Electrical conductivity of tremolite under high temperature and pressure: implications for the high-conductivity anomalies in the Earth and Venus

We measured the electrical conductivity of tremolite over a range of pressures (1.0, 1.5, and 2.0 GPa) and temperatures (648–1373 K). At temperatures lower than 1173 K, the electrical conductivity of tremolite was ~ 0.001 S/m, but once the dehydroxylation reaction took place at 1173 K, we observed a significant increase in the electrical conductivity. The electrical conductivity continued to increase until it reached its maximum value of ~ 1 S/m at a temperature of 1373 K, which we attributed to dehydroxylation in the tremolite samples. The electrical behavior was altered by the physical breakdown of the tremolite structure, rather than the oxidation process. The decomposition of tremolite resulted in the creation of diopside, enstatite, and quartz. To explain some anomalous conductivity measurements, we propose that iron-free amphibole experiences a dehydroxylation mechanism that differs from the dehydroxylation mechanism observed in iron-bearing amphiboles. Our conductivity analyses indicate that the observed increase in the electrical conductivity in deep subduction regions (at depths of ~ 180 km) is driven by the dehydroxylation of tremolite and by the mixing of lherzolite and tremolite in the upper mantle. Using our data and previously published temperature gradient data, we were able to extrapolate reasonable electrical conductivity values for the surface and interior of Venus.