AQUEOUS ALTERATION AT MARS ANALOGUE SITES: GEOCHEMISTRY AND MINERALOGY OF SEDIMENT FROM THE DRY VALLEYS (ANTARCTICA), FUERTEVENTURA (SPAIN), AND THE MOJAVE DESERT (USA)

The search for liquid water—and its implications for life—has been the driving question for exploration of Mars for six decades. Orbiter and rover investigations of the martian surface have revealed mineralogical suites including associations of chlorides, sulfates, and phyllosilicates, which together indicate a complex (and ofttimes enigmatic) history of liquid water. Yet, the proper understanding of this aqueous history is crucial to understanding past and/or present habitability of Mars. Therefore, understanding processes that may result in formation of such aqueous mineral assemblages is essential. Here, we study terrestrial localities that share numerous characteristics with Mars’s surface and/or with inferred martian paleoenvironments. We performed spectroscopic, mineralogical, and geochemical investigations (using tools similar to those employed in studies of the martian surface) of sediment retrieved from three Mars analogue localities on Earth: a transient brine pond in Antarctica’s xeric Wright Valley, Fuerteventura’s basaltic Gairía Caldera in the Canary Islands, and the dry but seasonally endorheic Koehn Lake of California’s Mojave Desert. Chemical weathering and alteration products found in the sediments include closely associated (but distinct) horizons of surficial salts, a poorly crystalline clay-like layer, and deeper gypsiferous sediment developed under intermittently evaporitic conditions at the Antarctic brine pond. Al-phyllosilicates developed via aqueous alteration (including activity of an ephemeral stream) of mafic material are found at Gairía Caldera. Visible salt crusts composed of gypsum, silica, and clays formed in a playa setting in the Mojave Desert. These analogue sites provide compelling examples of settings where volcanic materials are chemically altered to salts, clays, and/or sulfates under different aqueous conditions, and provide insight into environments that may explain aqueous mineral assemblages observed on Mars.