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Umm Anab granitic pluton has an inhomogeneous composition which varies from quartz-monzodiorite, granodiorite to monzogranite. The former two varieties have strong trondhjemitic affinities. Similar to most trondhjemites, they display high soda, low potash and lime, comparable FeO*, MgO, FeO/MgO and K2O/Na2O and are commonly corundum normative. The complete monzodiorite, granodiorite, monzogranite suite exhabits calc-alkaline fractionation trend with some transitional trondhjemitic tendencies. These geochemical aspects characterize the Proterozoic active continental margins, that apparently related to subduction.

The REE geochemical characteristics of Umm Anab granitoids are interpreted to have been produced by partial melting of amphibolite, leaving residues consisting mainly of hornblende.

Many lines of evidence suggest that Umm Anab granitoids are interrelated by crystal fractionation. Albite and antiperthite fractionation can explain some of the scatter in the trondhjemitic varieties which has been noticed within many trondhjemitic suites and was interpreted as a primary magmatic feature.