Numerical Models of Mantle Convection and Plate Tectonics

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Richards EAR-0003553 Geodynamicists have recently crossed a significant threshold by showing that plate tectonic styles of mantle convection arise self-consistently in numerical models that include simple rheological descriptions of lithospheric failure. The investigators propose to further develop 3-D spherical models of mantle convection and plate tectonics to include a more complete physical treatment of lithospheric failure, or plate boundary formation. They will use a tensor extension of scalar "damage theory" to account for enhanced weakening oriented according to maximum shear strain. A reasonable and significant hypothesis is that alternating ridge-transform geometries arise naturally in such models, and that the one-sidedness of subduction zones may also be related to oriented strain-rate weakening deep within fault zones. An anisotropic formulation of lithospheric failure rheology requires Lagrangian tracking, or advection, of tensor viscosity -- a non-trivial task facilitated by methods they have developed for tracking chemical species in mantle convection. The investigators also propose to continue their focussed investigation into the role of a pronounced sublithospheric low viscosity zone (LVZ) in promoting plate tectonics. Other related work supported by this grant will include ongoing studies of mantle mixing, thermal coupling of the core and mantle, the dynamics of diffuse plate boundaries, and interactions of thermo-chemical plumes with plate-scale flow.