Heterogeneity and time dependence in 3D spherical mantle convection models with continental drift

Feedback between continents and large-scale mantle flow through thermal blanketing has long been surmised as a mechanism for continental drift and Wilson cycles. Paleomagnetism provides evidence for extensive continental displacements (similar to 10,000 km) on time scales of 100-200 million years, comparable to an intrinsic overturn in whole mantle convection. Here we model continental motions in vigorous 3D spherical convection models, focusing on the effects of continent size, mantle heating mode, and a strong increase in lower mantle viscosity. Continents covering 30%, 10%, and 3% of Earth's surface (representative of the former supercontinent Pangea, present-day Asia, and Antarctica, respectively) are introduced into simple end member mantle convection models characterized by pure core or internal heating, and uniform or layered mantle viscosity. Supercontinents promote temperature anomalies on the largest scales (spherical harmonic degrees 1 and 2), primarily through the organization of the long-wavelength convective planform inherent in models with a high-viscosity lower mantle. Bottom heating can promote long-wavelength heterogeneity by clustering plumes beneath the continent. However, in isoviscous models small-scale structure persists away from the continent regardless of the heating mode. Supercontinents respond to long-wavelength heterogeneity by following great circle paths with variations in velocity on time scales of 1 billion years. Smaller continents are unable to promote long-wavelength structure, and the resulting motions are governed by bursts in velocity on time scales of the order of 100 million years. Continental velocities are roughly a factor of similar to 3 smaller than those in oceanic regions, an observation that may help explain the observed difference in the speed of predominantly continental or oceanic plates. (c) 2005 Elsevier B.V. All rights reserved.