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Science 19 April 2002:
Vol. 296. no. 5567, pp. 516 - 518
DOI: 10.1126/science.1069119
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Reports

Evidence for an Ancient Osmium Isotopic Reservoir in Earth

Anders Meibom,1* Robert Frei2

Iridosmine grains from placer deposits associated with peridotite-bearing ophiolites in the Klamath mountains have extremely radiogenic 186Os/188Os ratios and old Re-Os minimum ages, from 256 to 2644 million years. This indicates the existence of an ancient platinum group element reservoir with a supra-chondritic Pt/Os ratio. Such a ratio may be produced in the outer core as a result of inner core crystallization that fractionates Os from Pt. However, if the iridosmine Os isotopic compositions are a signature of the outer core, then the inner core must have formed very early, within several hundred million years after the accretion of Earth.

1 Geological and Environmental Sciences, 320 Lomita Mall, Stanford University, CA 94305-2115, USA.
2 Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen, Denmark.
*   To whom correspondence should be addressed. E-mail: meibom{at}pangea.stanford.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Temporal Evolution of the Lithospheric Mantle beneath the Eastern North China Craton.
Z.-Y. Chu, F.-Y. Wu, R. J. Walker, R. L. Rudnick, L. Pitcher, I. S. Puchtel, Y.-H. Yang, and S. A. Wilde (2009)
J. Petrology 50, 1857-1898
   Abstract »    Full Text »    PDF »
On the formation of peridotite-derived Os-rich PGE alloys.
F. E. Brenker, F. E. Brenker, A. Meibom, and R. Frei (2003)
American Mineralogist 88, 1731-1740
   Abstract »    Full Text »    PDF »


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