How do secondary iron enrichments form within basaltic eucrites? An experimental approach

1Stella Rombeck,1Christian Vollmer,2Julia Roszjar,3Adam R. Sarafian,1Stephan Klemme
Meteoritics & Planetary Science (in Press) Link to Article []
1Institut für Mineralogie, Westfälische Wilhelms‐Universität Münster, Corrensstrasse 24, 48149 Münster, Germany
2Department of Mineralogy and Petrography, Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria
3Corning Incorporated, Science and Technology Division, 21 Lynn Morse Rd., Painted Post, New York, 14870 USA
Published by arrangement with John Wiley & Sons

Some basaltic eucrites and basaltic lithologies in howardites derived from the asteroid 4 Vesta exhibit unusual secondary veinlet textures consisting mostly of fayalitic olivine and Fe‐enrichments within pyroxenes. Recent studies discussed the formation of these Fe‐rich phases either by interaction with a vapor and/or liquid phase (metasomatism), or by a high‐temperature melting process. We therefore performed a series of heating and hydrothermal experiments with liquids of different compositions on natural pyroxene crystals (augite and orthopyroxene) to evaluate these contrasting hypotheses. The results of the heating experiments show that incongruent melting of pyroxenes at about 1070 °C causes textures that are very similar to those observed in the meteorites. We conclude that a part of the natural secondary veins might be explained by heating processes at similar temperatures. The hydrothermal experiments with aqueous liquids of different Fe‐enriched compositions clearly indicate ion exchange reactions resulting in partial Fe‐enrichments of the pyroxene. Interestingly, these Fe‐enrichments occurred independent of the Fe content of the liquid, which can be explained by an internal origin of Fe from the pyroxenes. In one hydrothermal experiment of augite with Fe‐oxalate solution, deposition of fayalitic olivine was observed. From our experimental observations, we conclude that aqueous liquids are plausible candidates for explaining the deposition of Fe‐enrichments and fayalitic olivine inside the fractures of pyroxene. However, we cannot rule out a high‐temperature melting process slightly above the peritectic point of pyroxene to explain a fraction of observed secondary Fe‐enrichments.


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