Role of Oxygen Fugacity on the Melting Properties of Enstatite Chondrites and Implications for Mercury’s Magmatic Evolution

Mercury, the innermost terrestrial planet, is the most reduced planet in our solar system. Insights from MESSENGER mission data revealed the presence of several distinct geochemical terranes, evidence of complex magmatic processes and collisional processes exposing subsurface materials. Surface chemical analysis indicated elevated S (~2-3 wt%) and low FeO (~1.5 wt%) concentrations. The high sulfur concentration indicates reduced conditions with an average of 5.4 log units below the Iron-Wüstite (IW) oxygen fugacity (O2) buffer (IW-5.4). Surface compositions also show a range in redox conditions during mantle melting and eruption, with inferred log fO2, ranging from IW-6.5 to IW-3.5. The effects of oxygen fugacity on magmatic differentiation are poorly constrained, despite their significance in our understanding of mantle-crust differentiation in the solar system.

Enstatite High-Fe (EH) chondrites are very reduced undifferentiated meteorites with elevated concentrations of Fe and volatiles like S, Cl, Na, and K as compared to other chondrites. These characteristics suggest that EH chondrites are a potential analog for Mercury’s building blocks. However, the comparison of Mercury’s surface composition with melting products of EH chondrites is necessary to determine whether Mercury surface materials may be derived from EH chondrite- like materials. Here, we investigate the role of fO2 on EH melting properties and its implications for Mercury’s accretion and differentiation.