Sam Poppe , Anne Cornillon, Alexandra Morand, Claire E. Harnett

Dome-shaped, uplifted surface areas and associated fractures on Mars and the Moon are inferred to result from the shallow emplacement of magma intrusions. This inference originates from analogue observations at partially eroded or active volcanic systems on Earth. Computational models help estimating the geometry and emplacement depth of those inferred magma bodies. Models often do not consider that the gravitational acceleration is different on planetary bodies with different masses, however, and have not simulated large concentrations of magma-induced strain and dynamic fracturing of the host rocks. We used the two-dimensional Discrete Element Method (2D DEM) to simulate the inflation of a laccolith-shaped magma intrusion in particle-based assemblages of different mechanical strength, under gravitational acceleration of the Moon, Mars, and Earth. The 2D DEM model simulates the magma-induced displacements, principal stresses, and dynamic fracturing, and allows deriving shear strains in the crust. For weak rocks, the vertical surface displacement is nearly twice as high on the Moon, compared to Earth. For stronger rocks, the amount of magma-induced cracks on the Moon is half of the amount of cracks induced on Earth. Our 2D DEM simulations show, for the first time, that gravity specific to a rocky planetary body affects the pattern and amount of fracturing and surface displacement above inflating laccoliths. This calls for a careful reevaluation, and future modelling, of differences seen in the morphology of intrusive domes found on Earth, Mars and the Moon.