The Compton-Belkovich Thorium Anomaly
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A few days ago Moon Zoo forum moderator Geoff posted some links to articles on lunar volcanism on the far side. Evidence of basaltic far side volcanism is already fairly well documented but this was different in that it was further evidence of silicic volcanism in a particular area of interest on the lunar far side.
Basaltic lava eruptions are generally effusive and fluid. Silicic eruptions are associated with extremely viscous lava and explosive volcanism. Non-basaltic lunar volcanism is quite rare. Examples of near side silicic volcanism have been identified in Mare Procellarum.
The Compton-Belkovich region on the northern far side (Longitude: 99.8° Latitude: 61.6°) lies between two very large ancient impact craters, Compton and Belkovich, and was found to contain large concentrations of the radioactive chemical element thorium back in 1998 when it was detected by the gamma-ray spectrometer instrument on the Lunar Prospector spacecraft. Known since as the Compton-Belkovich Thorium Anomaly (CBTA) it has remained a bit of a mystery which the Lunar Reconnaissance Orbiter is helping to unravel.
The topography of the area includes a series of domes ranging from around 1 km to 6 km in diameter, some depressions which could be evidence of collapsed volcanic features and it is also a highly reflective region. The steeply sloping sides of some of the domes are thought to have been the product of slowly flowing viscous lava. And the fact that there are few impact craters in this area indicates that, in lunar terms, this is a fairly recent fresh feature.
3D Digital Terrain Model
Follow the reference links below and the forum thread to read more about this fascinating region of the Moon.
references:
NAC image M119198897RC
42nd Lunar and Planetary Science Conference (2011)
Jules is a volunteer moderator for the Moon Zoo forum
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