Magmatic precipitation as a possible origin of Noachian clays on Mars

• Published in: Nature geoscience Vol. 5; no. 10; pp. 739 - 743
• Main Authors: Meunier, Alain, Petit, Sabine, Ehlmann, Bethany L., Dudoignon, Patrick, Westall, Frances, Mas, Antoine, El Albani, Abderrazak, Ferrage, Eric
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.10.2012; Nature Publishing Group
• Subjects: 704/106; 704/2151/209; 704/2151/330; 704/445/845; Atolls; Clay minerals; Degassing; Earth and Environmental Science; Earth Sciences; Earth System Sciences; Geochemistry; Geology; Geophysics/Geodesy; Iron; Lava; Magnesium; Mars; Mars climate; Mars spectra; Mars surface; Mars weather; Meteorite impacts on Mars; Precipitation; Sciences of the Universe; Weathering on Mars; ISE, Pacific, French Polynesia; ISE, Pacific, French Polynesia, Tuamotu Archipelago, Mururoa Atoll
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/ngeo1572

Hydrous clay minerals detected on the surface of Mars have been interpreted as indicators of the hydrologic and climatic evolution of the planet. The iron- and magnesium-rich clays described in thick, extensive outcrops of Noachian crust have been proposed to originate from aqueous weathering. This would imply that liquid water was stable at the surface of early Mars, presumably when the climate was warmer and wetter. Here we show that iron- and magnesium-rich clays can alternatively form by direct precipitation from residual, water-rich magma-derived fluids. Infrared reflectance spectra from terrestrial lavas from the Mururoa Atoll (French Polynesia) that underwent this precipitation process are similar to those measured for the Noachian crust. Such an origin is also consistent with the D/H ratio of iron- and magnesium-rich clays in some martian meteorites and the widespread presence of these clays in massive basaltic lavas, breccias and regolith. We propose that the progressive degassing of the martian interior over time and the resultant increasingly water-poor magmatic fluids—and not a cooling climate—may explain the absence of clays in Hesperian-aged and more recent formations. Hydrous clay minerals detected on the ancient martian crust have been proposed to have formed by aqueous weathering on a warm, wet early Mars. However, analyses of terrestrial clay minerals and comparisons to Mars suggest that the Noachian clays could have alternatively formed by precipitation from magmatic fluids.