Seismic shear wave anisotropies are observed in Earth痴 uppermost lower mantle around subduction zone. The anisotropy caused by the deformation-induced crystallographic preferred orientation (CPO) of bridgmanite (perovskite-structured (Mg,Fe)SiO3) is the most plausible explanation for these seismic observations. However, the rheological properties of bridgmanite are largely unknown because of experimental difficulty.
In this study, we report the CPO pattern and dominant slip system of bridgmanite under conditions that correspond to the uppermost lower mantle (25 GPa and 1,873 K) obtained through simple shear deformation experiments. The fabrics obtained are characterized by  perpendicular to the shear plane and  parallel to the shear direction, implying that the dominant slip system of bridgmanite is (100). The observed seismic shear wave anisotropies near several subducted slabs can be explained in terms of the CPO of bridgmanite as induced by mantle flow parallel to the direction of subduction. (12, Dec., 2016)
Tsujino, N., Nishihara, Y., Yamazaki, D., Seto, Y., Higo, Y., Takahashi, E., Mantle dynamics inferred from the crystallographic preferred orientation of bridgmaniten, Nature, 2016. Abstract (Nature Online)
Figure 1: Crystal stracture of bridgmanite.
Figure 2: Schematic cross-sections of subducted slab at Tonga-Kermadec arc.