The oxidation state of europium as an indicator of oxygen fugacity

Abstract

The distribution of Eu between plagioclase feldspar and magmatic liquid has been determined experimentally for basaltic and andesitic systems as a function of temperature and oxygen fugacity at one atmosphere total pressure. Using the approach of Philpotts the ratios Eu 2+ Eu 3+ in plagioclase and coexisting magmatic liquid have been calculated. These ratios appear to be simply related to oxygen fugacity for the bulk compositions studied here. Using published trace element distribution data for natural rocks oxygen fugacities may be calculated from these experimental results. For terrestrial basalts calculated oxygen fugacities average 10 −7 with little dispersion from this value. Andesites average 10 −8.1 with considerable dispersion, while dacites and rhyodacites average 10 −9.1, also with considerable dispersion. Oxygen fugacities for lunar ferrobasalts cluster tightly around 10 −12.7. Data on achondritic meteorites are limited, but calculations indicate oxygen fugacities of two-to-five orders of magnitude lower than lunar ferrobasalts.