Tectono-topographic response of convergent plate margins to changes in submarine margin relief – a combined analysis using analytical and numerical force-balance models

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The subduction of oceanic lithosphere at convergent plate margins leads to deformation and mountain building, which over millions of years results in an equilibrium between the shear force along the plate boundary and gravitational forces. The shear force causes compression in the upper plate and drives deformation and orogeny. In contrast, the margin relief, i.e. the difference in elevation between the trench and the highest topography in the upper plate, causes a gravitational pressure gradient that creates deviatoric tension and counteracts the compression. When the shear and gravitational forces are in balance, the stresses in the upper plate are minimized. A disturbance in the force balance, however, alters the stresses in the upper plate and drives deformation and topographic adjustments until the stresses are minimized again. The planned project will investigate how disturbances in force balance due to a) the subduction of a submarine ridge and b) the transition from subduction to continental collision affect the tectono-topographic development of the upper plate. In both cases, the depth of the trench and therefore the submarine relief decreases, which alters the balance between gravitational and shear forces and promotes deformation and mountain building. To investigate the effect of a submarine margin-relief reduction on the stress field and topography of the upper plate, we will combine analytical force-balance calculations with 2D and 3D finite element modelling. The project includes a detailed parameter study to identify the main factors that determine the response of the upper plate to perturbations in force balance. The parameters considered include, among others, the absolute relief change, the dip angle of the oceanic plate as well as the mechanical strength of the plate boundary and upper plate. By using 3D finite-element models, margin-parallel stresses and deformation patterns arising from oblique subduction will, for the first time, be taken into account when evaluating the force-balance changes. We will apply our models to natural case studies, including the Cocos Ridge (Central America), the Nazca Ridge (Peru) and the incipient collision at the Sunda-Banda arc (Southeast Asia). The novel combination of analytical and numerical force-balance models will yield detailed and quantitative constraints on how changes in submarine margin relief due to the subduction of a ridge or a passive continental margin affect the stress field and topography in the upper plate. The results will be relevant for investigating stress and deformation patterns at active and fossil continental margins as well as for reconstructions of palaeotopography. Ultimately, the project will contribute to significantly improve the understanding of the effects of relief changes on the tectono-topographic evolution of convergent plate margins.