Constraining iron content in the lower mantle through electrical conductivity of bridgmanite

Iron content in the lower mantle significantly influences mineral density and mantle convection dynamics. Electrical conductivity, an important physical property of minerals and rocks, is highly sensitive to iron content. Ground-based and satellite geomagnetic observations reveal radial and lateral variations in electrical conductivity in the lower mantle, where some conductive anomalies are up to one order of magnitude higher than the ambient mantle. However, the poorly understood quantitative correlation between iron content and electrical conductivity hinders our ability to decipher the composition of the lower mantle. We systematically measured the electrical conductivity of Al-bearing bridgmanite, the most abundant mineral in the lower mantle, as a function of iron content (X_Fe= 0.1–0.37) at 27 GPa and temperatures up to 2000 K, corresponding to conditions in the uppermost lower mantle. Our results demonstrate that bridgmanite conductivity increases substantially with iron content while exhibiting minimal temperature dependence. This remarkable sensitivity of bridgmanite conductivity to iron content enables us to constrain the iron content of the lower mantle through geomagnetic observations.