The impact of Pangean subducted oceans on mantle dynamics: Passive piles and the positioning of deep mantle plumes

Seismic imaging of the Earth's interior reveals plumes originating from relatively hot regions of the lowermost mantle, surrounded by cooler material thought to be remnants of ancient subducted oceans. Currently, there is no clear consensus on the internal composition of the hot regions, with end-member conditions being that they are thermo-chemical in nature or purely thermal plume clusters. Previous modelling studies have shown a range of scenarios where deep chemical heterogenities or purely thermal anomalies are essential in developing appropriate present-day mantle dynamics. Here, we add to this discussion by quantifying the location of rising mantle plumes using numerical 3-D global mantle convection models constrained by 410 million years of palaeo-ocean evolution (encompassing the formation and breakup of supercontinent Pangea). Our study compares numerical simulations with purely thermal convection to those where a deep thermo-chemical anomaly is laterally mobile. The results show that models both with and without large-scale chemical heterogeneities can generate appropriate present-day plume dynamics, which illustrate the power of sinking ocean plates to stir mantle ow and control the thermal evolution of the mantle. Our models add to the discussion on bottom-up and top-down mantle dynamics, indicating the difficulty in unravelling the processes using numerical models alone.