Proxies for the presence of post-perovskite in the lowermost mantle based on seismic tomography and geodynamic modelling

The post-perovskite (pPv) phase is often invoked as an explanation for seismic observations of discontinuities, anisotropy and anti-correlation between velocities in the lower mantle. Accurate interpretations of these features in terms of pPv are important, as the phase transition provides a much-needed temperature probe in the lowermost mantle. Robust observations of this phase transition have the potential to constrain the temperature of and heat flow across the core-mantle boundary and thus provide estimates of the heat budget and thermal evolution of the Earth.

Traditionally, the presence of post-perovskite (pPv) has been inferred from observations of seismic discontinuities in the lowermost mantle. However, these only give a very patchy image of lateral variations in the presence of pPv due to the heterogeneous coverage of seismic data. In addition, interpretations are complicated by the fact that the properties and stability field of pPv remain uncertain from a mineral physics point of view.

Here, we describe different proxies for the presence of post-perovskite, proposed based on global seismic tomography. To investigate their accuracy, we utilize synthetic tomography models derived from geodynamic modelling in combination with mineral physics and we compare the predicted presence to the true occurrence of pPv in the model. By using both high-resolution geodynamic models as well as filtered models that have been corrected for the limited resolution of seismic tomography, we can investigate whether a proxy works in theory (on the high-resolution versions) and also in practice (on the filtered models). We will discuss how we may be able to constrain the stability field of pPv based on comparisons with published tomographic models and make recommendations as to what has to improve in seismic tomography to make different proxies work.