The effect of composition on the ferric-ferrous ratio in basaltic liquids at atmospheric pressure

The effects on the ferric-ferrous ratio of varying individual components in a dry basaltic liquid have been determined at atmospheric pressure and constant oxygen fugacity (fO₂). Experiments were conducted by suspending 100 mg samples from pt loops at 1200°C (fO₂ = 10^?8atm) and 1360°C (fO₂ = 10^?6atm) in an atmosphere controlled by mixtures of CO₂ and H₂. A microanalytical wetchemical technique and the electron microprobe were used to determine the composition of the resulting basaltic glasses. In order of decreasing significance, the addition of oxides of K, Na, Si, Al, or Ca produces an increase in the ferric-ferrous ratio of the melt at 1200°C. The change in the ferric-ferrous ratio produced by component addition is less at 1360°C than at 1200°C.