Mineral paragenesis on Mars: The roles of reactive surface area and diffusion

1,2Alberto G. Fairén,1Carolina Gil-Lozano,3Esther R. Uceda,4Elisabeth Losa-Adams,5Alfonso F. Davila,4Luis Gago-Duport
Journal of Geophysical Research, Planets (in Press) Link to Article [DOI: 10.1002/2016JE005229]
1Centro de Astrobiología (CSIC-INTA), Madrid, Spain
2Department of Astronomy, Cornell University, Ithaca, NY, USA
3Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco Madrid, Spain
4Departamento de Geociencias Marinas, Universidad de Vigo, Lagoas Marcosende, Vigo, Spain
5NASA Ames Research Center, Moffett Field, CA, USA
Published by arrangement with John Wiley & Sons

Geochemical models of secondary mineral precipitation on Mars generally assume semi-open systems (open to the atmosphere but closed at the water-sediment interface) and equilibrium conditions. However, in natural multicomponent systems, the reactive surface area of primary minerals controls the dissolution rate and affects the precipitation sequences of secondary phases; and simultaneously the transport of dissolved species may occur through the atmosphere-water and water-sediment interfaces. Here we present a suite of geochemical models designed to analyze the formation of secondary minerals in basaltic sediments on Mars, evaluating the role of (i) reactive surface areas and (ii) the transport of ions through a basalt sediment column. We consider fully open conditions, both to the atmosphere and to the sediment, and a kinetic approach for mineral dissolution and precipitation. Our models consider a geochemical scenario constituted by a basin (i.e., a shallow lake) where supersaturation is generated by evaporation/cooling, and the starting point is a solution in equilibrium with basaltic sediments. Our results show that cation removal by diffusion, along with the input of atmospheric volatiles and the influence of the reactive surface area of primary minerals, play a central role in the evolution of the secondary mineral sequences formed. We conclude that precipitation of evaporites finds more restrictions in basaltic sediments of small grain size than in basaltic sediments of greater grain size.

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