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Río Tinto sedimentary mineral assemblages: A terrestrial perspective that suggests some formation pathways of phyllosilicates on Mars |
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| Authors: | DC Fernández-Remolar O Prieto-Ballesteros M Fernández-Sampedro M Gailhanou |
| Institution: | a Centro de Astrobiología (INTA-CSIC), Ctra Ajalvir km 4, 28850 Torrejón de Ardoz, Spain b ESCET, Área de Geología, Universidad Rey Juan Carlos, 28933 Móstoles, Spain c inXitu Inc., 2551 Casey Avenue, Suite A, Mountain View, CA 94043, USA d TECSEN, UMR CNRS 6122, Université Paul Cézanne, 13397 Marseille, France e Centro de Biología Molecular Severo Ochoa (UAM-CSIC), Cantoblanco, 28049 Madrid, Spain |
| Abstract: | The presence of extensive phyllosilicate deposits from the early Noachian of Mars are often interpreted as having formed from neutral to subalkaline solutions. In this paper we examine the Río Tinto fluvial basin, an early Mars analog, that hosts clay production and sedimentation along the entire course of the river. At Río Tinto, phyllosilicate minerals including clays and micas are sourced by volcanosedimentary bedrock of rhyolitic and andesitic composition affected by Carboniferous hydrothermal alteration. Pleistocene to modern acidic weathering of those materials chemically altered the volcanic and sedimentary materials to K/Na-clay-(montmorillonite/smectites)-kaolinite assemblages in paleosoils and fractures while physical weathering degrades phyllosilicates more resistant to acidic attack. During the wet season, phyllosilicates are eroded, transported and deposited from both acidic headwaters and neutral tributaries. During the dry season, sulfates and nanophase oxyhydroxides co-precipitate. Late summer storms that cause fast flooding events mix illite, quartz, feldspars, iron oxides and other minerals in fluvial deposits where these minerals are stabilized and aggrade until the following wet season. As a result, chemical precipitates, primary phyllosilicates and secondary clays form mineral admixtures that explain the compositional diversity of the fluvial deposits. These deposits reveal the persistence of smectites, whose occurrence is explained given that the reaction kinetics under acidic conditions of degradation is lowered by seasonal discharges of the river. The longevity of phyllosilicate minerals within fluvial deposits depends on climatic and geochemical conditions and processes which are in turn are correlated to temperature, persistence of water, hydrological cycling, hydrogeochemistry and composition of the source materials in the basement. These parameters are universal and have to be characterized in order to understand the distribution of mineral composition on any planetary surface, including Mars. |
| Keywords: | Earth Mineralogy Mars |
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