Crustal remelting origin of highly silicic magmatism on the Moon

Orbital observations of non-mare, highly silicic volcanic constructs on the Moon challenge the conventional view of the formation of silicic crusts in the presence of water and plate tectonics—the former the Moon has in very short supply and the latter it likely never ever had. Revealing the silica-rich magma origin may reshape our understanding of early planetary crust formation. However, the cause of lunar silicic magmatism remains enigmatic. Here we conduct phase equilibrium simulations for potential lunar igneous lithologies that demonstrate that the compositions of silicic volcanic constructs can be produced by partial melting of KREEP (potassium, rare earth elements, and phosphorus) basalts. Either internal radiogenic heating or external impact bombardment can provide the heat needed for KREEP basalt melting. Combined with silica-rich materials identified on other rocky planets, we suggest that highly evolved crusts might be more prevalent in the early solar system than anticipated as they can originate from crustal remelting in the absence of water and plate tectonics.