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Thermoelastic properties of mantle candidate minerals are essential to our understanding of geophysical phenomena, geochemistry, and geodynamic evolutions of the silicate Earth. However, the lower-mantle mineralogy remains much debated due to the lack of single-crystal elastic moduli ( C  ij ) and aggregate sound velocities of (Al,Fe)-bearing bridgmanite, the most abundant mineral of the planet, at the lower mantle pressure-temperature ( P - T ) conditions. Here we report single-crystal  C   ij  of (Al,Fe)-bearing bridgmanite, Mg 0.88 Fe 0.1 Al 0.14 Si 0.90 O 3  (Fe10-Al14-Bgm) with Fe 3+ /ΣFe = ~0.65, up to ~82 GPa using X-ray diffraction (XRD), Brillouin light scattering (BLS), and impulsive stimulated light scattering (ISLS) measurements in diamond-anvil cells (DACs). Two crystal platelets with orientations of (–0.50, 0.05, –0.86) and (0.65, –0.59, 0.48), that are sensitive to deriving all nine  C  ij , are used for compressional and shear wave velocity ( ν  P  and  ν  S ) measurements as a function of azimuthal angles over 200° at each experimental pressure. Our results show that all  C  ij  of singe-crystal Fe10-Al14-Bgm increase monotonically with pressure with small uncertainties of 1–2% (±1σ), except  C   55  and  C  23 , which have uncertainties of 3–4%. Using the third-order Eulerian finite-strain equations to model the elasticity data yields the aggregate adiabatic bulk and shear moduli and respective pressure derivatives at the reference pressure of 25 GPa:  K  S  = 326 ± 4 GPa, μ = 211 ± 2 GPa,K   s    ′$K_{s}^{\prime}$    = ′3.32 ± 0.04, and μ′ = 1.66 ± 0.02 GPa. The high-pressure aggregate ν S  and ν P  of Fe10-Al14-Bgm are 2.6–3.5% and 3.1–4.7% lower than those of MgSiO 3  bridgmanite end-member, respectively. These data are used with literature reports on bridgmanite with different Fe and Al contents to quantitatively evaluate pressure and compositional effects on their elastic properties. Comparing with one-dimensional seismic profiles, our modeled velocity profiles of major lower-mantle mineral assemblages at relevant  P - T  suggest that the lower mantle could likely consist of about 89 vol% (Al,Fe)-bearing bridgmanite. After considering uncertainties, our best-fit model is still indistinguishable from pyrolitic or chondritic models.

Single-crystal elasticity of (Al,Fe)-bearing bridgmanite up to 82 GPa