases. Our results compare favorably with those from sattelite-based spectroscopic measurements of the Martian surface by OMEGA and CRISM (aboard the European Mars Express and U.S. Mars Reconnaissance Orbiter, respectively). They report many of the same minerals, amongst them several smectites and micas – such as kaolinite, Fe/Mgsmectite, saponite, illite/muscovite, and chlorite – but also hydrous silica, zeolite, and carbonate. Potential testimony of impact-generated hydrothermal systems has been found in three Martian craters so far: hydrous phases are located in central peaks and inner crater walls in a ~100 km diameter crater in Mawrth Vallis, a crater of similar size in Terra Meridiani, and an ~20 km diameter crater in the Western Isidis region. In addition to producing mineral assemblages similar to those being observed on Mars, our calculations constrain formation conditions. Our results suggest that alteration assemblages are largely controlled by the water to rock ratio (W/R) and temperature, while the pH is bufferd by the precipitating and dissolved species. Our previous studies showed that three sheet silicates, which also have been found on Mars (chlorite, nontronite, kaolinite), point to specific formation conditions: Chlorite is indicative of intermediate to low W/R and occurs over the whole temperature range. The clay minerals nontronite and kaolinite indicate intermediate and high W/R, respectively. Moreover, nontronite forms below 250 °C only. While our previous studies focussed on the parameters pressure, temperature, and W/R, in this study we explore the influence of host rock variability on the resulting alteration assemblages.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,001 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,001 | 0,002 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».