Electronic spin transition of iron in the Earth’s lower mantle

Abstract

Silicate perovskite and ferropericlase are thought to be the primary constituents of the lower mantle, whereas silicate post-perovskite is more likely found in the lowermost mantle. Because these minerals contain certain amounts of iron, their properties and, consequently, those of the deep mantle, are strongly influenced by iron’s spin and valence states. A high-spin to low-spin crossover in ferropericlase has been observed to occur in the middle part of the lower-mantle conditions. Recent Mossbauer results consistently show that Fe2 + predominantly exhibits extremely high quadrupole splittings in perovskite and post-perovskite, whereas a high-spin to low-spin transition of Fe3 + in the octahedral site occurs at high pressures. These results provide a new venue for discussion of the effects of the spin and valence states of iron on the physical and chemical properties of the lower mantle.