From the Colorado Plateau to Beyond Earth: Using Magmatic Intrusions into Sulfate-rich Sediments as Analogue for Planetary Habitable Environments

Baharier, Bea (2025). From the Colorado Plateau to Beyond Earth: Using Magmatic Intrusions into Sulfate-rich Sediments as Analogue for Planetary Habitable Environments. Doctor of Philosophy (PhD) thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00102675

Abstract

Life appeared on Earth ~3.8 Ga, during a time when Earth and Mars shared a similar geological history. Unlike Earth, Mars became increasingly hostile to life, losing most of its atmosphere and surface water, with weathering potentially dominated by sulfuric acid. If life ever evolved on Mars, hypothetical microbes would have needed to shelter in the subsurface, or within isolated sulfur-rich hydrothermal environments, or within evaporite minerals. Consequently, researching sulfur-rich hydrothermal relics on Earth is instrumental in understanding potential life on Mars. This study investigated the relics of a plausible sulfur-rich hydrothermal habitat formed by the interaction between 'Awesome Dike' (AD) and sulfate-rich sediment from the San Rafael Swell, Utah, USA. Field investigations and geochemical laboratory analyses were conducted to model the fluid-rock interaction, understand past hydrothermal conditions, and assess the fluid's habitability potential. AD alteration was limited to calcite pseudomorphs with minor amounts of Fe-Mg-rich clays, Ca sulfate veinlets, and veins. The pseudomorph morphology and previous work on other local intrusions point to kaersutite amphibole as the likely precursor. The contact zone exhibited three alteration zones, with sulfates partially absent for the first 15 cm from the dike and no extensive alteration observed 2 meters away, indicative of localised sulfate fluid migration towards AD. Thermochemical modeling of the alteration indicated that the fluids began as high-temperature, acidic H₂O-CO₂ fluid, gradually neutralising to an HCO₃ rich composition. As the fluid mixed with the dissolved sulfate from the sediments, it became enriched with CaSO₄, forming a subsurface-isolated sulfate-rich hydrothermal environment and eventually evaporite minerals. The fluids eventually cooled to habitable conditions as indicated by the detection of gypsum, and the fluid conditions may have formed past and present viable habitats. This study emphasises the importance of understanding small-scale alterations and fluid composition of the interface of sedimentary rocks with magma. It suggests that the search for past biosignatures and potential extant habitats in Martian relic hydrothermal systems by magmatic intrusions is a promising target for astrobiology research.

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