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Metsue, A. & Tsuchiya, T., 2012. Thermodynamic properties of (Mg,Fe2+)SiO3 perovskite at the lower mantle pressures and temperatures: An internally consistent LSDA+U study (Geophys. J. Int., 190, 310–322)

We have found a mistake in our calculations of the phase diagram of perovskite (Pv) and post-perovskite (PPv) in a (Mg0.9375Fe0.0625)SiO3 composition as presented in Metsue & Tsuchiya (2012). Although a substantial reduction in the transition pressure due to the iron incorporation was proposed (figs 5 and 6 of the original paper), in fact this was due to a small error; a correct calculation shows that the effect of iron is much less. However, the error has almost no effect on the width of Pv-PPv coexisting pressures or the slope of phase boundary. The corrected Gibbs free energy relationships and phase diagram are presented here in Figs 1 and 2, respectively.

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Figure 1. Corrected total Gibbs free energy of solid solution (Gss) of Pv and PPv at 116 GPa (a) and 121 GPa (b) at 3000 K relative to the end-members of Pv phase. We show the case of Pv and PPv coexistence in (b). The cotangent of the two curves (green line) gives the fraction of Fe in Pv and PPv (dashed green lines). This corrects fig. 5 of Metsue & Tsuchiya (2012).

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Figure 2. Corrected high-P,T phase diagram for a (Mg0.9375Fe0.0625)SiO3 composition in the lowermost mantle condition. Green line is the normal adiabatic geotherm of Brown & Shankland (1981). The blue line is the geotherm with thermal boundary layer thickness of 400 km proposed by Kawai & Tsuchiya (2009). The shaded domain represents the coexisting region of the Pv and PPv phases. Orange line represents the boundary for pure MgSiO3 calculated by Tsuchiya et al. (2004). The vertical dotted line represents the core-mantle boundary pressure (135 GPa). Experimental studies for the (Mg0.91Fe0.09)SiO3 composition (pink lines) (Catalli et al. 2009) and the San Carlos olivine composition (blue lines) (Grocholski et al. 2012) are also indicated for comparison. This corrects fig. 6 of Metsue & Tsuchiya (2012).

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The corrected phase diagram presented in Fig. 2 shows that Fe still slightly decreases the Pv-to-PPv phase boundary at lower temperatures. Along the normal mantle geotherm proposed by Brown & Shankland (1981), the transition starts at 114 GPa and ends at 119 GPa. Along a hotter geotherm with ∼500 K higher temperatures, the transition starts at 121 GPa and ends at 124 GPa. At these temperatures, we find the transition pressure of (Mg0.9375Fe0.0625)SiO3 is quite comparable to that of pure MgSiO3 (Tsuchiya et al. 2004). Therefore, we can now state that lateral temperature heterogeneity near the core-mantle boundary can affect the Pv-to-PPv transition condition, as the transition occurs at deeper depth in hotter regions, unlike in the original paper.

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