Anomalous compressibility of ferropericlase throughout the iron spin cross-over

R. M. Wentzcovitch, J. F. Justo, Z. Wu, C. R.S. Da Silva, D. A. Yuen, D. Kohlstedt

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The thermoelastic properties of ferropericlase Mg1-xFe xO (x = 0.1875) throughout the iron high-to-low spin cross-over have been investigated by first principles at Earth's lower mantle conditions. This cross-over 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 at ≈1,400-1,600 km depth. This anomaly might also cause a reduction in the effective activation energy for diffusion 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.

Original languageEnglish (US)
Pages (from-to)8447-8452
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number21
StatePublished - May 26 2009


  • Earth's lower mantle
  • Thermal expansivity
  • Thermodynamics
  • Viscosity


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