Numerical modeling of the distribution of horizontal stresses in a moving continental plate

The distribution and time evolution of overlithostatic horizontal stresses in the vertical cross-sections of the model of a solid continent are studied in terms of a 2D numerical model. The continent is moving self-consistently with time-varying mantle flows. Over a period of 50 Ma, the continent, which had been initially located at a distance of about 1500 km from the downward mantle flow (subduction zone), first overlays the region of the marginal sea, then thrusts over the zone of subduction, thus making it inclined and deforming it. It is found that the horizontal tensile stresses observed at the initial stages are succeeded by compressive stresses, especially at the leading edge (up to 40 MPa). This is caused by the change of the dragging action of the subduction zone into the retarding action during the continent crossing over this zone. The dependence of the calculated stresses on the Rayleigh number and on the thickness of the model of the continent is estimated. It is obtained also that the distribution of horizontal stresses along the strike of the continent is rather distinctly indicative of the locations of upward and downward flows in the subcontinental mantle. With the considered values of the model parameters, the tensile stresses in the near-to central regions of the continent may be twice to thrice the tensile stresses at its margins. Hence, in the simplest case of a homogeneous continent, its division will occur in the zone directly above the upward subcontinental flow. Detachment from the continent of the fragments of its edge adjacent to the marginal sea implies that the thickness of the continental plate in that part and/or its strength is considerably lower than in the center of the continent.