Earth’s dynamic topography evolution during the last 200 Myr: Insights from mantle convection models with imposed plate motions.

Abstract

The convective motions of Earth's mantle have a profound influence on its surface. One such surface expression that is dynamically influenced by the mantle is the elevation of the relief. While this is largely controlled by isostasy, the static component of elevation that is determined by the gravitational balance of the lithosphere and asthenosphere, the effects of dynamic topography can contribute up to 1000 m of elevation or subsidence. In a global study we examine how much various regions on Earth's surface are affected and how their location with respect to their changing tectonic setting over time rules their elevation history. We find that they categorise in mainly three distinct classes, where subduction zone vicinity plays a crucial role for their subsidence, such that, like in the case of Australia, the two closest subduction zones play a mutually dominant role in dynamic support over the observed time period. These results are underpinned by a cluster analysis. In order to assess how these findings vary with different set-ups of our numerical model, we explore the sensitivity of our results regarding the prescribed viscosity profile of the mantle and different initial conditions. We find a strong correlation between plate kinematics and mantle flow across all simulations, varying with the degree of heterogeneity of the mantle structure. If plumes are allowed to develop, they entrain upwards flow, thereby reducing passive return flow. We find that this passive return flow is responsible for over-prediction of dynamic support. Moreover, active upwellings act to reduce the degree two dominance of the dynamic topography pattern. Spectral analysis of the models and global observations clearly shows the deep mantle influence of dynamic support and the dominance of return-flow due to mass balance in numerical simulations. Thus, introduction of more realistic geodynamic models overcomes shortcomings of geodynamic modelling of dynamic topography.