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Ziqi Ma (Maggie)

“Explore 3D numerical models of plume-lithosphere interaction and plume-ridge interaction using a modified version of mantle-convection code CITCOM"

PhD project title:

New Insights into Global Plume Buoyancy and Heat Fluxes from Numerical Models of Plume-Lithosphere Interaction.


 
Ziqi Ma Maggie
Project description:

Earth's dynamical evolution is controlled by the interplay between mantle convection and plate tectonics. While subducted plates stir the mantle, upwelling plumes can lubricate, push, and break up plates. As the surface expression of upwelling plume dynamics, the buoyancy flux is traditionally estimated as the cross-sectional area of the hotspot swell multiplied by overriding plate velocity (for intraplate hotspots) or multiplied by the full-spreading rate (for ridge-centered hotspots).

This classical approach implies that the swell is fully isostatically compensated by the hot ponding plume material at the base of the lithosphere and that this plume material spreads at exactly the same speed as the overriding plate moves. However, geophysical observations and numerical model predictions demonstrate that this assumption is usually wrong: hotspot swells are largely dynamically compensated and, to some extent, also compensated by sublithospheric erosion; moreover, plumes typically spread faster than plate motion. Evidence in the North Atlantic from prominent V-shaped ridges, ephemeral landscapes, and off-axis uplift of oceanic gateways suggest that along-axis plume velocities in the asthenosphere can be an order of magnitude faster than the full plate-spreading rate. Thus, classical estimates for the buoyancy fluxes of deep-seated mantle upwellings are strongly biased by surface-plate velocities. As detailed estimates of dynamic seafloor topography have recently become available, now is the time to revisit the buoyancy fluxes and thereby the mass and heat fluxes carried by mantle plumes.

In this project, we will explore 3D numerical models of plume-lithosphere interaction and plume-ridge interaction using a modified version of mantle-convection code CITCOM. Synthetic bathymetry will be computed from normal stresses at the model's top boundary. We aim to quantify plume spreading and hotspot swell support for various conditions, putting further constraints on the heat and buoyancy fluxes of individual plumes and all plumes globally.