Dynamics of Mantle Plumes and Their Influence on Paleotopography

The present-day structure of the Earth’s mantle, as revealed by an array of geophysical and geochemical observations, features plumes that rise from the deep lower mantle to the base of the lithosphere. Arrival of plume heads beneath the lithosphere is associated with the formation of large igneous provinces on the Earth’s surface. Following the eruption of a plume head, long-lived plume tails are responsible for continued magmatism associated with volcanic hotspot tracks, while dynamic topography associated with their interactions with continental lithosphere bears important implications for the evolution of paleotopography. This thesis investigates the spatial distribution of mantle plumes that erupted over the last 200 Myrs, their subsequent lateral migration and their influence on paleotopography. We investigate the influences of lower mantle chemical heterogeneities on the nucleation and eruption of plumes in paleogeographically constrained global models of mantle convection spanning the last 200 Myrs. We show that plume eruption locations in models with a chemically anomalous lower mantle are highly correlated with reconstructed eruption locations of large igneous provinces that erupted over the last 200 Myrs — those in purely thermal models show a weaker correlation. Plumes in thermochemical models are anchored to peaks of ridges extant within large-scale thermochemical structures that can morph and migrate laterally in response to subduction-induced flow. Subsequently, we derive spatiotemporal analytics of flow in the deepest lower mantle and show that edges of these thermochemical structures can undergo rapid asymmetric deformation in regions of strong coherent subduction-induced flow. Consequently, rapid motion of plume sources anchored to these regions causes the plumes to become strongly tilted. We show that the sharp bend in the Hawaiian-Emperor hotspot track is a consequence of the interplay of plume tilt and lateral advection of plume source. Asymmetric deformation of the thermochemical structure under the Pacific over the last 140 Myrs may explain the morphological diversity of surface hotspot tracks associated with deep mantle plumes in the Pacific. Moreover, we show that analogous flow dynamics caused the Afar plume and the thermochemical structure under Africa to migrate southward over the lifetime of the plume. Our analysis suggests that the space-time distribution of plume-related magmatism in east Africa and the associated trends in geochemical data are better explained by a moving Afar plume. We develop a new scalable code to investigate the influence of transient plume-related dynamic topography on the evolution of paleodrainage systems. Based on simple qualitative models of geomorphology, we suggest that a dynamic topography swell associated with the southward propagating Afar plume may have induced a reorganization of regional paleodrainage systems in east Africa