Russian Journal of Earth Sciences
Vol. 3, No. 2, May 2001

A numerical evolutionary model of interacting continents floating on a spherical Earth

V. P. Trubitsyn and V. V. Rykov

Abstract

Development of methods for the numerical modelling of global geodynamic processes provided a possibility to study the driving mechanism of moving continents periodically assembling to form supercontinents of the Pangea type. In our previous studies, we developed a method for the numerical solution of a system of equations governing the mass, heat and momentum transfer in a convecting viscous mantle and Euler equations describing the motion of solid continents. The convection and Euler equations are coupled through the conditions of no-slip, impermeability and continuity of temperature and heat flux at the continent surface submerged into the mantle. These studies demonstrated the capability of continents to assemble into a supercontinent and the capability of a supercontinent to break up. Based on an idealized spherical model, this work presents results of a numerical experiment with long evolution of 12 floating continents. The mantle was modelled by a spherical shell of a constant viscosity heated from below with the Rayleigh number Ra = 107. The continents were represented by thick rigid discs with angular dimensions of about 40o times 40o. The initial state was modeled by the present mantle with a temperature distribution estimated from seismic tomography data. In this state, the distributions of the surface heat flux and mantle flow velocities are consistent with observations. The continents in the initial state are uniformly distributed over the mantle surface. The long-term evolution of the mantle-continents system, lasting a few billions of years, was calculated. A numerical experiment conducted within the framework of this idealized model showed that, for the most time, the continents are located above mantle downwellings and move together with them. If two mantle flows accidentally approach one another, a zone arises that pulls adjacent continents in (along with underlying mantle flows). As a result, mantle downwellings and the related continents start joining. Our numerical experiment showed that the continents first form groups of four to five continents and a large supercontinent is then assembled from these groups. The overheated mantle under the supercontinent gives rise to new convective upwellings. As a result, the supercontinent first divides into two smaller supercontinents. Afterward, the latter also break up. One of the smaller supercontinents (similar to Laurasia) first breaks up into five continents, after which the second supercontinent (similar to Gondwana) also divides. Afterward, the continents scatter all over the mantle surface. The convergence and divergence events repeatedly occur during the evolution.