SOURCE OF LUNAR BASALT
Lunar surface basalts are believed to have their origins in partially
melted areas 100-400 kilometers (60-250 miles) beneath the large meteoroid
impact basins. The basaltic
material welled up into the basins through cracks created by
the impacts. The basalt flows covered areas up to 1200 kilometers (750
miles) away from where they had arisen.
DISTRIBUTION OF BASALT
Basalt (shown in pink) is not distributed uniformly over the Moon. Nearly
26% of the near
side of the Moon is basalt and only 2% of the far
side is basalt. Most basalt in either hemisphere is found in
areas of lowest elevation, particularly in the very large impact basins.
flows overlap each other near a wrinkle ridge in Mare Imbrium.
These lava flows are about 35 meters (115 feet) thick near their margins.
The direction of flow was from the lower left toward the upper right corner
of this photo.