New triple oxygen isotope data of bulk and separated fractions from SNC meteorites: Evidence for mantle homogeneity of Mars

1,2Arshad Ali, 1Iffat Jabeen, 3David Gregory, 4Robert Verish,1Neil R. Banerjee
1Department of Earth Sciences & Centre for Planetary Science and Exploration, Western University, London, Ontario, Canada
2Earth Sciences Research Centre (ESRC), Sultan Qaboos University, Muscat, Sultanate of Oman
3St. Thomas, Ontario, Canada
4Meteorite-Recovery Lab, Escondido, California, USA

We report precise triple oxygen isotope data of bulk materials and separated fractions of several Shergotty–Nakhla–Chassigny (SNC) meteorites using enhanced laser-assisted fluorination technique. This study shows that SNCs have remarkably identical Δ17O and a narrow range in δ18O values suggesting that these meteorites have assimilated negligibly small surface materials (<5%), which is undetectable in the oxygen isotope compositions reported here. Also, fractionation factors in coexisting silicate mineral pairs (px-ol and mask-ol) further demonstrate isotopic equilibrium at magmatic temperatures. We present a mass-dependent fractionation line for bulk materials with a slope of 0.526 ± 0.016 (1SE) comparable to the slope obtained in an earlier study (0.526 ± 0.013; Franchi et al. 1999). We also present a new Martian fractionation line for SNCs constructed from separated fractions (i.e., pyroxene, olivine, and maskelynite) with a slope of 0.532 ± 0.009 (1SE). The identical fractionation lines run above and parallel to our terrestrial fractionation line with Δ17O = 0.318 ± 0.016‰ (SD) for bulk materials and 0.316 ± 0.009‰ (SD) for separated fractions. The conformity in slopes and Δ17O between bulk materials and separated fractions confirm oxygen isotope homogeneity in the Martian mantle though recent studies suggest that the Martian lithosphere may potentially have multiple oxygen isotope reservoirs.

Reference
Ali A, Jabeen I, Gregory D, Verish R, Banerjee NR (2016) New triple oxygen isotope data of bulk and separated fractions from SNC meteorites: Evidence for mantle homogeneity of Mars. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12640]
Published by arrangement with John Wiley & Sons

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