On the Dynamics of Plate Tilting: An Analytical and Numerical Approach

Abstract

The Earth’s topography is dynamically evolving through the vertical motion of tectonic plates. This impacts evolution of sedimentary basins which are the Earth’s billion-year history tablets for sea-level variations, climate change and evolution of species. These sedimentary basins are also major sources for coal, oil, gas and water. To unravel the Earth’s geodynamic history and make better predictions about the Earth’s resources, it is of critical importance to understand how the Earth’s topography responds to the interaction between plates and the underlying mantle. Existing predictions for amplitude of dynamic topography derived from global mantle convection models don’t agree well with dynamic topography amplitudes derived from investigations based on sedimentary basins and ocean bathymetry. In this thesis, it is proposed that at shorter wavelengths (<1,000 km) the predictions for dynamic topography amplitude driven by upper mantle density anomalies can be improved by considering the non-Newtonian rheology of rocks. Furthermore, existing mantle convection models, hitherto, cannot explain the long-wavelength rapid subsidence/uplift of sedimentary basins. This problem is addressed by simple analytical models, and by 2D thermo-mechanical numerical experiments taking into account the progressive mechanical transition between the plate and the underlying mantle. The results indicate that horizontal plate motions are associated with gradients in basal shear stress and normal stress, the latter dominating the plate tilt. A critical finding is that plate tilting is relatively fast with uplift/subsidence rates of about few 100 m Myr-1. The numerical model results also suggest that during plate motion, the trailing edges of the plates are being compressed, which might shed light on the tectonic inversion of passive margins.