Geochemical Evidence for Excess Iron in the Mantle Beneath Hawaii

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Science  01 Oct 2004:
Vol. 306, Issue 5693, pp. 91-94
DOI: 10.1126/science.1101050

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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.

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