Lithology A in EETA79001 - Product of impact melting on Mars

Mittlefehldt, D. W.; Lindstrom, D. J.; Lindstrom, M. M.; Martinez, R. R.
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Conference Paper, 28th Annual Lunar and Planetary Science Conference, p. 961.

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Martian meteorite EETA79001 is composed of two distinct magmatic lithologies, astutely named A and B, joined by an igneous contact. Lithology B is a coarse-grained, ferroan basalt, while lithology A is both finer-grained and more magnesian. In addition, lithology A contains xenocrysts and xenoliths of olivine, orthopyroxene and chromite, which are petrologically similar to the major phases in Martian lherzolites such as ALHA77005. A petrologic model to explain the petrographic and major element composition of lithology A is that it is a mixed magma composed of basalt like lithology B with a magma similar in composition to the Martian lherzolites. We have refined this magma-mixing model for lithology by folding trace element data into the mixing calculations. We have performed micro-INAA on xenocryst-free groundmass samples drilled from thin section, and have begun petrologic and geochemical studies of additional samples of EETA79001, including xenocryst samples, and ALHA77005. We concur that lithology A is a mixed lithology, but we believe that it is an impact melt. Lithology B is a large basalt xenolith in the impact melt.