Basalt - Lunar and Martian Basalt

Lunar and Martian Basalt

The dark areas visible on Earth's moon, the lunar maria, are plains of flood basaltic lava flows. These rocks were sampled by the manned American Apollo program, the robotic Russian Luna program, and are represented among the lunar meteorites.

Lunar basalts differ from their terrestrial counterparts principally in their high iron contents, which typically range from about 17 to 22 wt% FeO. They also possess a stunning range of titanium concentrations (present in the mineral ilmenite), ranging from less than 1 wt% TiO₂, to about 13 wt.%. Traditionally, lunar basalts have been classified according to their titanium content, with classes being named high-Ti, low-Ti, and very-low-Ti. Nevertheless, global geochemical maps of titanium obtained from the Clementine mission demonstrate that the lunar maria possesses a continuum of titanium concentrations, and that the highest concentrations are the least abundant.

Lunar basalts show exotic textures and mineralogy, particularly shock metamorphism, lack of the oxidation typical of terrestrial basalts, and a complete lack of hydration. While most of the Moon's basalts erupted between about 3 and 3.5 billion years ago, the oldest samples are 4.2 billion years old, and the youngest flows, based on the age dating method of "crater counting," are estimated to have erupted only 1.2 billion years ago.

Basalt is also a common rock on the surface of Mars, as determined by data sent back from the planet's surface and by Martian meteorites.