Effect of temperature, pressure and chemical composition on the electrical conductivity of granulite and geophysical implications

Abstract

Electrical conductivities of three granulite samples (main minerals: plagioclase, quartz, and biotite) with different chemical compositions (W_B, the weight percent of Fe₂O₃ = 5.49, 8.75, and 14.79 wt%) were researched using a complex impedance spectroscopic technique at 1.0–3.0 GPa and 623–1073 K from 10⁻¹ to 10⁶ Hz. The experimental results indicated that the granulite conductivities markedly increased with temperature and slightly decreased with increasing pressure. Under the experimental conditions, the temperature dependence of the conductivities of granulite followed an Arrhenius relationship at certain temperatures. The electrical conductivities of granulite significantly increased with increasing biotite content and W_B. According to the activation enthalpies and previous studies, the conduction mechanism of the granulite samples with W_B = 8.75 and 14.79 wt% was small polaron conduction under the experimental conditions, and the conduction mechanisms of the granulite sample with W_B = 5.49 wt% were small polaron conduction at high temperatures and impurity conduction at low temperatures. The high conductivity anomalies under the ductile shear zones in southern India can be interpreted by the conductivities of granulite with interconnected biotite and a high iron content (>14.79 wt%).