Dike-induced deformation and Martian graben systems

The Tharsis region of Mars is characterized by large volcanic and tectonic centers with distinct sets of graben systems. Many of the radially oriented grabens have been inferred to form in response to intrusion of magmatic dikes. This interpretation is based primarily upon early physical and numerical (boundary element) models that were developed originally to understand surface deformation associated with dike emplacement on Earth. In this study, we constructed and analyzed two-dimensional discrete element models to test the hypothesis of shallow dike emplacement and widening as a primary mechanism for the production of grabens on Mars. In particular, our models are designed to explore the extent to which a widening subsurface dike—in the absence of regional extension or pre-existing faults—will induce near-surface graben formation. The use of discrete element models allows for the permanent deformation and material heterogeneity to be captured as opposed to boundary element models that are limited by an assumption of homogeneous elastic behavior. Our analyses consider both homogeneous materials as well as mechanical stratification. The results indicate that forcible widening of a dike alone is unlikely to produce grabens at the surface. Furthermore, estimates of subsurface dike widths and emplacement depths based solely on measurements of surface graben widths may significantly over- or underestimate actual parameters. Finally, the model results suggest that the ability to distinguish between fault-induced or dike-induced graben formation mechanisms may not be possible unless the subsurface mechanical stratigraphy can be well characterized.