Impact Reactivation of a Hydrothermal System in Basalt in the Vargeão Dome Impact Structure, Brazil

Abstract As hydrous minerals have been observed in impact craters on Mars, impact‐generated hydrothermal systems (IGHSs) have been considered as potential habitats for life on that planet. The Vargeão Dome, a 12 km wide impact structure in southern Brazil, was formed in basalts with at least two hydrothermal alteration stages. This structure is a rare terrestrial analog for IGHS evolution on Mars. However, the thermochemical evolution of these stages and their relationship to the impact remain unresolved. Two vein‐forming alteration stages were identified by multidisciplinary sample analysis of Vargeão Dome. Fractured and deformed white vein fragments from the first stage occur within red veins from the second. This suggests reactivation of the white vein set during the crater excavation and modification stages. Rare Earth Element and Rb‐Sr isotope data indicate different fluid sources for the white and red veins and an evolving fluid system. Thermodynamic modeling indicates a cooling sequence from 100–250 to