An improved thermodynamic model of metal-olivine-pyroxene stability domains |
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| Authors: | J Matas Y Ricard L Lemelle F Guyot |
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| Institution: | (1) école normale supérieure de Lyon, UMR/CNRS F-5570, Lyon, France e-mail: jmatas@ens-lyon.fr; Fax: 1-510-643-9980, FR;(2) Laboratoire de Minéralogie-Cristallographie, Institut de Physique du Globe, Paris, France, FR |
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| Abstract: | Interactions between several silicate and metallic phases are studied by applying a self consistent thermodynamic approach
and using recent thermodynamic data. We compute proportions and compositions of oxidized silicates and of reduced metallic
phase in equilibrium at various temperatures and oxygen fugacities. The empirically observed activity-composition relationships
for ternary metallic alloys are used and their applications to a general thermodynamic expression for a non-regular ternary
system is explicitly discussed. We show that the stability limits of olivines and pyroxenes with respect to precipitation
of metallic phases under reducing conditions are directly related to the presence of nickel impurities. We precisely evaluate
the modifications of the stability limits as a function of nickel content. For typical mantle olivines Fe/(Fe+Mg) = 0.1]
the stability limits are given for values of x
Ni= Ni/(Ni+Fe+Mg) ranging from 10 ppm to 1% by: ln f
O2=−39.83+ 7.86 ln x
Ni, ln f
O2=−14.68+6.21 ln x
Ni, at 900 K and 1600 K, respectively.
Received: 17 November 1999 / Accepted: 14 May 2000 |
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