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Science 25 January 2008:
Vol. 319. no. 5862, pp. 453 - 456
DOI: 10.1126/science.1149868
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Reports

Enriched Pt-Re-Os Isotope Systematics in Plume Lavas Explained by Metasomatic Sulfides

Ambre Luguet,1*{dagger} D. Graham Pearson,1 Geoff M. Nowell,1 Scott T. Dreher,1 Judith A. Coggon,1 Zdislav V. Spetsius,2 Stephen W. Parman1

To explain the elevated osmium isotope (186Os-187Os) signatures in oceanic basalts, the possibility of material flux from the metallic core into the crust has been invoked. This hypothesis conflicts with theoretical constraints on Earth's thermal and dynamic history. To test the veracity and uniqueness of elevated 186Os-187Os in tracing core-mantle exchange, we present highly siderophile element analyses of pyroxenites, eclogites plus their sulfides, and new 186Os/188Os measurements on pyroxenites and platinum-rich alloys. Modeling shows that involvement in the mantle source of either bulk pyroxenite or, more likely, metasomatic sulfides derived from either pyroxenite or peridotite melts can explain the 186Os-187Os signatures of oceanic basalts. This removes the requirement for core-mantle exchange and provides an effective mechanism for generating Os isotope diversity in basalt source regions.

1 Northern Centre for Isotopic and Elemental Tracing, Department of Earth Sciences, University of Durham, South Road, Durham DH1 3LE, UK.
2 Yakutian Research and Design Institute of Diamond Mining Industry, ALROSA Joint-Stock Company, Mirny, Yakutia 678170, Russia.

* Present address: Mineralogisch-Petrologisches Institut, Universität Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany.

{dagger} To whom correspondence should be addressed. E-mail: ambre.luguet{at}durham.ac.uk

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