EPSS Colloquium winter-2020

To further our understanding of the communication between the deep Earth and its surface and atmosphere, we explore how redox state affects mantle mineralogy, density, seismic velocities and melting and in turn what this could mean for convection and thermochemical evolution of the planet. Mantle ferric iron Fe3+content and its distribution are largely unconstrained and are influenced by the disproportionation of Fe2+ through the formation of Earth’s most abundant mineral bridgmanite, and the presence of other minor elements such as aluminum and water. Here we show that redox-induced density contrast (~1-2%) affects mantle convection and may potentially cause the oxidation of the upper mantle. Our geodynamic simulations suggest that such a density contrast causes a rapid ascent and accumulation of oxidized material in the upper mantle, with descent of the denser, reduced material to the core–mantle boundary. The resulting heterogeneous redox conditions in Earth’s interior may have contributed to the large low-shear velocity provinces in the lower mantle and the rise of oxygen in Earth’s atmosphere. Using a combination of laser-heated diamond anvil cell experiments, Monte Carlo simulations, geodynamic modeling, and seismic forward modeling calculations, our work shows the importance of ferric iron content and its effects on overall rock mineralogy in the lower mantle. Therefore, geophysical anomalies in the mantle may reflect not only differences in bulk composition or temperature, but also mantle oxidation state.