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Science 1 October 2004:
Vol. 306. no. 5693, pp. 91 - 94
DOI: 10.1126/science.1101050
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Reports

Geochemical Evidence for Excess Iron in the Mantle Beneath Hawaii

Munir Humayun,1,2* Liping Qin,1 Marc D. Norman3

Chemical interaction of Earth's mantle with the liquid outer core should influence the mantle's iron content. Osmium isotope ratios in Hawaiian lavas indicate a mass flux of ≤1% core to the mantle, which is the immediate source of these lavas. We present precise measurements of the Fe/Mn ratio for Hawaiian lavas, revealing an increase of 1 to 2% in the mole fraction of iron in the mantle beneath Hawaii. This corresponds to a density anomaly of about 0.5%, about the same magnitude observed in seismic tomography models of the Pacific superswell region. These data also rule out a role for Mn-rich sediments as the source of the Hawaiian Os isotope signal.

1 Department of the Geophysical Sciences, 5734 South Ellis Avenue, Chicago, IL 60637, USA.
2 National High Magnetic Field Laboratory and Department of Geological Sciences, Florida State University, Tallahassee, FL 32310, USA.
3 Research School of Earth Sciences, Australian National University, Canberra ACT 0200, Australia.

* To whom correspondence should be addressed. E-mail: humayun{at}magnet.fsu.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)