Influence of the iron spin crossover in ferropericlase on the lower mantle geotherm

Abstract

The iron spin crossover in ferropericlase introduces anomalies in its thermodynamics and thermoelastic properties. Here we investigate how these anomalies can affect the lower mantle geotherm. The effect is examined in mantle aggregates consisting of mixtures of bridgmanite, ferropericlase, and CaSiO${}_3$ perovskite, with different Mg/Si ratios varying from harzburgitic to perovskitic (Mg/Si$\sim$1.5 to 0.8). We find that the anomalies introduced by the spin crossover increase the isentropic gradient and thus the geotherm proportionally to the amount of ferropericlase. The geotherms can be as much as $\sim$ 200K hotter than the conventional adiabatic geotherm at deep lower mantle conditions. Aggregate elastic moduli and seismic velocities are also sensitive to the spin crossover and the geotherm, which impacts analyses of lower mantle velocities and composition.

References in corpus (4)

• Anomalous compressibility of ferropericlase throughout the iron spin crossover
• Thermoelasticity of Fe2+-bearing bridgmanite
• First-principles study of intermediate-spin ferrous iron in the Earth's lower mantle
• Spin crossover in (Mg,Fe${}^{3+}$)(Si,Fe${}^{3+}$)O${}_3$ bridgmanite: effects of disorder, iron concentration, and temperature

Cited by in corpus (10)

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• Deep-learning-based prediction of the tetragonal$\to$cubic transition in davemaoite
• Anharmonic thermodynamic properties and phase boundary across the post-perovskite transition in MgSiO${}_3$
• Thermodynamics of spin crossover in ferropericlase: an improved LDA+$U_{sc}$ calculation
• pgm: A Python package for free energy calculations within the phonon gas model
• Bullen's parameter as a seismic observable for spin crossovers in the lower mantle
• $\text{express}$: extensible, high-level workflows for swifter $\text{ab initio}$ materials modeling