Probing the lower mantle composition and thermal structure: Insights from D``

Earth's lower mantle, although key to understanding both large-scale mantle dynamics and the global geochemical cycle, remains highly enigmatic. Some clues to its nature can potentially come from studies of the D`` region, believed to represent the perovskite to post-perovskite phase transition. To the first order, the thickness of this region of post-perovskite stability can be predicted thermally, allowing for the expected locations of seismic D`` observations to be mapped out. However, comparing these predictions to a new compilation of D`` seismic observations, discrepancies appear. In particular, D`` is observed within the Pacific LLSVP, where thermal models indicate that the transition to post-perovskite should not occur. We hypothesize that this is due to a difference in composition within the Pacific LLSVP. Through compilations of mineral physics data, we can begin to explore the effect that composition can have on both the calculation of the lower mantle thermal structure and on the conditions of post-perovskite stability in the lower mantle.