THERMOCHEMICAL MANTLE CONVECTION WITH FLOATING CONTINENTS, FEATURES OF THE SUPERCONTINENT CYCLE STAGES FOR TWO-DIMENSIONAL AND SPHERICAL MODELS

Abstract

We investigate the evolution of geophysical fields for spherical and Cartesian models of thermochemical mantle convection with floating continents, oceanic plates and phase transitions, with mantle heated from below and from internal  heat sources. Drifting continents remain on the surface for a long time due to increased buoyancy. In this paper we consider the stage of the supercontinent and the beginning of its disintegration. After the formation of the supercontinent, mantle flows are rearranged and a group of mantle plumes is formed under it, as well as an extended surrounding subduction zone. The hot heads of plumes located under the supercontinent increase in size due to the thermal insulating effect of the supercontinent and spread out under its lower boundary, causing tensile stresses in the supercontinent and overlithostatic compressive horizontal stresses in the subcontinental mantle. Tensile overlithostatic horizontal stresses inside the supercontinent reach 200 MPa for Cartesian two-dimensional model and up to 60–00 MPa for the spherical model, whereas overlithostatic compressive horizontal stresses in the subcontinental mantle are found under the supercontinent up to 110 MPa for the two-dimensional model and 40–80 MPa for the spherical model. Due to the lack of consideration of sphericity and the difference in the areas of the upper and lower surfaces of the mantle, two-dimensional models significantly overestimate the stresses in the upper mantle and continents compared with spherical models.