Magma chamber longevity on Mars and its controls on crustal structure and composition

Abstract

In volcanically active planetary bodies, the depths and longevity of crustal magma storage critically control eruptibility and crustal composition. A paucity of relevant observations and models has challenged our understanding of the development of crustal magma storage systems in Mars and their role in the apparent lack of evolved compositions. Here, we use numerical modelling, together with recent results from the InSight mission, to study the evolution of crustal magma chambers on Mars and conditions that promote their growth and eruptibility. We find that the Martian crust can be divided, by depth, into three major domains. For Elysium Planitia (the InSight landing site), at depths ≤15km (~1.5kbar), trapped magma pods are small, short-lived, with high diking potential, hindering the production of evolved compositions. While depths >25km (~2.5kbar) can host long-lived magma chambers, 15-25km (~2 ± 0.5kbar) marks a transition where magma chambers could grow while concurrently expelling magma. Interestingly, this narrow depth window overlaps with the depth of an intra-crustal discontinuity reported by InSight, suggesting a possible magmatic origin for the discontinuity. We further show that the crustal thermal gradient strongly controls this transition depth, indicating the possible variability of the domain depths in different terrains. Our results also support the likelihood of deep-seated magmatism beneath the seismically active Cerberus Fossae, suggesting that magmatism continues to play a major role in shaping the Martian crust.