A 3-D NUMERICAL MODEL OF THE WILSON CYCLE

Abstract

Three-dimensional (3-D) numerical modelling in a rectangular box is provided for the evolution of mantle structure induced by two floating continents. As initial state we take quasi-steady state mantle convection with many Benard cells. Then we place two continents (with figures similar to Lauorasia and Gondwana) near and on opposite sides of central downwelling mantle current. Our model shows the aggregation of continents and their dispersal. This resembles the history of the Pangaea supercontinent. We solve the system of hydrodynamical equations for a viscous mantle (heated from below and inside) and Euler's solid-body equations for continents. Due to mantle drag forces the floating continents drift towards the nearest downwelling and form a single supercontinent like Pangaea. The mantle under the supercontinent becomes warmer and new upwelling appears. This drags the continents away and produces an ocean with a long mid-ocean ridge. One part of this ocean is similar to the present Atlantic without subduction zones. The other part is similar to the Pacific. In the Pacific region the mantle current steeply descends under the first continent and gently under the second continent. The global heat flow distribution is similar to the observed heat flow with local maxima in the position of marginal basins. The principal results of the numerical modelling are: (a) the global geodynamic evolution of the Earth strongly depends on the thermal interaction between moving continents and mantle convection; (b) continents try to cover downwelling, then this downwelling disappears or moves sideways. The belts of subduction zones appear after break-up of the supercontinent near the margins of the continents. Some of these subduction zones could be relics of paleo-downwellings; (c) new upwelling appears under the continent and increases mantle heat flow. Part of this flow exits through the continental margin near the subduction zone and produces marginal basins.