The role of assimilation and fractional crystallization in the evolution of the Mars crust

Abstract

Recent findings of evolved martian crustal materials by orbiters and rovers challenged the longstanding notion of an only-tholeiitic basaltic crust. Models exploring intraplate magmatic processes like fractional crystallization show that unrealistic amounts of solid accumulation are sometimes required for the formation of martian evolved materials, including evolved materials analyzed by the Curiosity rover at Gale crater. Assimilation and fractional crystallization (AFC) play an important role in the diversification of magmas on Earth, but has not been explored for its role in the generation of evolved martian compositions. In this study, we conduct a series of thermodynamic AFC models using the Magma Chamber Simulator (MCS) model interfacing with the Rhyolite-MELTS algorithm to better understand the controls on assimilation and whether it contributed to the evolution of the martian crust. We find that AFC models replicate evolved Gale crater targets effectively at different pressures and water contents. AFC likely contributed to martian crustal formation, particularly evolved compositions. Higher crustal temperatures likely lead to a higher volume of evolved magmas formed by AFC processes on early (rather than modern) Mars. AFC may have also occurred during the Amazonian, especially in the fractured upper layers of crust, although in lower volume than during the Noachian.