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Adina Pusok, Oxford University    

The theory of plate tectonics established fifty years ago has formed a robust framework for understanding how the Earth works across a range of scales. While the kinematics of plate tectonics is well established, the dynamics remain a challenge. A key component is understanding the nature of the oceanic lithosphere–asthenosphere system. The classic view suggests that mid-ocean ridges (MORs) are places of passive mantle upwelling driven by plate divergence, and that the oceanic lithosphere forms by conductive cooling away from the ridge axis. Melt represents a passive component in this model – a view that has been questioned by recent seismic and magnetotelluric data from the sea floor. Here I present two-phase flow numerical models of MORs and oceanic lithospheric extension that highlight the dynamic role of melt in the oceanic lithosphere–asthenosphere system. In a first part, I show that melting-induced buoyancy effects may induce time-dependent flow and provide an explanation for both the asymmetric distribution of melt beneath the axis and the inferred short-wavelength variations in the lithosphere–asthenosphere boundary (LAB). In a second part, I show some preliminary results using a new poro-viscoelasto-viscoplastic theory that allows for the formation and evolution of fluid-driven fractures, such as dikes and sills. I investigate how magma interacts with the solid-rock closer to the MOR axis, and whether magma supply controls fragmentation of oceanic lithosphere. Finally, these results were obtained using the FD-PDE framework, which is a computational framework for building flexible, testable and robust geodynamic models.