Orientation-related electrical conductivity of hydrous olivine, clinopyroxene and plagioclase and implications for the structure of the lower continental crust and uppermost mantle

Orientation-related electrical conductivity of H-annealed olivine, clinopyroxene and plagioclase single crystals have been measured at 10 kbar and 200–800 °C with an end-loaded piston cylinder apparatus and a Solartron-1260 Impedance/Gain Phase analyzer in the frequency range of 106–0.1 Hz. The complex spectra usually show an arc over the whole frequency range at low temperature, with much scatter of data-points at low frequencies for samples of large resistance, and an arc plus a short tail in the high and low frequency range, respectively, at high temperature. The arc is due to grain interior conduction, and the short tail is related to electrode effects. The conduction is dominated by H-related point defects. The results show negligible anisotropy in electrical conductivity for hydrous olivine and clinopyroxene but large anisotropy for hydrous plagioclase. Electrical anisotropy in the lower continental crust may be caused by the fabrics of the constitutive granulites due to lattice-preferred orientation (LPO) of hydrous plagioclase and banded pyroxene- and plagioclase-rich microstructure. Electrical anisotropy in the uppermost mantle cannot be produced by hydrous olivine (and pyroxenes in peridotites), but may be related to mantle macro-heterogeneity due to the local presence of Fe3 +- and H2O-rich augites and other pyroxenites in the form of dykes/veins and/or remnants of recycled crustal materials in the form of stretched lenses.