Yamato-793605, EET79001, and other presumed martian meteorites: Compositional clues to their origins

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We report new data on the bulk compositions of several martian meteorites, most notably the Y-793605 peridotite. We find that Y-793605 is remarkably similar in composition to the other shergottitic peridotites. ALH77005 and EET79001. This high degree of compositional uniformity, and analogy to terrestrial ultramafic cumulates, suggest that the three peridotites formed in the comparatively uniform early-middle (and thus deep) portion of a martian layered intrusion. Considering that the process of launching off Mars probably required that a prior impact excavated these originally deep materials to positions closer to the surface, their compositional uniformity seems improbable, unless they were originally launched as a single mass that shortly thereafter underwent a secondary collisional fragmentation in the asteroid belt. We interpret "A" lithology of EET79001 as more likely to be an endogenously produced mixed magma than an impact melt. Our results indicate that Au is only slightly enriched in EET79001-A, compared to EET79001-B. The EET79001-A lithophile element composition can only be roughly approximated by modeling it as a mixture of EET79001-B plus any known variety of shergottitic peridotite, and the Au contents of martian meteorites (in general) are highly diverse. The presence of only two grossly dissimilar rock types (EET79001-B and EET79001-"X") as discernible components in EET79001-A seems an unlikely outcome from the chaotic process of impact mixing. Moreover, in general, it seems improbable that one of only 12 martian meteorites would be an impact melt of relatively young age.
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Yamato-793605, EET79001, and other presumed martian meteorites: Compositional clues to their origins

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