Asthenospheric Flow and Evolution of Continental Margins

Abstract

At the surface of the Earth, tectonic plates move at a speed of a few centimetres per year relative to the underlying hotter asthenosphere. As it flows underneath and around the base of continents, the hot asthenosphere has the potential to mechanically and thermally erode the thicker, cooler lithospheric mantle, while imposing shear tractions on the edges of the continents and promoting intra-plate volcanism (Conrad et al., 2011). Mechanical and thermal effects must be stronger along the steep lithosphere edges that exist underneath thick continents. Previous studies have shown that there is a contrast between the leading edge of the continent, which faces the full force of the asthenosphere flow, the trailing edge, which largely escapes the flow of hot asthenosphere, and the lateral edges mainly exposed to toroidal flow (e.g. Farrington et al., 2010; Davies and Rawlinson, 2014). To assess the thermal and mechanical consequences of asthenosphere flow on the evolution of continental margins we have performed a series of 2D and 3D, coupled thermo-mechanical, numerical experiments including realistic temperature, stress, strain, strain rate, and melt dependent rheologies. We simulate a composite continent/ocean tectonic plate moving above a hotter asthenosphere. We use Underworld to solve Stokes equation for a very low Reynolds number (i.e. low ratio inertial to viscous forces) on a Cartesian grid at the node of which velocity, pressure and temperature are solved. Lagrangian particles, on which stress, density and viscosity are updated, represent materials advected through the fixed Cartesian mesh. A user-specified constitutive tensor, accounting for plastic-viscous rheology, relates stress and strain rate. Our results suggest that for significant plate velocities, the leading edge and the trailing edge of thick continents record contrasting thermal and mechanical histories that impact on the evolution of continental margins. By modulating temperature and shear traction along continental margins, the relative motion between continents and the asthenosphere impacts on the rheology of continental margins, and promote dynamic uplift or subsidence which impacts on the evolution of sedimentary basins.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015