The Thickness of Phase Transformation Layers in the Earth’s Mantle

  • Jacek Leliwa-Kopystyński
Part of the Ettore Majorana International Science Series book series (EMISS, volume 11)

Abstract

The most important phase transformations in the Earth’s mantle are those related to silicates of magnesium and iron at depths of about 400 km (olivine → spinel transformation) and 650 km (Mg2SiO4 spinel → 2 MgO periclase + SiO2 stishovite transformation according to Sung and Burns (1975) and Navrotsky (1977), or transitions of MgSiO3 leading to a perovskite structure according to Liu (1977)). In spherically symmetric models of the Earth (e.g. in model 1066B of Gilbert and Dziewoński, 1975) phase transformations correspond to the surface of discontinuity in density p and seismic wave velocities vP and vS. There are several causes which might change the position depth of phase equilibrium surfaces or which might transform those surfaces into layers with a defined thickness:
  1. (i)

    Differences in regional temperature distributions in the mantle induce deviations of phase equilibrium surfaces from the spherically symmetrical shape.

     
  2. (ii)

    A complex mineral composition of transformable materials (e.g. olivine(Mgx Fe1−)2SiO4, x ≃0.9) results in the formation on the p, T (pressure, temperature) plane, instead of the phase equilibrium line determined by the Clausius-Clapeyron equation, of an area of low- and high-pressure phase coexistence in the Earth’s interior (Fig. 1, a).

     
  3. (iii)

    In areas with vertical displacements (mid-oceanic ridges, subduction zones) phase transition kinetics leads to the transformation of the equilibrium surfaces into a layer even for minerals of simple chemical composition like Mg2SiO4 (Fig. 1, b).

     

Keywords

SiO2 Magnesium Silicate Posit Olivine 

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References

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Copyright information

© Plenum Press, New York 1981

Authors and Affiliations

  • Jacek Leliwa-Kopystyński
    • 1
  1. 1.Institute of Geophysics Polish Academy of SciencesPasteura 3Poland

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