Iron spin crossover in ferropericlase and its effect on lower-mantle thermal conductivity

TL;DR

This study measures the thermal conductivity of ferropericlase under lower-mantle conditions, revealing a significant decrease due to iron spin crossover, which impacts Earth's heat transfer and geodynamics.

Contribution

First direct measurements of ferropericlase's thermal conductivity at relevant mantle pressures and temperatures, highlighting the impact of iron spin crossover.

Findings

Conductivity decreases between 60 and 100 GPa at ~1700 K due to spin crossover.

Lower-mantle conductivity profile reaches ~10 W/m/K near the core-mantle boundary.

Results constrain mantle heat flux, plume buoyancy, and geodynamic evolution.

Abstract

Thermal conductivity of Earths lower mantle controls heat transfer across the core-mantle boundary (CMB) and strongly influences mantle convection. We report direct measurements of the thermal conductivity of single-crystal ferropericlase (Mg$_{1-x}$Fe$_x$O, $x = 0.09$-0.13), the second most abundant lower-mantle mineral, using optical laser flash and X-ray free-electron laser heating in diamond-anvil cells up to $\sim2200$~K and 130~GPa. These experiments provide the first conductivity data for ferropericlase at simultaneous lower-mantle pressures and temperatures. A marked reduction in conductivity between 60 and 100~GPa at $\sim1700$~K is consistent with the iron spin crossover. Combined with our previous results for Fe- and Fe,Al-bearing bridgmanite, the data define a lower-mantle conductivity profile that increases with pressure to $\sim10$~W\,m$^{-1}$\,K$^{-1}$ near the CMB, constraining mantle heat flux, plume buoyancy, and long-term geodynamic evolution.