bulk compositions (b). Color shading indicates the relevant parts of each diagram for different bulk compositions (a) or exchange coefficients (b). Note the reduction in the Fe‐Mg exchange coefficient between bridgmanite and ferropericlase with increasing pressure as predicted by thermodynamic modeling based on DFT computations.
To evaluate the impact of variations in rock composition and thermal state of the lower mantle on seismic properties, I computed P‐ and S‐wave velocities for pyrolite, harzburgite, and metabasalt over relevant pressure and temperature intervals. Recent experimental and computational results on the high‐pressure and high‐temperature elasticity of lower‐mantle phases are compiled in Table 3.1. This compilation aims at reflecting recent progress on individual mineral phases and does not represent an internally consistent data set in a thermodynamic sense. If not given in the original publication, finite‐strain and thermal parameters were determined by fitting experimental data to the finite‐strain formalism of Stixrude & Lithgow‐Bertelloni (2005). I included the effect of spin transitions of Fe2+ in ferropericlase and of Fe3+ in bridgmanite and in the CF phase using the parametrization introduced in Section 3.7 with parameters given in Figures 3.5a–c. The effect of the ferroelastic phase transition from stishovite to CaCl2‐type SiO2 was modeled based on the reanalysis of powder diffraction data (Andrault et al., 2003) using Landau theory as given by Buchen et al. (2018a). The experimentally determined phase boundary between stishovite and CaCl2‐type SiO2 with a Clapeyron slope of dP/dT = 15.5 MPa K–1 (Fischer et al., 2018) was used to constrain the temperature dependence of the Landau parameter A. Figure 3.7 shows P‐ and S‐wave velocities for each mineral composition in Table 3.1 along a typical adiabatic compression path.
Table 3.1 Finite‐strain parameters for mineral phases of the lower mantle.
References: [1] Fiquet et al. (2000), [2] Murakami et al. (2007), [3] Zhang et al. (2013), [4] Murakami et al. (2012), [5] Chantel et al. (2012), [6] Fu et al. (2018), [7] Jackson et al. (2005), [8] Kurnosov et al. (2017), [9] Sinogeikin & Bass (2000), [10] Murakami et al. (2009), [11] Yang et al. (2016), [12] Yang et al. (2015), [13] Thomson et al. (2019), [14] Mookherjee (2011), [15] Stixrude & Lithgow‐Bertelloni (2011), [16] Imada et al. (2012), [17] Dai et al. (2013), [18] Wu et al. (2017), [19] Andrault et al. (2003), [20] Jiang et al. (2009), [21] Gréaux et al. (2016), [22] Fischer et al. (2018), [23] Buchen et al. (2018a).
| Mineral/Phase | Formula | Volume | Bulk modulus | Shear modulus | Quasi‐harmonic parameters | References | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| V 0 (Å3) | K 0 (GPa) | K 0 ' | G 0 (GPa) | G 0 ' | θ 0 (K) | γ 0 | q 0 | η S0 | |||
| bridgmanite | MgSiO3 | 162.27(1) | 253(9) | 3.9(2) | 173(2) | 1.56(4) | 905.9 | 1.44 | 1.09 | 2.2(2) | [1,2,3,4] |
| (Mg0.95Fe0.05)SiO3 | 163.45(2) | 247(2)S | 3.6(1) | 168.3(9) | 2.02(3) | 905.9 | 1.44 | 1.09 | 2.2 | [3,4,5*,6*] | |
| (Mg0.96Al0.04)(Si0.96Al0.04)O3 | 163.21(1) | 252(5)S | 3.7(3) | 166(1) | 1.57(5) | 905.9 | 1.44 | 1.09 | 2.2 | [3,4,7] | |
| (Mg0.9Fe0.1)(Si0.9Al0.1)O3 | 162.96(2) | 250.8(4)S | 3.44(3) | 159.7(2) | 2.05(2) | 905.9 | 1.44 | 1.09 | 2.2 | [3,4,8] | |
| ferropericlase | MgO | 74.68(2) | 163(1)S | 3.8(1) | 131(1) | 1.92(2) | 770 | 1.5 | 2.8 | 3.0 | [9,10,11*] |
| (Mg0.92Fe0.08)O | 74.07(1) | 169(2)S | 4.01(7) | 126(2) | 2.08(3) | 770 | 1.5 | 2.8(6) | 3.0(3) |
[11*,12
|