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 analog observations of Earth’s volcanic and igneous plumbing systems. Computational models help estimate those inferred magma bodies' geometry and emplacement depth. Such models have not yet simulated the dynamic fracturing of the host rocks at different gravitational accelerations on planetary bodies with different masses. We used the two-dimensional Discrete Element Method (2D DEM) to simulate the inflation of a laccolith, a magma body with a convex upward roof, in particle-based assemblages of different mechanical strengths, at the gravitational acceleration of the Moon, Mars, and Earth. The 2D DEM model simulates the host rock displacements, stresses, and dynamic fracturing, and allows calculating the finite shear strains and principal stresses. We find that in weak rocks the vertical surface displacement is nearly twice as high on the Moon, compared to Earth. Only half as many cracks are generated in strong rocks on the Moon compared to on Earth. Our 2D DEM simulations show, for the first time, that gravity specific to a rocky planetary body affects both the pattern and the amount of fracturing and surface displacement above inflating laccoliths. These findings call for a careful reevaluation of differences seen in the morphology of intrusive domes found on Earth, Mars, and the Moon.