the compton-belkovich thorium anomaly features concentrations up to 5.3 ppm at its center, far exceeding the surrounding lunar highlands' typical 0-2 ppm and indicating ancient volcanic activity.
this is lower than earth's continental crust average of 9.6 ppm but represents a unique hotspot on the moon.
wikipedia.
washington university.
Compton–Belkovich Thorium Anomaly - Wikipedia
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