Electrical Conductivity of Talc Dehydration at High Pressures and Temperatures: Implications for High‐Conductivity Anomalies in Subduction Zones

Abstract

AbstractThe dehydration of hydrous minerals is one of the causes of high‐conductivity anomalies in subduction zones. To determine the origin of these anomalies, the trade‐off between the dehydration and conduction mechanisms of hydrous minerals at high pressures and temperatures should be clarified. Talc is a typical hydrous mineral in hot subduction zones, and previous studies may have underestimated its contribution to high‐conductivity anomalies. We report the new electrical conductivity results for talc, which were measured at 1.0–4.0 GPa and 523–1293 K using impedance spectroscopy. The pressure effect on conductivity of talc is obvious in the different heating stages. The pressure decreased the conductivity prior to dehydration and remarkably increased the conductivity during dehydration. A sharp conductivity increase was observed beyond the dehydration temperature, and the maximum conductivity was 0.1 S/m. The increase in conductivity associated with a high activation energy of 284.5 ± 11.8 kJ/mol and an activation volume of −6.2 ± 0.6 cm3/mol was attributed to an inhomogeneous dehydration model involving cation migration. The talc dehydration temperatures at different pressures derived from the conductivity inflection points are 1023–1093 K. The increased electrical conductivity produced by talc ongoing dehydration provides an explanation for the high‐conductivity anomalies observed at deep depths in hot subduction zone. The silica‐rich fluid released by talc may contribute to the silica deposition in plate interface and induce the high‐conductivity anomalies observed at shallow depths in the hot subduction zones.