SPECTROSCOPY, MINERALOGY, AND GEOCHEMISTRY OF REGOLITH FROM GAIRÍA CALDERA (FUERTEVENTURA, SPAIN): AQUEOUS ALTERATION IN A DRY, SPARSELY VEGETATED, MAFIC MARS ANALOG SETTING

Aqueous minerals identified via orbiter- and rover-based investigation of Mars provide evidence of a complex history of liquid water. Unraveling this history and associated climatic conditions of the martian past is challenged by the difficulty in conclusive interpretation of the geochemical environments responsible for the observed mineral assemblages. Fortunately, study of analogous geological and climatic settings on Earth yields a wealth of information on geochemical processes producing similar assemblages of phyllosilicates and associated alteration minerals. The volcanic island of Fuerteventura (Canary Islands, Spain) offers an opportunity to investigate alteration and phyllosilicate formation in Mars-like environments. Like Mars, landscapes on much of Fuerteventura are characterized by volcanic landforms of a predominantly mafic origin, while prevailing environmental conditions include minimal precipitation, strong winds, and minimal or absent vegetation. In this study, we conduct a spectroscopy- and geochemistry-based investigation of Holocene ash and tephra collected from surface and near-surface environments on and near the Gairía Caldera of Fuerteventura. Ash, tephra, outcrop rock, and soil-like material collected here exhibit variations in color, spectral properties, mineralogy, and elemental abundances. Visible/near-infrared (VNIR) and mid-IR spectral analyses of orange and light brown materials have higher reflectance values plus stronger bands attributed to phyllosilicates (including features near 1.41, 1.91, 2.21, and 2.76 µm characteristic of montmorillonite) compared with the darker black/brown materials. These darker samples display a much broader band at ~3 µm, consistent with volcanic glass. Major oxide data illustrate similar distinctions between the lighter and darker samples. For samples across a transect of the caldera, SiO₂ content is ~42–43 wt. %, but lighter-colored samples show elevated Al₂O₃ and depleted Fe₂O₃, MgO, CaO, and Na₂O, attributed to alteration. Coordinated analyses of chemistry and mineralogy for different environments at Gairía Caldera may enable understanding of phyllosilicate formation in this dry and windy volcanic environment and may constrain formation of phyllosilicates under similar conditions on Mars.