Strong seismic anisotropy observed in the Earth's lowermost mantle, the D″ layer, is likely attributed to the lattice-preferred orientation (LPO) of its predominant mineral, magnesium-silicate post-perovskite (PPv). Here we report simultaneous high-pressure and -temperature plastic deformation experiments on MnGeO3 PPv from 77 to 111 GPa and from 83 to 105 GPa at 2000 K using the membrane-type diamond-anvil cell (DAC). Radial X-ray diffraction measurements demonstrate that the (001) plane aligned perpendicular to the compression direction, indicating deformation dominated by slip on (001). In strong contrast to other slip planes proposed previously, the (001) slip plane can cause significant shear-wave splitting with polarization in line with seismic observations. D″ anisotropy can therefore be primarily reconciled with LPO of the PPv phase.
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