Mantle Convection and Surface Expressions. Группа авторов

^*] Ca silicate perovskite CaSiO₃ 45.57(2) 248(3) 3.6(1) 107(1) 1.66(22) 771(90) 1.67(4) 1.1(2) 3.3 [13] Ca ferrite‐type phase MgAl₂O₄ 236.07 217 3.7 133 1.7 840(20) 1.3(3) 1(1) 2(1) [14,15] FeAl₂O₄ 247.49 217 3.7 133 1.7 840 1.3 1 2 [14,15] Na_0.4Mg_0.6Al_1.6Si_0.4O₄ 239.9(37) 221(2) 4 129.65(6) 2.34(1) 840 1.3 1 2 [15,16,17] Na_0.88Al_0.99Fe_0.13Si_0.94O₄ 242.79(27) 205(6) 3.6(2) 130 2 840 1.3 1 2 [15,18^*] stishovite SiO₂ 46.51(2) 320(2) 4 264(2) 1.90(1) 1100 1.7 5.7(3) 2.9(2) [19,20,21^*,22,23] CaCl₂‐type SiO₂ SiO₂ 47.54(18) 238(6) 4.82(2) 264(2) 2.23(1) 1100 1.7 5.7 2.9 [19,20,21^*,22,23]

      Values in italics were estimated or adopted from other compositions/polymorphs of the same phase/compound.

^S Isentropic bulk modulus.

^* Original data were refit to the finite‐strain formalism of Stixrude & Lithgow‐Bertelloni (2005).

Figure 3.7 P-wave (a) and S-wave (b) velocities for different mineral phases and compositions along a typical adiabatic compression path starting at 1900 K and 25 GPa (see Figure 3.8). These mineral phases and compositions were mixed to model elastic wave speeds of rocks as shown in Figures 3.8 and 3.9. Dashed curves show P‐ and S‐wave velocities when the effect of relevant continuous phase transitions on elastic properties is ignored. See Table 3.1 for references.

      Chemical bulk compositions for pyrolite and metabasalt were approximated by the depleted MORB mantle (DMM) and NMORB compositions of Workman and Hart (2005). In analogy to the approach of Xu et al. (2008), a hypothetical harzburgite composition was generated by assuming pyrolite to be an 80:20 mixture of harzburgite:basalt by mass. A basalt fraction of 20% in the mantle corresponds to the upper limit of estimates based on geochemical (Morgan & Morgan, 1999; Sobolev et al., 2007) and geodynamical arguments (Ballmer et al., 2015; Nakagawa et al., 2010). For pyrolite and harzburgite, mineral compositions were computed in the system CFMAS and for metabasalt in the system NCFMAS. Bulk compositions were partitioned into the phase assemblages bm‐fp‐cp for pyrolite and harzburgite and bm‐cp‐cf‐st for metabasalt resulting in approximate volume fractions of 77:16:7 (bm:fp:cp) in pyrolite, 74:24:2 (bm:fp:cp) in harzburgite, and 45:26:14:15 (bm:cp:cf:st) in metabasalt, respectively. For each phase, the compositions listed in Table 3.1 were mixed to match the computed mineral compositions as outlined in Section 3.6. For some mineral compositions, this approach required extrapolations beyond the compositional limits defined by the mineral compositions in Table 3.1. In these cases, the extrapolations of elastic moduli were restricted to not transcend compositional limits by more than 10% of the compositional range delimited by the mineral compositions of Table 3.1.

      The exact mineral compositions and volume fractions for a given bulk rock composition depend critically on assumptions