A 3-D NUMERICAL-MODEL OF THE WILSON CYCLE

Three-dimensional (3-D) numerical modelling in a rectangular box is pr ovided for the evolution of mantle structure induced by two floating c ontinents. As initial state we take quasisteady state mantle convectio n with many Benard cells. Then we place two continents (with figures s imilar to Lauorasia and Gondwana) near and on opposite sides of centra l downwelling mantle current. Our model shows the aggregation of conti nents and their dispersal. This resembles the history of the Pangaea s upercontinent. We solve the system of hydrodynamical equations for a v iscous mantle (heated from below and inside) and Euler's solid-body eq uations for continents. Due to mantle drag forces the floating contine nts drift towards the nearest downwelling and form a single superconti nent 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 midocean ridge. One part of this ocean is simila r to the present Atlantic without subduction zones. The other part is similar to the Pacific. In the Pacific region the mantle current steep ly descends under the first continent and gently under the second cont inent. The global heat flow distribution is similar to the observed he at flow with local maxima in the position of marginal basins. The prin cipal results of the numerical modelling are: (a) the global geodynami c evolution of the Earth strongly depends on the thermal interaction b etween 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 superconti nent near the margins of the continents. Some of these subduction zone s could be relies of paleo-downwellings; (c) new upwelling appears und er the continent and increases mantle heat flow. Part of this flow exi ts through the continental margin near the subduction zone and produce s marginal basins.