Understanding the Role of Plate History and Rheology in the Geodynamical Prediction of Thermochemical Piles

Conceptual thermochemical mantle models which include the presence of a large volume of more-dense material in the lower mantle have recently gained favor due to improved observational and modeling studies. One such model in particular involves the presence of long-lived, stable thermochemical piles that reside in the lowermost beneath Africa and the Pacific. Previous work has shown that this model appears to be geodynamically consistent with Earth's subduction history over the past 120 million years, although geodynamical consistency alone does not exclude other mantle models. Because we are geologically limited in terms of how far back we can examine Earth's subduction history, it is important to ascertain how this missing plate history data (pre 120 Ma) affects our geodynamical predictions. Here, we perform numerical thermochemical convection calculations that focus on understanding how Earth's past subduction history affects the predicted shape and positions of proposed thermochemical piles and how these compare to seismic tomography models. We also investigate the role that viscosity structure has on the morphology of predicted thermochemical structures.