• 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 (3.8-3.1 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

Edges of the Maria remain sharp Little lateral mixing from impacts

Evolution of the Maria

MariusHills

Hadley rill

Graben and wrinkle ridges

Imbrium Flow fronts