Electrical conductivity anisotropy of natural deformed talc rocks and serpentinite at 3 GPa

The electrical conductivity anisotropy of deformed natural talc rocks and serpentinite was investigated using an impedance analyzer in the frequency range 10-3-106 Hz along three directions: the direction parallel to lineation of oriented minerals (X direction), the direction perpendicular to lineation on the foliation plane (Y direction), and the direction perpendicular to the foliation (Z direction) at 3 GPa. The temperature ranges for the conductivity measurements were 500-1000 K for talc rock, and 500- 900K for serpentinite. The talc rock is composed of talc and the serpentinite is mainly composed of antigorite and a small amount of tremolite and ilmenite opaque mineral. For both rocks, the electrical conductivities parallel to the X direction and the Z direction are the highest and the lowest, respectively. The electrical conductivity anisotropy for the talc rocks is stronger than that for the serpentinite. Electrical conductivities of the serpentinite are higher than the talc rock. The electrical conductivities of talc and serpentinite sample with higher water content (>7 wt.%) are similar with hydrous olivine single crystal (water content about 177 ppm). The electrical conductivity increases in orders of talc, serpentine and brucite, indicating the dependence of the electrical conductivity on water content. The activation enthalpy of talc rock is the lowest (0.59 eV) in the X direction and the highest (0.68 eV) in the Z direction. The activation enthalpies of the serpentinite in different directions show the consistent value, 0.74 eV, for the experiments using Mo electrodes. In the case of using Ni electrodes, the activation enthalpies are 0.70 eV, 0.66 eV and 0.68 eV for the measurements in X, Y and Z direction respectively. The higher electrical conductivity and the lower activation enthalpy of the serpentine using Ni-NiO buffer are attributed to the higher fO2 of Ni-NiO buffer. The electrical conductivity anisotropy strongly depends on the crystal structure and orientation of minerals during deformation. Furthermore, grain interior conductivity, grain boundary conductivity (σgb) and electrode reaction can be recognized from the impedance arcs. Relationship between logσgb and reciprocal temperature shows the linear relationship as well as the grain interior conductivity. The total electrical conductivities are reduced by the grain boundary conductivities.