Process of Obduction in Global Mantle Convection Models

Abstract:

Convergent plate tectonic boundaries where a denser oceanic lithosphere is deposited on top of a less dense continent in an obduction process represent enigmatic regions with unexplained origin. So far, numerical and experimental studies in regional settings have been mostly employed in order to decipher which parameters control the obduction to happen and favor its feasibility. However, plate motions are driven by forces that originate in the interior of the Earth. Regional models neglect this large scale dynamics while imposing prescribed and forced compression of the system. In this study, we investigate obduction in global mantle convection models using 2D thermo-chemical numerical simulations in spherical annulus geometry. The convection models are characterised by Earth-like plate tectonics and include mobile continents. At the convergent boundaries in between oceanic and continental lithosphere, obduction is allowed to occur due to imposed free surface conditions. We investigate the setting favorable for the emplacement of denser rock on top of the lighter continent and the impact of large scale forces on obduction. We then vary critical parameters of continental strength and the thickness of the continental edges to infer how these influence the system and compare its first order characteristics with available geological record.