Production and Preservation of Sulfide Layering in Mercury's Mantle

A striking feature of Mercury's volcanic surface is its high S and low FeO contents, which is thought to be produced by very reducing conditions compared to other terrestrial bodies. Experiments show that S solubility in silicate melts increases to % wt levels for oxygen fugacities lower than three log units below the iron-wustite (IW) buffer. During magma ocean solidification, large amounts of sulfide could potentially precipitate. This work investigates the effects of primordial sulfide layering on the first 750 Myr of Mercury's mantle dynamics. It is proposed that sulfide layering could have been produced by fractional solidification in the highly reduced Mercury magma ocean (MMO). Such chemical layering implies mantle sources with variable sulfur contents that might have played an important role in early Mercurian magmatism. Our models investigate the production of sulfide-rich layers and their preservation during post-MO solid-state mantle dynamics. An intriguing question is the role of these sulfide-rich layers on mantle dynamics as they are expected to incorporate a substantial amount of heat-producing elements (U, Th, and K). We use experimentally determined sulfur solubility in silicate melts to predict the depth at which sulfides precipitate in the MMO. The model produces primordial sulfide layers whose thickness and locations depend upon the oxygen fugacity (fO(2)) and initial sulfur content (S-init) of the MMO. Several geodynamic regimes have been identified in the fO(2)-S-init space. This study shows that oxygen fugacity, bulk sulfur content, and sulfide segregation are key for the early thermochemical evolution of Mercury.