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Two oxygen isotopic components with extra-selenial origins observed among lunar metallic grains – In search for the solar wind component

Ko Hashizume & Marc Chaussidon Geochimica et Cosmochimica Acta, 2009, vol. 73, pp.3038-3054

doi:10.1016/j.gca.2009.02.024

Two oxygen isotopic components with extra-selenial origins observed among lunar metallic grains – In search for the solar wind component Purchase the full-text article

Geochimica et Cosmochimica Acta Article in Press

Ko Hashizume a and Marc Chaussidon b

aDepartment of Earth & Space Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan

bCRPG-Nancy Université-CNRS, BP 20, 54501 Vandoeuvre-lès-Nancy Cedex, France

Received 15 September 2008 ; accepted 20 February 2009. Associate editor : Rainer Wieler. Available online 4 March 2009.

Abstract

Oxygen isotopic analyses were performed in the surface layers of lunar metallic grains from lunar regolith samples 71501 and 79035, presumably exposed at the Moon surface at different times. We were able to reproduce the two extreme O components previously found [Hashizume K. and Chaussidon M. (2005) A non-terrestrial 16O-rich isotopic composition for the protosolar nebula. Nature 434, 619–622 ; Ireland T. R., Holden P., Norman M. D. and Clarke J. (2006) Isotopic enhancements of 17O and 18O from solar wind particles in the lunar regolith. Nature 440, 776–778], with a range observed of −12 ± 5 < Δ17O < +33 ± 3‰ (1σ). The relatively minor 16O-rich component corresponding to an end-member Δ17O value lower than −20‰ is likely the solar component. This comes from the fact that its concentration roughly agrees with the maximum solar wind abundance expected among the grains from the two samples. At variance the 16O-poor component is 5–10 times more abundant and thus likely non-solar. The δ18O range found for the 16O-poor component may reflect various processes such as isotope exchange reaction during oxidation of metallic iron and/or isotope fractionation by evaporation/condensation at the surface of the Moon or during implantation at depth in the lunar metallic grains. The present study suggests that planetary solid materials in bulk are systematically depleted in 16O relative to the solar isotopic composition, suggesting the existence of non-mass-dependent isotopic fractionations associated to the formation of solids in the accretion disk.

Voir en ligne : doi:10.1016/j.gca.2009.02.024




publié jeudi 2 avril 2009