UC Berkeley

The ancient crust of Mars contains a remarkable record of the planet's early history. With 45% of the martian crust dated to the Noachian (>3.7 Ga) and another 30% of the crust dated to the Hesperian (>3 Ga), Mars provides a unique opportunity to examine processes that can influence the early evolution of terrestrial planets. Observations of Mars' surface motivate hypotheses as to what processes controlled the planet's early evolution and how the surface developed into its present form. Key features to explain for early Mars are the formation of the crustal dichotomy, the massive Tharsis volcanic province, and the prevalence of features indicating widespread early water. Hypotheses for the formation of these features can be tested using geodynamic models. For the origin of the crustal dichotomy, both endogenic (mantle convection) and exogenic (giant impact) mechanisms have been proposed. We examine if a hybrid model in which a giant impact can influence the global pattern of mantle convection. We find that a superplume can form on Mars following an early giant impact, and examine the subsequent superplume dynamics and migration in relation to the formation of Tharsis and remanent crustal magnetism. For a purely giant impact origin of the crustal dichotomy, we find that the crustal structure of the dichotomy is difficult to reproduce with high-resolution impact models. We also examine evidence for early oceans on Mars, finding that deviations in proposed paleoshoreline elevations from present-day equipotential surfaces can be explained by deformation due to the emplacement of Tharsis and other surface loads. Our results suggest that Mars paleoshorelines follow paleo-equipotentials, supporting the ocean hypothesis. Overall, our results provide insight into the early processes that may have occurred on Mars, and their effect on the subsequent evolution of the planet.