Geology of Mairan middle dome: Its implication to silicic volcanism on the Moon

Mairan middle dome (MMD), a lunar “red spot” of silicic composition, and the surrounding maria were emplaced in the same two major episodes of volcanism. Both episodes at MMD included eruptions of low-FeO, silica-rich lava, while basaltic lava flooded the surrounding terrain during these episodes. MMD is a composite of, at least, seven small volcanic edifices. Crater counts suggest that the first episode occurred at ∼3.75 ± 0.1 Ga when low FeO, high-silica lavas erupted at MMD, and Mairan T, the small dome 11 km northwest of MMD. At about the same time, basaltic composition lava erupted southeast of MMD. A second major episode of volcanism at MMD occurred at ∼3.35 ± 0.2 Ga when low FeO, and high-silica lavas erupted at the summits of individual small volcanic edifices and a central plateau area between them. During this phase, mare basaltic lavas again flooded the area surrounding MMD and Mairan T. This sequence of events indicates that the emplacement of MMD is more complex than previously thought. In addition, the simultaneous eruption of basaltic composition lavas and low FeO, high-SiO2 lavas in this region supports the underplating model for production of magma to form the “red spots” volcanic complexes on the Moon.