FUMAROLIC ALTERATION ON MARS: LESSONS LEARNED FROM TERRESTRIAL ANALOG FIELDWORK

Hydrothermal vents appear to be prime targets for understanding the appearance of Life on Earth, and to search for ancient Life elsewhere in the Universe (e.g. [1,2]). On Earth, plate tectonics destroyed most surface rocks formed within the first ~1 billion years, limiting our ability to provide constraints on planetary habitability at the time Life developed. In contrast, Mars has been much less tectonically active, and large outcrops of ancient rocks, including hydrothermal vents, are preserved and accessible on the surface [3]. The first definitive evidence for continental vents on Mars is the in-situ detection of amorphous silica-rich outcrops (>90% wt opal-A) by the Mars Exploration Rover Spirit, tentatively interpreted as either acid sulfate leaching in fumarolic environments or direct precipitation from hot springs [4,5]. Multiple detections of hydrated minerals made from orbit, such as amorphous silica in Valles Marineris [6,7] have also been interpreted as the products of volcanic hydrothermal alteration, although their definitive identification is more difficult at the orbital scale.

The identification and interpretation of hydrated mineral assemblages, within ancient aqueous environments on Mars, are key to the evolution of the Martian surface and its past habitability. To contribute to the identification of fumarole and hot spring deposits on Mars, we surveyed their mineral assemblages at a few terrestrial analog sites: the Solfatara Volcano (Campania, Italy), and Pico Alto Volcano and Furnas Volcano (Azores archipelago, Portugal). Several mineral identification techniques (VNIR and Raman spectroscopy, XRD) were used in the field and in the lab, and their individual merit was assessed. Characterization of the collected rock samples revealed a variety of mineralogical assemblages and alteration patterns at the three sites, which are best explained by the influence of temperature, bedrock composition and texture, and possibly the duration of hydrothermal activity.

References:

[1] Nisbet & Sleep (2001) Nature, 409, 1083-1091. [2] Da Silva et al. (2015) J. Mol. Evol., 2015, 80, 86. [3] Carr & Head (2010) EPSL, 294, 185-203. [4] Ruff et al. (2011) JGR, 116, E00F23. [5] Squyres et al. (2008) Science, 320, 1063-1067. [6] Thollot et al. (2012) JGR, 117, E11. [7] Milliken, et al. (2008) Geology, 36, 847-850.