Buoyant Impact Partial Melts on Ancient Mars

Abstract

Most of the Martian crust formed prior to ∼4 Ga, but the magmatic processes responsible for finalizing the structure and composition of the ancient crust remain enigmatic. Impacts can produce large volumes of melt under a wide range of melting pressures, temperatures, and degrees of melting. Hellas, Argyre, Isidis, and Utopia basins date to around 4 Ga, demonstrating that basin-scale impacts helped to place the finishing touches on an already established crust. In this work, we focus on the ascent and intrusion of impact partial melts generated at mantle depths and the consequences for the petrology and structure of the Martian crust. Specifically, we show that the majority of impact partial melts are buoyant, favoring ascent to the surface or to neutral buoyancy levels in the crust, where magmas solidify as intrusive rocks. The composition of these polybaric melts overlaps with some ancient Martian igneous materials. We propose that the process of ascent of deep-seated impact partial melts and intrusion at shallower levels may have contributed to the observed crustal stratification and ancient petrologic diversity on Mars.