Partial‐melt electrical conductivity: Influence of melt composition

<jats:p>The electrical conductivity of a partial melt is influenced by many factors, including melt conductivity, crystalline conductivity, and melt fraction, each of which is influenced by temperature. We have performed measurements of bulk conductivity as a function of temperature of an Fo<jats:sub>80</jats:sub>‐basalt partial melt between 684° and 1244°C at controlled oxygen fugacity. Melt fraction and composition variations with temperature calculated using MELTS [Ghiorso and Sack, 1995] indicate that the effect on melt conductivity of changing melt composition is balanced by changes in temperature (T). Thus bulk conductivity as a function of T or melt fraction in this system can be calculated assuming a constant melt conductivity. The bulk conductivity is well modeled by simple parallel calculations, by the Hashin‐Shtrikman upper bound, or by Archie's law (σ<jats:sub>partial</jats:sub> <jats:sub>melt</jats:sub>/σ<jats:sub>melt</jats:sub> = <jats:italic>C</jats:italic><jats:sub>1</jats:sub>X<jats:sub><jats:italic>m</jats:italic></jats:sub><jats:sup>n</jats:sup>). We estimate apparent values of the Archie's law parameters between 1150° and 1244°C as <jats:italic>C</jats:italic><jats:sub>1</jats:sub> = 0.73 ± 0.02 and <jats:italic>n</jats:italic> = 0.98 ±0.01. Estimates of the permeability of the system are obtained by using an electrical conductivity‐critical scale length relationship and range from ∼10<jats:sup>−14</jats:sup> to 10<jats:sup>−18</jats:sup> m<jats:sup>2</jats:sup>, comparing favorably with previously published values.</jats:p>