[Rockhounds] Remote detection of a lunar granitic batholith at Compton–Belkovich

[Kreigh Tomaszewski]

Granites are nearly absent in the Solar System outside of Earth. Achieving
granitic compositions in magmatic systems requires multi-stage melting and
fractionation, which also increases the concentration of radiogenic elements
1 <https://www.nature.com/articles/s41586-023-06183-5#ref-CR1>. Abundant
water and plate tectonics facilitate these processes on Earth, aiding in
remelting. Although these drivers are absent on the Moon, small granite
samples have been found, but details of their origin and the scale of
systems they represent are unknown2
<https://www.nature.com/articles/s41586-023-06183-5#ref-CR2>. Here we
report microwave-wavelength measurements of an anomalously hot geothermal
source that is best explained by the presence of an approximately
50-kilometre-diameter granitic system below the thorium-rich farside
feature known as Compton–Belkovich. Passive microwave radiometry is
sensitive to the integrated thermal gradient to several wavelengths depth.
The 3–37-gigahertz antenna temperatures of the Chang’e-1 and Chang’e-2
microwave instruments allow us to measure a peak heat flux of about 180
milliwatts per square metre, which is about 20 times higher than that of
the average lunar highlands3
<https://www.nature.com/articles/s41586-023-06183-5#ref-CR3>,4
<https://www.nature.com/articles/s41586-023-06183-5#ref-CR4>. The
surprising magnitude and geographic extent of this feature imply an
Earth-like, evolved granitic system larger than believed possible on the
Moon, especially outside of the Procellarum region5
<https://www.nature.com/articles/s41586-023-06183-5#ref-CR5>. Furthermore,
these methods are generalizable: similar uses of passive radiometric data
could vastly expand our knowledge of geothermal processes on the Moon and
other planetary bodies.

https://www.nature.com/articles/s41586-023-06183-5