Effect of Temperature, Pressure, and Chemical Composition on the Electrical Conductivity of Schist: Implications for Electrical Structures under the Tibetan Plateau.

The experimental study on the electrical conductivities of schists with various contents of alkali ions (C(A) = K₂O + Na₂O = 3.94, 5.17, and 5.78 wt.%) were performed at high temperatures (623⁻1073 K) and high pressures (0.5⁻2.5 GPa). Experimental results indicated that the conductivities of schist markedly increased with the rise of temperature. Pressure influence on the conductivities of schist was extremely weak at the entire range of experimental temperatures. Alkali ion content has a significant influence on the conductivities of the schist samples in a lower temperature range (623⁻773 K), and the influence gradually decreases with increasing temperature in a higher temperature range (823⁻1073 K). In addition, the activation enthalpies for the conductivities of three schist samples were fitted as being 44.16⁻61.44 kJ/mol. Based on the activation enthalpies and previous studies, impurity alkaline ions (K⁺ and Na⁺) were proposed as the charge carriers of schist. Furthermore, electrical conductivities of schist (10(-3.5)⁻10(-1.5) S/m) were lower than those of high-conductivity layers under the Tibetan Plateau (10(-1)⁻10⁰ S/m). It was implied that the presence of schist cannot cause the high-conductivity anomalies in the middle to lower crust beneath the Tibetan Plateau.