A-type granites are characterized by highly evolved composition, enrichment in high field strength elements (HFSE), varied alkalinity and alumina saturation state and dominance of ferroan affinity. A-type granites are sourced from either crust or mantle rocks or both, in an extensional setting.
S-type granites formed by partial melting of sedimentary rocks in thicken crust due to collision are mostly calcalkaline, strongly peraluminous and ferroan, with relatively less abundant HFSEs.
A type granites generally formed from a highly evolved mafic alkaline mantle melt (however, some of them may related with mestasomatized crustal material). Also A type granites have tendecies to host economic grades of incompatible elements including REE, Th, U, Nb, Ta etc.
S type granites are mostly related with a continental collision process with partial melting and fractionation. Also they can host high grades of U, Nb,Ta,Th,Zr, Ga and HREE.