Radiogenic heat production in crustal rocks comes primarily from the decay of the naturally occurring radioactive elements uranium, thorium, and potassium, whose concentrations are highest in felsic (silica-rich) igneous rocks like granite and decrease progressively through intermediate and mafic rocks to a minimum in ultramafic rocks like peridotite, because these heat-producing elements are incompatible and preferentially concentrate in evolved, differentiated felsic melts rather than in the early-crystallizing mafic/ultramafic mineral assemblages.
Uranium, thorium, and potassium are strongly incompatible elements during igneous differentiation, meaning they are excluded from the crystal lattices of early-forming mafic minerals (like olivine...
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