Irina Rogozhina

Evaluating the Influence of Plate Boundary Friction and Mantle Viscosity on Plate Velocities

Lithospheric plates move over the low-viscosity asthenosphere balancing several forces, which generate plate motions. We use a global 3-D lithosphere-asthenosphere model (SLIM3D) with visco-elastoplastic rheology coupled to a spectral model of mantle flow at 300 km depth to quantify the influence of intra-plate friction and asthenospheric viscosity on plate velocities. We account for the brittle-ductile deformation at plate boundaries (yield stress) using a plate boundary friction coefficient to predict the presentday plate motion and net rotation of the lithospheric plates. Previous modeling studies have suggested that small friction coefficients (l < 0:1, yield stress 100 MPa) can lead to plate tectonics in models of mantle convection. Here we show that in order to match the observed present-day plate motion and net rotation, the frictional parameter must be less than 0.05. We obtain a good fit with the magnitude and orientation of the observed plate velocities (NUVEL-1A) in a no-net-rotation (NNR) reference frame with l < 0:05 and a minimum asthenosphere viscosity of 5 1019 Pas to 10 Pas. Our estimates of net rotation (NR) of the lithosphere suggest that amplitudes 0:120:2 ( /Ma), similar to most observation-based estimates, can be obtained with asthenosphere viscosity cutoff values of 1019 Pas to 5 1019 Pas and friction coefficients