Mare material originates deep in the crust – Maria lava fill pre-existing depressions (impact basins) – High levels of pyroxene and olivine relative to the upper crust – Very similar to terrestrial basalt Except that it is completely devolatilized Also abnormally high in titanium – Darker color due to higher Fe content Amounts are small… – Most Maria 1-2km thick – 5km in Imbrium, 0.6km in Orientale – Individual flows ~10-40m thick – VERY low viscosity Some maria material interacts chemically with the KREEP layer as it rises – Known as KREEP’y maria Maria erupt mostly during the Imbrian period ( Ga) A little late Mare formation into the Eratosthenian period but not much Formation of the Maria

Maria lava fill pre-existing depressions (impact basins) Maria does not reach surface on the far-side due to the thicker crust. Cryptomaria – some maria can be buried Very smooth on scales of 100’s of meters Weight of maria material causes subsidence – Compression (wrinkle ridges) in the center – Extension (graben) at the edges l Edges of the Maria remain sharp n Little lateral mixing from impacts Evolution of the Maria

Marius Hills

Hadley rill

Graben and wrinkle ridges

Imbrium Flow fronts