Potassium Isotopic Compositions Of Enstatite Meteorites


Thin Section Photo of Sample MIL 13004 in Reflected Light with 5X Magnification

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 isotope 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 permil to -0.18 permil).

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 permil) is indistinguishable from the BSE value (-0.48 +/- 0.03 permil), thus further corroborating the isotopic similarity between Earth' 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 (delta 41K= -2.34 +/- 0.12 permil). 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.

Chen Zhao, Katharina Lodders, Hannah Bloom, Heng Chen, Zhen Tian, Piers Koefoed, Maria K. Peto, Kun Wang
(Submitted on 20 Feb 2020)

Comments: 46 pages, 7 figures, 2 tables, published in Meteoritics & Planetary Science
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
DOI: 10.1111/maps.13358
Cite as: arXiv:2002.08847 [astro-ph.EP] (or arXiv:2002.08847v1 [astro-ph.EP] for this version)
Submission history
From: Maria Pető
[v1] Thu, 20 Feb 2020 16:34:54 UTC (1,332 KB)
Astrobiology. Astrochemistry

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