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Lithium isotope evidence for subduction-enriched mantle in the source of mid-ocean-ridge basalts

Nature volume 443, pages 565568 (05 October 2006) | Download Citation

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Abstract

‘Recycled’ crustal materials, returned from the Earth's surface to the mantle by subduction, have long been invoked to explain compositional heterogeneity in the upper mantle1. Yet increasingly, problems have been noted with this model2,3. The debate can be definitively addressed using stable isotope ratios, which should only significantly vary in primitive, mantle-derived materials as a consequence of recycling. Here we present data showing a notable range in lithium isotope ratios in basalts from the East Pacific Rise, which correlate with traditional indices of mantle heterogeneity (for example, 143Nd/144Nd ratios). Such co-variations of stable and radiogenic isotopes in melts from a normal ridge segment provide critical evidence for the importance of recycled material in generating chemical heterogeneity in the upper mantle. Contrary to many models, however, the elevated lithium isotope ratios of the ‘enriched’ East Pacific Rise lavas imply that subducted ocean crust is not the agent of enrichment. Instead, we suggest that fluid-modified mantle, which is enriched during residency in a subduction zone, is mixed back into the upper mantle to cause compositional variability.

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Acknowledgements

Analytical work was supported by a Philip Leverhulme Prize awarded to T.E. A.J. was supported by an NERC studentship. Reviews by B. Leeman were appreciated. We also thank J. Blundy, C. Hawkesworth and D. Vance for comments on versions of the mansucript.

Author information

Author notes

    • Alistair Jeffcoate

    †Present address: Rio Tinto Iron Ore Atlantic, PO Box 695, 8th Floor, Castlemead, Lower Castle Street, Bristol BS99 1FS, UK

Affiliations

  1. Bristol Isotope Group, Department of Earth Sciences, Wills Memorial Building, Queen's Road, University of Bristol, Bristol BS8 1RJ, UK

    • Tim Elliott
    • , Alex Thomas
    •  & Alistair Jeffcoate
  2. Department of Earth Sciences, South Parks Road, Oxford University, Oxford OX1 3PR, UK

    • Alex Thomas
  3. Department of Earth Sciences, Durham University, Durham DH1 3LE, UK

    • Yaoling Niu

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Competing interests

Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.

Corresponding author

Correspondence to Tim Elliott.

Supplementary information

Word documents

  1. 1.

    Supplementary Table 1

    Table of all EPR MORB Li isotope data

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https://doi.org/10.1038/nature05144

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