The conference booklet for this conference is not published online, so I provide the abstract here.
Mantle phase transitions result in abrupt changes in bulk properties, including density & seismic velocities. The most significant seismic discontinuities in the mantle define the top & bottom of the Mantle Transition Zone (MTZ) at around 410 km & 660 km depth, respectively associated with the transitions Ol → Wd and Rw → Brm + Pc. However, other reactions can control the depths of the discontinuities at extremes of temperature and composition. There is a long tradition of interpreting the topography on the MTZ discontinuities in terms of temperature (e.g. Shearer & Masters, 1992). Recent studies have inverted for compositional as well as thermal variations using the amplitude of seismic reflections (Tauzin et al, 2022); highlighting the potential utility of using discontinuity topography to constrain thermo-chemical geodynamic models. Papanagnou et al (2022) predicts discontinuity topography for a thermal mantle circulation model and show that different assumptions about global mantle composition can have a dramatic effect on predicted topography but they did not consider the role of lateral compositional variation in their predicted topography.
We predict discontinuity topography from the thermochemical structure of mantle circulation models. We interpolate temperature and composition onto a finer radial grid than for the circulation simulation so when we do a mechanical mixture calculation we resolve the discontinuities. We then discriminate between geodynamic simulations based on their fit to mid-mantle discontinuity topography structure.
The transformation of bridgmanite into post-perovskite can also produce reflected seismic phases from the lowermost mantle, as could the presence of chemically distinct basal mantle structures (e.g. Sidorin et al, 1998). We attempt to use similar techniques as the above to predict what the resulting seismic discontinuity surfaces in the lower mantles of our simulations might look like, and their sensitivity to the mantle dynamics and thermochemical structure.
Papanagnou et al. (2022) https://doi.org/10.1093/gji/ggac478
Sidorin et al. (1998) https://doi.org/10.1016/S0012-821X(98)00172-1
Shearer & Masters (1992) https://doi.org/10.1038/355791a0