MAGMAS BETWEEN TWO WORLDS: A COMPARISON OF MARTIAN AND TERRESTRIAL PARENT MELT COMPOSITIONS FROM PRIMARY MELT INCLUSIONS HOSTED IN NAKHLITES AND TERRESTRIAL MAFIC ANALOGS

Primary melt inclusions represent preserved products of parent melts entrapped within crystallizing host minerals in cooling magmas and serve as useful indicators for determining the compositions and evolution of magmas within igneous bodies. While several recent studies have investigated melt inclusions in terrestrial samples or Martian samples, there is currently a lack of research providing direct comparisons of Martian and Earth parent melts through inclusion compositional analyses.

For this study, we have selected two nakhlites (clinopyroxene-rich Martian meteorites) and seven terrestrial mafic rocks with mineralogies similar to nakhlites. The major and minor compositions of the identified and targeted primary melt inclusions were determined through in-situ quantitative and semi-quantitative analyses (scanning electron microscopy, field emission electron probe microanalysis with wavelength dispersive spectroscopy (FE-EPMA-WDS), and Raman spectroscopy), and subsequently modeled (MELTS/Petrolog-3 software) to re-calculate the parent melt composition and conditions present during entrapment.

From our analyses, we found that nakhlite melt inclusion content largely differs internally between nakhlites and externally between melt inclusions found in terrestrial analogs. Our sample of nakhlite NWA 13669 contains a large (~300 μm) fayalite-hosted polymineralic, devitrified melt inclusion with albite-composition glass, pyroxene microlites, Ti-magnetite, and apatite. Inclusions from our terrestrial samples are average-sized (20-50 μm) and mostly silica-rich glass with few to no child crystals, with the exception of inclusions from one of our pyroxenite samples (pyroxene microlites within carbonate-rich glass) and from our peridotite sample (magnesite-composition glass). In nakhlite NWA 11013, we studied a small (~16 μm) augite-hosted basaltic glassy inclusion that does not match the composition of terrestrial inclusions. Both nakhlite and terrestrial inclusions show similar element spatial distributions, as revealed by WDS maps. This suggests that Martian magma is compositionally unique from terrestrial analog magmas, though the diffusion of major and minor elements and nucleation of pyroxene child crystals seems consistent across Martian and terrestrial magmas.