title: Solid-liquid density and spin crossovers in (Mg, Fe)O system at deep mantle conditions.
abstract: The low/ultralow-velocity zones in the Earth's mantle can be explained by the presence of partial melting, critically depending on density contrast between the melt and surrounding solid mantle. Here, first-principles molecular dynamics simulations of (Mg, Fe) O ferropericlase in the solid and liquid states show that their densities increasingly approach each other as pressure increases. The isochemical density difference between them diminishes from 0.78 (±0.7) g/cm3at zero pressure (3000 K) to 0.16 (±0.04) g/cm3at 135 GPa (4000 K) for pure and alloyed compositions containing up to 25% iron. The simulations also predict a high-spin to low-spin transition of iron in the liquid ferropericlase gradually occurring over a pressure interval centered at 55 GPa (4000 K) accompanied by a density increase of 0.14 (±0.02) g/cm3. Temperature tends to widen the transition to higher pressure. The estimated iron partition coefficient between the solid and liquid ferropericlase varies from 0.3 to 0.6 over the pressure range of 23 to 135 GPa. Based on these results, an excess of as low as 5% iron dissolved in the liquid could cause the solid-liquid density crossover at conditions of the lowermost mantle.
authors.affiliation: School of Electrical Engineering and Computer Science, Louisiana State University, Baton Rouge, LA 70803.
authors.forename: Dipta B
authors.initials: DB
authors.lastname: Ghosh
authors.affiliation: School of Electrical Engineering and Computer Science, Louisiana State University, Baton Rouge, LA 70803.|Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803.|Center for Computation and Technology, Louisiana State University, Baton Rouge, LA 70803.
authors.forename: Bijaya B
authors.initials: BB
authors.lastname: Karki