Wenqing Sun

Influence of anisotropy on the electrical conductivity and diffusion coefficient of dry K-feldspar: Implications of the mechanism of conduction

The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K-1223 K and 1.0 GPa-3.0 GPa in a frequency range of 10(-1) Hz-10(6) Hz. The measured electrical conductivity along the perpendicular to [001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 +/- 0.06 eV and 2.51 +/- 0.19 cm(3)/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the perpendicular to[001] axis is approximately three times higher than that along the perpendicular to [100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst-Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.

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

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.