A theory of intraplate tectonics

Abstract

The theory of plate tectonics assumes a rigid behavior of tectonic plates and therefore fails to account for observed intraplate deformation. A new theory of intraplate tectonics is developed to calculate the first‐order intraplate deformation induced by horizontal displacement of deformable plate boundaries. It is based on simple assumptions that link the well‐established directions of relative plate motion to the displacement and deformation fields within a plate interior adjacent to three types of deformable plate boundaries: inward‐, outward‐, and tangential‐displaced boundaries. The theory predicts the direction of intraplate displacement, displacement rate, strain, and stress fields in terms of small circles, great circles, and 45° loxodromes around the pole of rotation of two adjacent plates. The 45° loxodromes are two orthogonal sets of directions, clockwise and counterclockwise, that intersect both small and great circles at 45°. The principal axis of the maximum horizontal stress follows small circles for inward‐displaced boundaries, great circles for out ward‐displaced boundaries, and loxodromes for tangential‐displaced boundaries. The theoretical predictions are systematically compared with more than 4000 reliable observed directions of maximum horizontal stress provided by the world stress map project [Zoback, 1992]. The theory indicates that the first‐order intraplate deformation is predominantly induced by horizontal forces acting on plate boundaries and by buoyancy forces that arise from lateral density variations between mid‐ocean ridges and plate interiors (ridge push). The simplicity of the predictions and their good agreement with observations suggests that intraplate deformation should be investigated in the pole of rotation spherical coordinate system.