Ancient Crustal Diversity Preserved within Martian Meteorite NWA 7034

Abstract:

The martian meteorite Northwest Africa (NWA) 7034 is a breccia containing a variety of igneous clasts and igneous derived mineral fragments suspended in a matrix of fine grained material. Igneous clasts were examined using electron probe microanalysis (major and minor element compositions), BSE images (modal mineralogy), and secondary ion mass spectrometry (REEs). The clasts contain minerals of similar composition to martian meteorites and surface rocks, although mineral abundances differ between these clasts and other martian rocks. The clasts vary in rock type and include basalt, andesite, trachyandesite, and an exotic phosphate and FeTi-oxide rich lithology that is more Fe-rich than Wishstone-class rocks analyzed by MER. Many of the basaltic clast compositions match those of Gusev Crater rocks, as well as the average composition of the martian crust determined from orbital data, providing a strong link between this meteorite and the martian crust. Furthermore, studies have shown the majority of igneous materials in this meteorite to be ~4.4 Ga (Yin et al., 2014; Nyquist et al., 2013, Tartèse et al., 2014); this suggests these clasts represent some of the earliest formed martian crust. The range in rock types contained within this meteorite suggest early Mars was capable of producing crust that was diverse in composition, chemically enriched, and oxidized (ΔFMQ +0.7 to +4), at least in local regions. The reason for the difference in chemistry between these ancient crustal rocks and the younger SNC meteorites remains to be determined, but the lithologic diversity recorded by NWA 7034 provides evidence for a petrologically diverse martian surface both spatially and temporally.