The influence of asthenospheric flow under cratonic keels on intraplate stress field and dynamic topography

In the present work, we used thermo-mechanical numerical models with realistic rheology for the crust and mantle to assess how the asthenospheric flow under cratonic keels affected the topography and intraplate stress field. We tested different thickness values for the cratonic keel and the relative speed between the lithosphere and the base of the upper mantle. We observed that the horizontal flow of the asthenosphere under the cratonic keel induces extensional stresses in the crust when the asthenospheric flow occurs from the thinner lithosphere towards the craton, defined here as the “cratonic bow”. On the other hand, compressional stresses in the crust are observed in the region where the asthenospheric flow occurs from the craton towards the thinner lithosphere, a portion defined here as the “cratonic stern”. The magnitude of the stresses increases with higher speeds and a thicker cratonic keel, reaching a magnitude of ∼10MPa in the cratonic crust in the scenarios with a cratonic keel with 200 km in thickness. The asthenospheric flow under the cratonic keel induces edge-driven convection with larger vigor adjacent to the cratonic stern, where topographic perturbations are observed, especially in scenarios with a thick cratonic keel, resulting in negative dynamic topography of hundreds of meters. We propose that this mechanism of dynamic subsidence can explain part of the negative residual topography observed along the southern Australian margin, induced by the fast (∼7.4 cm/year) northward movement of the plate combined with the presence of a thick lithospheric keel in the continent.