Electrical conductivity of olivine at high pressure and under controlled oxygen fugacity

Electrical conductivity σ in the [100] direction has been determined for the Red Sea olivine (Fo 91) to 1440°C and 8 kbar in argon. No systematic variation of σ with pressure was observed. The effect of an 8-kbar variation in pressure over the 1270°–1440°C range is equivalent to a temperature uncertainty of ±5°C. We have also determined σ on the same sample up to 1660°C with controlled oxygen fugacity ƒo2 at 1 bar of total pressure. By using published σ-depth profiles and assuming olivine as the major phase in the earth's upper mantle with ƒ o 2 = 10 −6 -10 −3 bar, temperatures of the upper mantle are calculated as a function of depth. The temperature uncertainty due to possible pressure effects is 2–5 times smaller than that resulting from the ambiguity in published σ-depth profiles.