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The origin of aubrites: Evidence from lithophile trace element abundances and oxygen isotope compositions

Barrat, J.A.; Greenwood, R.C.; Keil, K.; Rouget, M.L.; Boesenberg, J.S.; Zanda, B. and Franchi, I.A. (2016). The origin of aubrites: Evidence from lithophile trace element abundances and oxygen isotope compositions. Geochimica et Cosmochimica Acta, 192 pp. 29–48.

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We report the abundances of a selected set of “lithophile” trace elements (including lanthanides, actinides and high field strength elements) and high-precision oxygen isotope analyses of a comprehensive suite of aubrites. Two distinct groups of aubrites can be distinguished: (a) the main-group aubrites display flat or light-REE depleted REE patterns with variable Eu and Y anomalies; their pyroxenes are light-REE depleted and show marked negative Eu anomalies; (b) the Mount Egerton enstatites and the silicate fraction from Larned display distinctive light-REE enrichments, and high Th/Sm ratios; Mount Egerton pyroxenes have much less pronounced negative Eu anomalies than pyroxenes from the main-group aubrites.

Leaching experiments were undertaken to investigate the contribution of sulfides to the whole rock budget of the main-group aubrites. Sulfides contain in most cases at least 50% of the REEs and of the actinides. Among the elements we have analyzed, those displaying the strongest lithophile behaviors are Rb, Ba, Sr and Sc.

The homogeneity of the Δ17O values obtained for main-group aubrite falls [Δ17O = +0.009 ± 0.010‰ (2σ)] suggests that they originated from a single parent body whose differentiation involved an early phase of large-scale melting that may have led to the development of a magma ocean. This interpretation is at first glance in agreement with the limited variability of the shapes of the REE patterns of these aubrites. However, the trace element concentrations of their phases cannot be used to discuss this hypothesis, because their igneous trace-element signatures have been modified by subsolidus exchange. Finally, despite similar O isotopic compositions, the marked light-REE enrichments displayed by Mount Egerton and Larned suggest that they are unrelated to the main-group aubrites and probably originated from a distinct parent body.

Item Type: Journal Item
Copyright Holders: 2016 Elsevier Ltd
ISSN: 0016-7037
Keywords: aubrite; trace elements; oxygen isotopes; Oldhamite
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 48197
Depositing User: Richard Greenwood
Date Deposited: 16 Jan 2017 14:15
Last Modified: 11 Jun 2020 15:29
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