Modeling of surface displacement and dynamic fracturing during magma emplacement at floor-fractured craters on the Moon and Mars

Floors of impact craters on rocky planetary bodies in our Solar System are often fractured and bulged. Such deformation features are thought to form by the ascent of impact-generated magma and the inflation of laccolith-shaped magma bodies at a shallow depth below the crater floor. Only the final surface deformation features can be observed from space, and so modeling is the only manner to understand controls on magma emplacement depth and volume, and deformation of the overlying rock. The existing models of crater floor fracturing mostly assume linearly elastic deformation of the shallow planetary crust and are not capable of simulating dynamic opening and propagation of fractures. In contrast, magma-induced deformation on Earth often displays non-elastic deformation features. This mismatch between the realistic mechanical response of planetary crust to magma intrusion and the one assumed by numerical models leads to significant inaccuracies in the modeled magma intrusion characteristics. This has important consequences for volcanic unrest monitoring on Earth and our understanding of structural deformation generated by volcanism throughout the Solar System.

We propose a new two-dimensional (2D) Discrete Element Method (DEM) approach to model dynamic fracturing and displacement in a particle-based host medium during the simulated inflation of a laccolith intrusion. The model indicates highly discontinuous deformation and dynamic fracturing and visualizes the localization of subsurface strain. We explored the effect of different gravitational conditions on the Moon, Mars and Earth on the spatial distribution of strain, stress, and fracturing above an inflating laccolith. Moreover, by systematically exploring a range of numerical parameters that govern host rock strength (bond cohesion, bond tensile strength, bond elastic modulus), and intrusion depth, we find complex controls of mechanical properties of planetary crust on the magma intrusion characteristics. Our models help understand fracture distribution patterns above laccolith intrusions in the shallow crust of rocky planetary bodies. We demonstrate that considering dynamic deformation and fracturing mechanisms in numerical models of magma-induced deformation is essential to better understand the formation of floor-fractured craters and the magmatic intrusions that lie beneath.