Impact megadomes and the origin of the martian crustal dichotomy

We show that a sufficiently energetic impact can generate a melt volume which, after isostatic adjustment and differentiation, forms a spherical cap of crust with underlying depleted mantle. Depending on impact energy and initial crustal thickness, a basin may be retained or impact induced crust may be topographically elevated. Retention of a martian lowland scale impact basin at impact energies ∼3×10²⁸-3×10²⁹J requires an initial crustal thickness greater than 10km. Formation of impact induced crust with size comparable to the martian highlands requires a larger impact energy, ∼1-3×10³⁰J, and initial crustal thickness <20km. Furthermore, we show that the boundary of impact induced crust can be elliptical due to a spatially asymmetric impact melt volume caused by an oblique impact. We suggest the term " impact megadome" for topographically elevated, impact induced crust and propose that processes involved in megadome formation may play an important role in the origin of the martian crustal dichotomy.