3-D Spherical Models of Mantle Convection: A Study of the Impact of Tectonic Plates, Nuvel 1 Plate Motions and Seismic Tomography

We explore here the influence of realistic characteristics of mantle convection such as tectonic plates, the surface velocity field from the Nuvel-1 No-net-rotation (NNR-1) model (Argus & Gordon, 1991), and the 3-D mantle structure described by global seismic tomographic reconstructions (Grand, 2002). We first established a `reference' 3-D spherical convection model which incorporates surface plates in a dynamically self-consistent way (Monnereau & Quéré, 2001). This reference model, with a simple two-layer viscosity profile, reproduces the main features of plate tectonics: linear subduction zones and spreading along mid-ocean ridges and deep-seated hotspot plumes (numbering three in this model) which extend to the surface. The next level of modelling involved taking the average radial temperature field from the reference model and imposing the velocity field from NNR-1 in a time-dependent thermal convection simulation. This second convection model is distinctly different from the reference model because the balance of flow-induced torques acting on the plates (e.g., Ricard & Vigny, 1989) is no longer verified. We now observe as many as six hotspot plumes, close to the number of principal or major hotspots which have been identified for the Earth (Courtillot et al., 2004). In a final series of convection simulations, the 3-D mantle structure from seismic tomography is employed as a starting condition. We now observe another distinct manifestation of evolving hotspot plumes in the mantle. We will also report here on the implications of these models for global heat flow at the surface and at the core-mantle boundary.