Pressure-temperature range of reactions between liquid iron in the outer core and mantle silicates
The possibility of reaction between the liquid iron of the Earth's outer core and crystalline silicates ((Mg, Fe)SiO_3) of the mantle, Mg_(0.9), Fe_(0.1)SiO_3(pv) + 0.15 Fe (ϵ) = 0.9MgSiO_3 (pv) + 0.2FeO (hpp) + 0.05 FeSi (ϵ) + 0.05 SiO_2 (st), was proposed by Knittle and Jeanloz (1989,1991) on the basis of exploratory experiments. We calculate Gibbs free-energies for the reactants and the products of the above reaction in order to constrain the pressure-temperature range. Upon application of thermal expansion, equation of state and heat capacity data, we demonstrate that this reaction can occur at pressures as low as 30 GPa at 3500 K, and at temperatures as low as 900 K at the 130 GPa pressure of the present core-mantle boundary. Furthermore, we propose a modified equation of reaction at the core-mantle boundary: Mg_(0.9)Fe_(0.1)SiO_3 (pv) + 0.3Fe (ϵ) = 0.9MgSiO_3 (pv) + 0.3FeO(hpp) + 0.1FeSi. Our results imply that similar reactions may occur during the early accretion history of the Earth.
© 1994 by the American Geophysical Union. Paper number 93GL03262. Received September 10, 1993; accepted November 11, 1993. We thank Don L. Anderson, Joel Ita and John Beckett for their comments and suggestions. Research supported by National Science Foundation. Division of Geological and Planetary Sciences, California Institute of Technology, Contribution 5324.
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