Three-dimensional modelling of dike-induced graben formation

Graben formation above pressurised dikes is simulated using a novel damage model for compressive shear failure implemented in the commercial finite element software COMSOL Multiphysics. The damage model allows fractures to form and propagate naturally. No remeshing is required and it is sufficiently computationally efficient to be implemented in three-dimensions. It is shown that grabens can readily form above dikes under realistic magmatic overpressures, and that this stress relief mechanism can halt the vertical ascent of dikes, encouraging lateral propagation of the dike and the graben above it. The faults that form the graben are found to initiate at the upper tip of the dike and then grow towards the surface. Once initiated, the graben is shown to form ahead of a laterally extending dike. A number of factors are investigated: the effect of dike-depth, the cohesive strength and friction angle of the overlying rocks; the influence of symmetry breaking on the formation of half-grabens; and the difference between graben formation on Earth and Mars which is manifest in the change in gravity. The latter is used to interpret recent observations of the giant graben system in Elysium Fossae on Mars by Rivas-Dorado, Ruiz and Romeo, JGR: Planets, 126 (2021).