The volcanotectonic evolution of Mare Frigoris

The basalt fill within Mare Frigoris is thick (greater than 400 m) and was emplaced in at least three major episodes within topographic lows overlying a thick lunar lithosphere. The oldest identifiable unit is dominated by titanium-poor lavas and was succeeded by basalts of intermediate and titanium-rich composition. The lavas appear to have been emplaced largely by flood-style eruptions. The topographic low of western Frigoris was probably created by the collapse of highland blocks into the Imbrium impacta cavity. The line of separation may have been an Imbrium ring fracture or a ring fracture of the older Procellarum basin.