Anomalous compressibility of ferropericlase throughout the iron spin crossover

TL;DR

This study investigates the unusual elastic behavior of ferropericlase during the iron spin crossover at Earth's lower mantle conditions, revealing an anomalous bulk modulus reduction that impacts mantle dynamics.

Contribution

It provides first-principles insights into the thermoelastic anomalies of ferropericlase across the spin crossover under geophysical conditions.

Findings

Anomalous bulk modulus reduction during spin crossover.

The anomaly broadens with increasing temperature.

Potential implications for mantle viscosity and convection.

Abstract

The thermoelastic properties of ferropericlase Mg1-xFexO (x = 0.1875) throughout the iron high-to-low spin crossover have been investigated by first principles at Earth's lower mantle conditions. This crossover has important consequences for elasticity such as an anomalous bulk modulus (KS) reduction. At room temperature the anomaly is somewhat sharp in pressure but broadens with increasing temperature. Along a typical geotherm it occurs across most of the lower mantle with a more significant KS reduction around 1400-1600 km depth. This anomaly might also cause a reduction in the effective activation energy for viscous creep and lead to a viscosity minimum in the mid-lower mantle, in apparent agreement with results from inversion of data related with mantle convection and postglacial rebound.