The mineralogy, petrology, and composition of anomalous eucrite Emmaville

1T. J. Barrett, 2D. W. Mittlefehldt, 1R. C. Greenwood, 1B. L. A. Charlier, 1S. J. Hammond, 2,3D. K. Ross, 1M. Anand, 1I. A. Franchi, 1F. A. J. Abernethy, 1M. M. Grady
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12818]
1School of Physical Sciences, The Open University, Milton Keynes, UK
2Astromaterials Research Office, NASA Johnson Space Center, Houston, Texas, USA
3UTEP and Jacobs Technology, Houston, Texas, USA
4Department of Earth Sciences, Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

The Emmaville eucrite is a relatively poorly studied basaltic achondrite with an anomalous oxygen isotope signature. In this study, we report comprehensive mineralogical, petrographic, and geochemical data from Emmaville in order to understand its petrogenesis and relationship with the basaltic eucrites. Emmaville is an unusually fine-grained, hornfelsic-textured metabasalt with pervasive impact melt veins and mineral compositions similar to those of typical basaltic eucrites. The major and trace element bulk composition of Emmaville is also typical of a basaltic eucrite. Three separated individual lithologies were also analyzed for O isotopes; a dark gray fraction (E1), a shocked lithology (E2), and a lighter gray portion (E3). Fractions E1 and E2 shared similar O isotope compositions to the bulk sample (E-B), whereas the lighter gray portion (E3) is slightly elevated in Δ17O and significantly elevated in δ18O compared to bulk. No evidence for any exogenous material is observed in the thin sections, coupled with the striking compositional similarity to typical basaltic eucrites, appears to preclude a simple impact-mixing hypothesis. The O-isotopes of Emmaville are similar to those of Bunburra Rockhole, A-881394, and EET 92023, and thus distinct from the majority of the HEDs, despite having similarities in petrology, mineral, and bulk compositions. It would, therefore, seem plausible that all four of these samples are derived from a single HED-like parent body that is isotopically distinct from that of the HEDs (Vesta) but similar in composition.

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