Effect of Pressure on the Composition of the Lower Mantle End Member FexO

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Science  01 Jan 1993:
Vol. 259, Issue 5091, pp. 66-68
DOI: 10.1126/science.259.5091.66


The composition limits of FexO are sensitive to both pressure and temperature. Earlier studies have shown that FexO becomes highly nonstoichiometric when in equilibrium with metallic iron above 10 gigapascals, which is difficult to reconcile with available thermodynamic data. Experiments with a uniaxial split-sphere apparatus demonstrate that the iron content of FexO increases continuously at high pressure in excellent agreement with quantitative models and suggest that there is a discontinuity in the elastic properties of FexO above x = 0.95. On the basis of these results, it is inferred that the Earth's present lower mantle is not in equilibrium with metallic iron.