Hydrothermal alteration at the basalt-hosted Vista Alegre impact structure, Brazil

1Jitse Alsemgeest,1Fraukje M. Brouwer,2Luis F. Auqué,3Natalia Hauser,3Wolf Uwe Reimold
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13763]
1Geology and Geochemistry Cluster, Faculty of Science, Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081HV The Netherlands
2Department of Geosciences, University of Zaragoza, Calle Pedro Cerbuna 12, Zaragoza, 50009 Spain
3Laboratory of Geochronology and Isotope Geochemistry, Geosciences Institute, University of Brasília, Brasília, DF, CEP 70910-900 Brazil
Published by arrangement with John Wiley & Sons

Hydrothermal systems provide a possible habitat for early life and are key targets in the quest for life outside Earth. In impact craters on Mars, hydrous minerals can represent products of impact-generated hydrothermal systems (IGHS) or minerals already present in the crust and exposed during impact-caused excavation. Because of its basaltic target rock, similar in composition to Martian crust, the Vista Alegre impact structure in Brazil is one of the very few analog structures that may reveal the origin of these minerals, if evidence of hydrothermal alteration is established. This work presents the results of a systematic search for evidence of hydrothermal alteration at the Vista Alegre impact structure. Four types of alteration were identified, all within a 2.5–3.0 km radius from the crater center: a zircon-bearing melt veinlet, two sets of hydrothermal veins consisting predominantly of calcite and chabazite, and local alteration comprising saponite. Thermodynamic modeling suggests subsequent heating and cooling for each of the hydrothermal vein sets. Combined thermodynamic and spectrometric evidence indicates that development of a vigorous IGHS is unlikely. If similar processes occur on Mars, hydrous minerals are more likely preimpact phases exposed by excavation, rather than being formed through an IGHS.

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