Investigations into Mercury's mantle through the partial melting of Enstatite (EH) Chondrites

The mantle and surface of Mercury exhibit distinct characteristics that set it apart from other terrestrial bodies, largely due to its extremely low oxygen fugacity (fO₂). This reduced state has resulted in unique compositional features, such as the planet's depletion in FeO and enrichment in volatile elements (e.g., Na, K, S). These properties present a challenge in understanding terrestrial differentiation processes on Mercury. To investigate these features, I conducted high-pressure, high-temperature partial melting experiments on enstatite chondrite (EH) compositions, simulating Mercury-like conditions. These experimental results were paired with thermodynamic modeling (using pMELTS) to capture the effects of varying fO₂ on Mercury's mantle compositions and melting behaviors. This study's findings were compared to MESSENGER mission surface composition data to assess the feasibility of EH chondrites as Mercury's primary building blocks. This study demonstrates that fO₂ could be a key factor influencing Mercury's mantle melting behavior and surface composition. At lower fO₂ conditions, silicon preferentially partitions into the metallic phase, resulting in silicate melts with elevated Mg/Si, Ca/Si and Al/Si ratios. Thermodynamic modeling enabled us to estimate partial melt compositions at 1 GPa and 1300-1650 degreesC between the silicate solidus and liquidus. These resulting melt compositions closely align with the geochemical signatures observed on Mercury's surface, as reported by MESSENGER. Silicate melt compositions range from picro-basalt to phonolite, highlighting how the reduced conditions of Mercury's mantle are a key factor in generating its surface geochemical diversity. Variations in mantle fO₂ can drive complex magmatic differentiation and volcanic evolution in reduced planetary systems.