The Post‐Perovskite Transition in Fe‐ and Al‐Bearing Bridgmanite: Effects on Seismic Observables

The primary phase of the Earth’s lower mantle, (Al, Fe)-bearing bridgmanite, transitions to post-perovskite (PPv) at deep mantle conditions. Despite extensive experimental and ab initio investigations, there are still important aspects this transformation that need clarification. Here, we address transition in (Al3+, Fe3+)-, (Al3+)-, (Fe2+)-, (Fe3+)-bearing bridgmanite using calculations validate our results against experiments on similar compositions. Consistent with experiments, show onset pressure width two-phase region depend distinctly chemical composition: (a) Fe3+-, Al3+-, or Fe3+)-alloying increases pressure, while Fe2+-alloying has opposite effect; (b) absence coexisting phases, pressure-depth range Pv-PPv is likely too broad cause a sharp D” discontinuity (<30 km); (c) average Clapeyron slope regions consistent previous measurements, MgSiO3, inferences from seismic data. In addition, (d) observe softening bulk modulus region. consistency between gives us confidence proceed examine aggregates different compositions computationally, which will be fundamental for resolving most composition D" by analyses tomographic images.