Electrical conductivity of epidote with a low dehydration rate and its geophysical implications Available to Purchase

The dehydration of hydrous minerals in subduction zones is a crucial factor affecting water circulation and altering physical properties at depth. High-conductivity anomalies observed in magnetotelluric studies have been commonly attributed to the release of fluids from hydrous minerals. However, the coupling between the variations in electrical conductivity and dehydration kinetics remains unclear. We measured the electrical conductivity of epidote under the conditions of 0.5−3.0 GPa and 573−1473 K. Notably, at ∼300 K above the stability threshold of epidote, conductivity increased moderately, and the activation energy was 35−124 kJ/mol. Additionally, epidote exhibited an extremely slow dehydration rate at temperatures lower than 1273 K. At 1373−1473 K, the conductivity increased rapidly to ∼2 S/m, and the activation energy significantly increased to 115−393 kJ/mol. Our results suggest that the slow increase in the conductivity was due to the ultra-slow dehydration of epidote, while the rapid increase in the conductivity was due to the complete decomposition of epidote into garnet, anorthite, iron oxides, quartz, and water. Based on our geothermal gradient and geophysical observations, we propose that the ultra-slow dehydration of epidote may be a cause of the continuously high conductivity observed at depths of 100−220 km in cold subduction zones.