Effects of the Borealis impact on the mantle dynamics of Mars

Abstract

We investigate the effects of a huge impact called Borealis impact, possibly occurred at 4.5 Ga and created the northern lowland of Mars, on the thermal evolution of Mars using 2D axi-symmetric convection in a spherical shell of temperature- and pressure-dependent viscosity. A suite of models are calculated to study effects of different physical parameters on the impact-induced mantle dynamics. We use the conventional scaling laws of basin diameter and impactor size, the impact shock pressure in the interior of Mars and the foundering mechanism of impact heating to calculate the temperature increase in the mantle. The mantle is allowed to melt as its temperature surpasses the solidus. To assess the effects of the impact on the thermal evolution of Mars, we compare the thermal evolution of the models with impact to the equivalent models having no impact. It is shown that the impact increases the rate of crustal production for a period of about 50 m.y. after the impact. The initial impact-induced melt volume is about 3.44 × 10 8 km 3, whereas the impact induced mantle upwelling beneath the impact site results in the production of an extra 8.8 × 10 8 km 3 of melt. The models with no impact also produce melt in due time and the total volume of melt at 4.6 Gyr is not significantly sensitive to the impact. This observation suggests that large impacts can significantly alter the rate of crustal production of Mars but have minor effects on the total volume of crust or melt production.