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

Abstract

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-perovskite1,2. Observations of seismic anisotropy within the D′′ region are inferred to arise from textures within post-perovskite3,4,5 that are created by flow in the deep mantle. Specifically, mantle flow is thought to cause post-perovskite to deform, creating a lattice-preferred orientation within the post-perovskite6,7,8,9,10. 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 system11 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 lower-mantle 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.