Chemically homogeneous spin transition zone in Earthʹs lower mantle

The effect of spin crossover in lower mantle silicate perovskite (Pv) and ferropericlase (Fp) on the iron partitioning between these two phases remains uncertain, mainly due to the lack of in situ experiments under the relevant pressure and temperature conditions. By combining in situ synchrotron X-ray absorption and diffraction measurements on synthetic ringwoodite and natural (Mg0.88Fe0.12)2SiO4 San Carlos olivine at pressures between 22 GPa and 115 GPa treated at temperatures of 1950–2300 K, we found that temperature promotes iron partitioning into Pv, while pressure acts oppositely. There is only a limited effect of spin crossover in co-existing Pv and Fp on iron partitioning which cannot produce an appreciable chemical inhomogeneity within the Earthʹs lower mantle spin transition zone.