The electrical conductivity of lherzolite

Journal Article · Sat Jul 10 04:00:00 EDT 1993 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/93JB00995· OSTI ID:83353

Duba, A ^[1]; Constable, S ^[2]

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1. Lawrence Livermore National Lab., CA (United States)
2. Scripps Institution of Oceanography, La Jolla, CA (United States)

Electrical conductivity as a function of oxygen fugacity (f{sub O2}) between 10{sup {minus}5} Pa and 1 Pa, temperature between 700{degrees}C and 1200{degrees}C, and time over a period of 1700 hours are reported for a lherzolite nodule from Mount Porndon, Australia. Analysis of complex impedance collected at 100 Hz, 1 kHz, and 10 kHz indicates that there is significant frequency dispersion in this rock at temperatures below 900{degrees}C-1000{degrees}C. By choosing the resistance of an equivalent parallel RC network at the frequency having minimum phase, the effect of dispersion is largely avoided. Conductivity as a function of time, collected following changes in f{sub O2} at 1010 and 1200{degrees}C, has been analyzed to determine the diffusivity of defects relating f{sub O2} to the electrical conduction mechanism in olivine. The diffusivities so obtained are in remarkably good agreement with those determined from strain measurements during creep tests, which implies that magnetism vacancies are the rate-limiting step for conductivity reequilibration after f{sub O2} changes. A longer-term process is observed in this rock in which the conductivity drifts upward or downward with a time constant of hundreds of hours after initial reequilibration to gas mix (f{sub O2}) changes. The authors speculate that this long-term drift could be related to equilibration of the iron distribution between coexisting olivine and pyroxene as a function of f{sub O2}. The lherzolite conductivity data are not significantly different from measurements made on olivine single crystals and polycrystals, even though the rock contains about 34 model % pyroxene. This consistency of laboratory measurements of electrical conductivity of olivines from many localities and geological settings supports the use of recent models relating mantle temperature with electrical conductivity in the interpretation of mantle geo/electromagnetic soundings. 33 refs., 11 figs., 3 tabs.

• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 83353
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: B7 Vol. 98; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
EARTH MANTLE
ELECTRIC CONDUCTIVITY
OLIVINE
OXYGEN
PYROXENES
ROCKS