Abstract
The loss of iron from starting compositions to noble-metal capsule materials is a serious experimental problem which occurs at high temperature over the most interesting ranges of oxygen fugacity. One-atmosphere experiments indicate that equimolar substitution of CoO for FeO creates an analogue system which maintains constant composition, enabling equilibrium experiments to be performed. Using CoO as a chemical substitute for FeO permits the experimenter to simulate any desired oxygen fugacity, accurately reproduce phase relations occurring in ferromagnesian systems, and generate liquid compositions which may be corrected to yield accurate estimations of FeO-bearing liquids. To a lesser degree, temperatures may also be corrected. Available data indicate that the analogue remains valid at high pressure. Thus, the cobalt analogue technique provides a flexible alternative for modelling mafic systems at high temperature while avoiding the ‘iron-loss problem.’
