Does shallow dike intrusion and widening remain a possible mechanism for graben formation on Mars?

Abstract

Shallow dike intrusion and widening was proposed several decades ago as a cause of surface faulting and graben formation on Earth. This hypothesis was subsequently applied to the spectacular linear and/or radial graben systems visible on Mars. However, a recent study has suggested that shallow dike intrusion on Mars results in contractional folding and uplift adjacent to dike walls rather than extensional faulting and subsidence above the dike tip, even in the presence of concurrent regional extension. Here, discrete element numerical modeling is used to re-examine the typical style of deformation above the shallow tips of widening dikes on Mars. The dikes are embedded in a frictional, cohesive material representing the Martian crust. In the experiments presented here, subsidence and extensional faulting (graben formation) are produced above the dike tips, even with modest amounts of widening. For suggested depths to dike tips on Mars, an overlying graben is produced in all cases; no upright detachment-style folds are produced. Results indicate that dike widening does indeed remain a possible mechanism for graben formation on Mars. Implications for the interpretation of deformation associated with shallow dike intrusion on Earth and distant planetary surfaces are discussed.