Potassium isotopic compositions of enstatite meteorites

1,2Chen Zhao,1Katharina Lodders,1Hannah Bloom,1Heng Chen,1Zhen Tian,1Piers Koefoed,3Mária K. Pető,1Kun Wang (王昆)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13358]
1Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, Campus Box 1169, One Brookings Drive, St. Louis, Missouri, 63130 USA
2Faculty of Earth Sciences, China University of Geosciences, Wuhan, Hubei, 430074 China
3Konkoly Observatory, Research Center for Astronomy and Earth Sciences, Hungarian Academy of Sciences, H‐1121 Budapest, Hungary
Published by arrangement with John Wiley & Sons

Enstatite chondrites and aubrites are meteorites that show the closest similarities to the Earth in many isotope systems that undergo mass‐independent and mass‐dependent isotopic fractionations. Due to the analytical challenges to obtain high‐precision K isotopic compositions in the past, potential differences in K isotopic compositions between enstatite meteorites and the Earth remained uncertain. We report the first high‐precision K isotopic compositions of eight enstatite chondrites and four aubrites and find that there is a significant variation of K isotopic compositions among enstatite meteorites (from −2.34‰ to −0.18‰). However, K isotopic compositions of nearly all enstatite meteorites scatter around the bulk silicate earth (BSE) value. The average K isotopic composition of the eight enstatite chondrites (−0.47 ± 0.57‰) is indistinguishable from the BSE value (−0.48 ± 0.03‰), thus further corroborating the isotopic similarity between Earth’s building blocks and enstatite meteorite precursors. We found no correlation of K isotopic compositions with the chemical groups, petrological types, shock degrees, and terrestrial weathering conditions; however, the variation of K isotopes among enstatite meteorite can be attributed to the parent‐body processing. Our sample of the main‐group aubrite MIL 13004 is exceptional and has an extremely light K isotopic composition (δ41K = −2.34 ± 0.12‰). We attribute this unique K isotopic feature to the presence of abundant djerfisherite inclusions in our sample because this K‐bearing sulfide mineral is predicted to be enriched in 39K during equilibrium exchange with silicates.

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