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The effect of pressure, temperature and composition on the distribution of Fe and Mg between olivine, orthopyroxene and liquid; an appraisal of the reversal in the normal fractionation trend in the Bushveld Complex

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Abstract

The coefficient for iron and magnesium exchange between olivine and liquid is modelled as a function of temperature in the simple system MgO-FeO-SiO2, and is found to be temperature insensitive in the range 1,200–1,400° C, but temperature sensitive at higher temperatures. In natural systems silica and the alkalis have a strong effect on the exchange coefficient. This effect is approximated by a simple mixture model for the silicate liquid.

The influence of pressure is theoretically estimated by the Clapeyron equation, and accord between predicted and observed values is found in experimental melts formed at 20 to 30 kbar. The equation for the exchange coefficient as a function of temperature, pressure and composition is used to test models for the reversal in the normal fractionation trend in the eastern and western Bushveld Complex. Multiple magma intrusion is the only satisfactory hypothesis for this feature.

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  1. Institute for Geological Research on the Bushveld Complex, University of Pretoria, Hillcrest, 0002, Pretoria, Republic of South Africa

    Christopher J. Hatton

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  1. Christopher J. Hatton
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Hatton, C.J. The effect of pressure, temperature and composition on the distribution of Fe and Mg between olivine, orthopyroxene and liquid; an appraisal of the reversal in the normal fractionation trend in the Bushveld Complex. Contr. Mineral. and Petrol. 86, 45–53 (1984). https://doi.org/10.1007/BF00373710

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  • DOI: https://doi.org/10.1007/BF00373710

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