^1,2Rebecca N. Greenberger, ¹John F. Mustard, ^3,4,5Gordon R. Osinski, ^3,4,6Livio L. Tornabene, ^3,4,7Alexandra J. Pontefract, ^3,4Cassandra L. Marion, ^3,4Roberta L. Flemming, ⁸Janette H. Wilson, ⁹Edward A. Cloutis
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12716]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, Rhode Island, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
³Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, Canada
⁴Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
⁵Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada
⁶SETI Institute, Mountain View, California, USA
⁷Planetary Science Institute, Tucson, Arizona, USA
⁸Headwall Photonics, Inc., Fitchburg, Massachusetts, USA
⁹Department of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada
Published by arrangement with John Wiley & Sons

Meteorite impacts on Earth and Mars can generate hydrothermal systems that alter the primary mineralogies of rocks and provide suitable environments for microbial colonization. We investigate a calcite–marcasite-bearing vug at the ~23 km diameter Haughton impact structure, Devon Island, Nunavut, Canada, using imaging spectroscopy of the outcrop in the field (0.65–1.1 μm) and samples in the laboratory (0.4–2.5 μm), point spectroscopy (0.35–2.5 μm), major element chemistry, and X-ray diffraction analyses. The mineral assemblages mapped at the outcrop include marcasite; marcasite with minor gypsum and jarosite; fibroferrite and copiapite with minor gypsum and melanterite; gypsum, Fe3+ oxides, and jarosite; and calcite, gypsum, clay, microcline, and quartz. Hyperspectral mapping of alteration phases shows spatial patterns that illuminate changes in alteration conditions and formation of specific mineral phases. Marcasite formed from the postimpact hydrothermal system under reducing conditions, while subsequent weathering oxidized the marcasite at low temperatures and water/rock ratios. The acidic fluids resulting from the oxidation collected on flat-lying portions of the outcrop, precipitating fibroferrite + copiapite. That assemblage then likely dissolved, and the changing chemistry and pH resulting from interaction with the calcite-rich host rock formed gypsum-bearing red coatings. These results have implications for understanding water–rock interactions and habitabilities at this site and on Mars.

¹Doris Breuer, ¹Ana-Catalina Plesa, ^1,2Nicola Tosi, ¹Matthias Grott
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12727]
¹DLR, Institute of Planetary Research, Berlin, Germany
²Department of Astronomy and Astrophysics, Technische Universität Berlin, Berlin, Germany
Published by arrangement with John Wiley & Sons

Petrological analysis of the Martian meteorites suggests that rheologically significant amounts of water are present in the Martian mantle. A bulk mantle water content of at least a few tens of ppm is thus expected to be present despite the potentially efficient degassing during accretion, magma ocean solidification, and subsequent volcanism. We examine the dynamical consequences of different thermochemical evolution scenarios testing whether they can lead to the formation and preservation of mantle reservoirs, and compare model predictions with available data. First, the simplest scenario of a homogenous mantle that emerges when ignoring density changes caused by the extraction of partial melt is found to be inconsistent with the isotopic evidence for distinct reservoirs provided by the analysis of the Martian meteorites. In a second scenario, reservoirs can form as a result of partial melting that induces a density change in the depleted mantle with respect to its primordial composition. However, efficient mantle mixing prevents these reservoirs from being preserved until present unless they are located in the stagnant lid. Finally, reservoirs could be formed during fractional crystallization of a magma ocean. In this case, however, the mantle would likely end up being stably stratified as a result of the global overturn expected to accompany the fractional crystallization. Depending on the assumed density contrast, little secondary crust would be produced and the lithosphere would be extremely cool and dry, in contrast to observations. In summary, it is very challenging to obtain a self-consistent evolution scenario that satisfies all available constraints.