Dynamic topography of continents and rotational stability of planets with lithospheres

This thesis examines two distinct topics related to the long-term evolution of terrestrial planets. The first, dynamic topography, is the vertical motion of the Earth’s tectonic plates in response to viscous stresses in the mantle driven by connective processes. Using mantle flow modelling, I show how dynamic topography linked to plate subduction can explain a long-wavelength component of sediment deposition in the Silurian Baltic Basin. Simulations constrain the paleo-dip angle of subuction to 40-60 degrees and show that the slab-induced mantle flow mechanism provides 40-85% of the near-field sediment deposition. In another regional study, I use convection simulations constrained by seisemic tomography to reconcile the observed broad tilting of the present-day Arabian platform that extends from the Red Sea to the Persian Gulf. This area has been cited as a classic example of rift-flank uplift; however the influence of the rift-flank processes is largely limited to uplift within a few hundred kilometers of the margin. Density heterogeneities linked to a megaplume, which are responsible for high topography in Southern Africa and rifting in East Africa, can reconcile the anomalous topography seen in Arabia. The second topic in this thesis deals with the rotational stability of planets with lithospheres. Using an equilibrium rotational theory suitable for a planet with a lithosphere characterized by long-term elastic strength, along with observational constraints on the figure of Mars, I show that the current rotation axis of Mars is stable. I also find that development of the massive Tharsis volcanic province cause a reorientation of the planet that was likely less than 15 degrees and that the thickness of the elastic lithosphere at the time of Tharsis formation was at least ~ 50km. Finally, I extend the equilibrium theory for a planet with an elastic lithosphere to consider the effect of a viscoelastic lithosphere on rotational stability. I find that the sufficiently high lithospheric viscosities (5x10(24) Pa-s of greater) a viscoelastic lithosphere can have a significant impact on reducing rates of true polar wander induced by an uncompensated load. These rates depend on the viscosity of the lithosphere and the size of the load.Ph.D