Numerical simulation of the graphite effect on the electrical conductivity of the upper mantle

Abstract

Summary The origin of high-conductivity anomalies in the deep earth is one of the hot issues in geosciences research. The presence of graphite is a possible reason, but the effects of the volume fraction and geometry of graphite on the high-conductivity anomaly in the upper mantle are still controversial. Based on the possible morphology of graphite in the uppermost mantle, graphite-olivine-orthopyroxene assemblage models are constructed, and their conductivities are calculated by a finite element method. The results show that when graphite is isolated from each other, temperature is the main factor that leads to a change in electrical conductivity. When graphite is in contact with each other, increases in the diameter/thickness ratio (β), orientation arrangement along the direction of conduction, and a mixture of powdered and disk-shaped graphite can significantly cause an increase in electrical conductivity. We found that a threshold value of graphite content exists, at which the model conductivity suddenly increases. The threshold decreases significantly with increasing β. A model with β larger than 25 could explain the high-conductivity anomaly in the upper mantle.