Electrical Conductivity of Olivine, Wadsleyite, and Ringwoodite Under Upper-Mantle Conditions

• Published in: Science (American Association for the Advancement of Science) Vol. 280; no. 5368; pp. 1415 - 1418
• Main Authors: Xu, Yousheng, Poe, Brent T., Shankland, Thomas J., Rubie, David C.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for the Advancement of Science 29.05.1998; American Association for the Advancement of Science; The American Association for the Advancement of Science
• Subjects: Analysis; Climate; Conductivity; Crystalline rocks; Earth; Earth mantle; Earth sciences; Earth, ocean, space; Electric current; Electrical conductivity; Electrical resistivity; Electricity; Electrodes; Exact sciences and technology; Experimental petrology; Geology; Grade Point Average; High pressure; Laboratories; Mantle; Mantle (Geology); Mineralogy; Minerals; Minerals (Geology); Olivine; experimental studies; nesosilicates; two-layer models; upper mantle; seismic discontinuities; olivine; enthalpy; high pressure; ringwoodite; lateral variations; transition zones; instruments; activation energy; temperature; silicates; mantle; electrical conductivity
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.280.5368.1415

Geophysical models show that electrical conductivity in Earth's mantle rises about two orders of magnitude through the transition zone in the depth range 410 to 660 kilometers. Impedance measurements obtained on Mg$_1$ $_8$Fe$_0$ $_2$SiO$_4$ olivine, wadsleyite, and ringwoodite at up to 20 gigapascals and 1400°C show that the electrical conductivities of wadsleyite and ringwoodite are similar and are almost two orders of magnitude higher than that of olivine. A conductivity-depth profile to 660 kilometers, based on these laboratory data, shows a conductivity increase of almost two orders of magnitude across the 410-kilometer discontinuity; such a profile favors a two-layer model for the upper mantle. Activation enthalpies of 1.2 to 1.7 electron volts permit appreciable lateral variations of conductivity with lateral temperature variations.