The Influence of Dehydration on the Electrical Conductivity of Trachyandesite at High Temperatures and High Pressures

Abstract

The electrical conductivity of trachyteandesite was measured in situ under conditions of pressure range from 0.5-2.0 GPa and temperature range from 773-1,323 K using a YJ-3000t multi-anvil press and a Solartron-1260 Impedance/Gain-phase Analyzer. The experimental results indicate that the electrical conductivity of trachyteandesite increases with increasing temperature and decreases with a rise in pressure. The relationship between the electrical conductivity (σ) and temperature (T) conforms to the Arrhenius equation within a certain temperature range. When the temperature rises to 923 K, the electrical conductivity of trachyandesite abruptly increases. This result demonstrates that trachyandesite begins to dehydrate at ~923 K and produces magnetite with a high-conductivity mineral phase after dehydration. The intergrowth of interconnected magnetite is the cause for the ~2 orders of magnitude increase in the electrical conductivity after dehydration. The interconnected high-conductivity mineral phase of magnetite in the dehydration product of the trachyandesite sample can be used to reasonably explain the high-conductivity anomalies in the South-Central Chilean subduction zone beneath the Andes.