What controls chemical variation in granitic magmas?

► Most models for chemical variation in granites are inadequate to account for the main variations. ► Many processes can play secondary roles but peritectic assemblage entrainment dominates. ► Partial melt may segregate from its residue carrying crystals of the peritectic assemblage. ► Peritectic crystals are entrained in a ratio decreed by the stoichiometry of the melting reaction. ► Thus, protolith composition is the primary control on granite magma chemistry.