Determination of specific component activities in tholeiitic melts: principles and technique

Abstract
A method is presented for the determination of in situ FeO activities in polycomponent melts. The method utilizes the solubility of iron in platinum according to the equation: F e Pt + 1 2 O 2 = Fe O ( melt ) . . The activities of FeO in the melt have been determined by using the following expression. a FeO ( melt ) = p O 2 1 2 p O 2 0 1 2 a FeO 0 , where a FeO 0 is the activity of stoichiometric FeO in the particular iron oxide and p O 2 0 1 2 is the oxygen pressure in equilibrium with solid oxide and a Pt-Fe alloy containing the same amount of Fe as determined in the melt experiment. Attention is drawn to the possible errors which may be incurred by extrapolating values of a FeO from simple binary or ternary systems to multicomponent magmatic liquids, due to the presence of component interaction effects.

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