A Craton is an ancient piece of earth’s continental crust, one that has been stable for billions of years.
The Earth naturally contains elements that give off heat, such as radioactive potassium, thorium, and uranium. When the mantle melts, those elements move into the melt, extracting them from the mantle and moving them upward. Once those elements are concentrated in the crust, the heat can rapidly escape out into space. Once that heat is removed, the crust can become cold and stable, hard to deform.