The electrical conductivity of upper-mantle rocks: water content in the upper mantle

The electrical conductivity of upper-mantle rocks-dunite, pyroxenite, and lherzolite-was measured at similar to 2-3 GPa and similar to 1,273 - 1,573 K using impedance spectra within a frequency range of 0.1-10(6) Hz. The oxygen fugacity was controlled by a Mo-MoO2 solid buffer. The results indicate that the electrical conductivity of lherzolite and pyroxenite are approximately half and one order of magnitude higher than that of dunite, respectively. A preliminary model involving water and iron content effects on the electrical conductivity was derived and is summarized by the relation: sigma = (105.2 +/- 0.4) C-W(0.67 +/- 0.07) exp ( - (183 +/- 9)kJ/mol)/RT) x exp (x (79 +/- 3)kJ/mol/RT) The results also indicate that pyroxenes dominate the bulk conductivity of upper mantle in hydrous conditions and suggest the maximum water content in oceanic upper mantle is as high as similar to 0.09 wt%.