Abstract
An equilibrium assemblage of olivine, Ca-free pyroxene, and PtFe alloy can be used to calculate oxygen fugacity at a known temperature and pressure. This oxygen geobarometer has been tested T = 1300-1450°C, P = 1 bar and 10 kbar. The calculated log may be compared with that determined by the mixture used to control the furnace atmosphere in the 1 bar experiments and, in the case of the 10 kbar experiments, the log determined from the graphite-fluid equilibrium. The average deviation of the calculated log and that determined by other means is 0.2; the maximum absolute difference is 0.4. The distribution coefficient () for Fe and Mg between coexisting olivine and pyroxene was found to range from 1.14 at to , and varies systematically with the Fe/(Fe + Mg) of the phases.
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