Upper mantle electrical conductivity in the Himalayan region

Abstract

The electrical conductivity profile of the Earth at depths of about 50 to 500 km was determined using the quiet ionospheric current variations observed at a line of stations near 75° East longitude. We found conductivity values of about 0.06 S/m from 50 to approximately 350 km depth with slight relative maxima near 125 and 275 kin, interpersed by relative minima near 210 and 330 km. Thereafter, the conductivity increased sharply toward a value of about 0.18 S/m at 500 km with no indication of leveling off. A comparison with regional seismic wave-velocity models shows good correspondence between high conductivity and low-velocity zones. The conduction by hydrogen-saturated pyroxene is envisaged as a possible mechanism for the high conductivity and its variation in the upper mantle.