Some surface expressions of mantle convective instabilities

Abstract

The multiple interactions between Earth’s mantle and lithosphere, which is the upper boundary layer of mantle convection, generate lateral (plate tectonics) and vertical (dynamic topography) motions of Earth's surface. Understanding the influence of the dynamics of mantle convective instabilities on the surface is fundamental to improve our interpretations of a large range of surface observations, such as the formation of sedimentary basins, continental motions, the location of hotspots, the presence of gravity anomalies or sea-level variations. This thesis aims at using numerical models of whole-mantle convection self-generating plate-like tectonics to study the impacts of the development and the dynamics of mantle convective instabilities (such as slabs or mantle plumes) on the continuous reshaping of the surface. First, I focus on the effect of the coupling between mantle convective motions and plate tectonics on the development of dynamic topography at different spatio-temporal scales. The results suggest that Earth's surface can deform over large spatio-temporal scales (> 104 km and several hundreds of millions of years) induced by whole-mantle convection to small-scales (< 500 km and five million years) arising from small-scale upper-mantle convection. I show that subduction initiation and slab break-off events control the existence of intermediate scales of dynamic topography (between 500 and 104 km). A second aim of this thesis is to understand the dynamics of mantle plumes and their interactions with surface. I first characterize in detail the behavior of mantle plumes arising in models of whole-mantle convection self-generating plate-like tectonics, in light of surface observations. Then, I quantify the lateral motions of mantle plumes and unravel the sources of their drift. Finally, I use observations of the mantle thermal signature of plume/ridge interactions to reconstruct the relative motions between the Azores mantle plume and the Mid-Atlantic Ridge.