Mare material originates deep in the crust

1
Formation of the Maria

• 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 KREEPy 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

2
Evolution 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 100s 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

3
MariusHills
4
Hadley rill
5
Graben and wrinkle ridges
6
Imbrium Flow fronts