Strong inheritance of texture between perovskite and post-perovskite in the D" layer

About 200 km above the core-mantle boundary, the D '' seismic discontinuity marks the depth where magnesium silicate perovskite-the main mantle mineral-is transformed into its high-pressure phase of post-perovskite(1,2). Observations of seismic anisotropy within the D '' region are inferred to arise fromtextures within post-perovskite(3-5) that are created by flow in the deep mantle. Specifically, mantle flowis thought to cause post-perovskite to deform, creating a lattice-preferred orientation within the post-perovskite(6-10). However, it is difficult to explain all of the observed patterns of seismic anisotropy in the D '' region from this deformation mechanism alone. Here we use a low-pressure fluoride analogue system(11) to study the transformation from perovskite to post-perovskite in laboratory experiments. We find that post-perovskite can inherit texture from the perovskite phase. If a similar transformation mechanism operates in the Earth, post-perovskite will inherit textures from deformed perovskite and vice versa, as lowermantle material passes into and out of the D '' region. We find that this textural inheritance, combined with lattice-preferred orientation in post-perovskite, can explain the observed patterns of anisotropy in the lowermost mantle.