Spin state transition and partitioning of iron: Effects on mantle dynamics

Kenny Vilella, Sang-Heon Shim, Cinzia G. Farnetani, James Badro

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Experimental studies at pressure and temperature conditions of the Earth's lower mantle have shown that iron in ferropericlase (Fp) and in Mg-silicate perovskite (Pv) undergoes a spin state transition. This electronic transition changes elastic and transport properties of lower mantle minerals and can play an important role in mantle convection. Here we focus on the geodynamic effect of the spin-induced density modifications caused by the volume collapse of Fp and by the variation of Fe partitioning (KPv-Fp) between Fp and Pv. Since KPv-Fp behavior strongly depends on alumina content, we explore two end-member compositions, one Al-bearing (with 4.7 wt% Al2O3 in Pv) and the other Al-free. We use the theoretical model by Sturhahn et al. (2005) to calculate the spin configuration of Fp over a range of pressure-temperature conditions, and use experimental results to model Fe partitioning. We then apply the Mie-Grüneisen-Debye equation of state to obtain the density of the mineral assemblages. The calculated amplitude of the density change across the spin state transition is less than 1%, consistent with experiments by Mao et al. (2011); our density profiles differ from PREM by less than 1.5%. The spin-induced density variations are included in a three dimensional convection code (Stag3D) for a compressible mantle. We find small temperature differences between models with and without spin state transitions, since over billions of years the relative temperature difference is less than 50 K. However the relative RMS vertical velocity difference is up to 15% for an Al-free system, but only less than 6% for an Al-bearing system.

Original languageEnglish (US)
Pages (from-to)57-66
Number of pages10
JournalEarth and Planetary Science Letters
Volume417
DOIs
StatePublished - May 1 2015

Fingerprint

Earth mantle
Bearings (structural)
partitioning
Iron
mantle
perovskite
iron
Minerals
lower mantle
Geodynamics
Silicates
Temperature
temperature
Aluminum Oxide
temperature gradients
convection
Equations of state
minerals
Transport properties
mantle convection

Keywords

  • Convection
  • Earth's lower mantle
  • Fe partitioning
  • Geodynamics
  • Spin state transition

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Spin state transition and partitioning of iron : Effects on mantle dynamics. / Vilella, Kenny; Shim, Sang-Heon; Farnetani, Cinzia G.; Badro, James.

In: Earth and Planetary Science Letters, Vol. 417, 01.05.2015, p. 57-66.

Research output: Contribution to journalArticle

Vilella, Kenny ; Shim, Sang-Heon ; Farnetani, Cinzia G. ; Badro, James. / Spin state transition and partitioning of iron : Effects on mantle dynamics. In: Earth and Planetary Science Letters. 2015 ; Vol. 417. pp. 57-66.
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AB - Experimental studies at pressure and temperature conditions of the Earth's lower mantle have shown that iron in ferropericlase (Fp) and in Mg-silicate perovskite (Pv) undergoes a spin state transition. This electronic transition changes elastic and transport properties of lower mantle minerals and can play an important role in mantle convection. Here we focus on the geodynamic effect of the spin-induced density modifications caused by the volume collapse of Fp and by the variation of Fe partitioning (KPv-Fp) between Fp and Pv. Since KPv-Fp behavior strongly depends on alumina content, we explore two end-member compositions, one Al-bearing (with 4.7 wt% Al2O3 in Pv) and the other Al-free. We use the theoretical model by Sturhahn et al. (2005) to calculate the spin configuration of Fp over a range of pressure-temperature conditions, and use experimental results to model Fe partitioning. We then apply the Mie-Grüneisen-Debye equation of state to obtain the density of the mineral assemblages. The calculated amplitude of the density change across the spin state transition is less than 1%, consistent with experiments by Mao et al. (2011); our density profiles differ from PREM by less than 1.5%. The spin-induced density variations are included in a three dimensional convection code (Stag3D) for a compressible mantle. We find small temperature differences between models with and without spin state transitions, since over billions of years the relative temperature difference is less than 50 K. However the relative RMS vertical velocity difference is up to 15% for an Al-free system, but only less than 6% for an Al-bearing system.

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