MEASUREMENT OF ELECTRICAL CONDUCTIVITY OF GRANITE UNDER HIGH PRESSURE

Abstract

The electrical conductivity of dry granite has been studied at 300 to 1500°C and at 6 to 22 Kb by means of a piston cylinder type high pressure apparatus. Investigations have been made in both a non-powdered sample and a powdered sample in order to study intercrystalline effects. In a solid state, measurements were made in the three runs: the first heating run, the first cooling run and the second heating run. The activation energies for both samples at pressures up to about 10 Kb decreased in both the first cooling run and the second heating run compared with that in the first heating run, and at pressures more than 10 Kb, the conductivity curves in these three runs for the non-powdered sample agreed well with each other, while the proportionality constant for the powdered sample decreased by a factor of about 10 in both the first cooling run and the second heating run compared with that in the first heating run. Melting temperatures were determined from the discontinuous changes in the slope of the conductivity curve. The melting temperatures for dry granite increase with pressure and the melting intervals are about 200°C. The increase in the electrical conductivity for the dry granite at the time of melting is about 2 orders of magnitude at high pressures experienced. In a liquid state, not only the activation energy, E, but also the proprotionality constant, o_0, increase with pressure in such ways as aE/aP=4. 14X 10^-5eV/bar and a log o_0/aP= 1. 114 X 10^-4ohm^-1cm^-1/bar.