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Neoproterozoic rocks in the Umm Gheig Province (UGP), central Eastern Desert, comprise five plutonic rock-suites, i.e. a gabbro-diorite suite (GDS), an older granitoid suite (OGS), an I-type younger granitoid suite (1-YGS), an A-type younger granitoid suite (A-YGS) and a garnet-bearing granitoid suite (GBGS). The GDS exhibits a tholeiitic affinity generated in a volcanic arc, subduction-related environment. The unfractionated REE pattern of the gabbro {(La/Lu)(N) = 0.6} differs significantly from the fractionated pattern of the diorite {(La/Lu)(N) = 5.07}. They are, however, characterized by flat HREE {(Gd/Lu)(N) = 1.24 and 1.45, respectively} and the absence of a Eu anomaly (Eu/Eu* = 1.03 for both). The rocks of the GDS do not represent a primary magma, and the gabbro could be generated by high degree melting of a garnet-free source followed by crystallization of clinopyroxene and olivine. The dioritic melt could be produced by melting of gabbroic, rocks.

The granitoids can be divided into four general suites emplaced late- (OGS, I-YGS and GBGS) and post-tectonically (A-YGS), each of which shows some variations in their bulk chemical compositions. All the granitoid suites display ferriferous and metaluminous affinities and belong to the non-alkaline series: OGS and I-YGS represent calc-alkaline magmatism while A-YGS and GBGS encompasses highly fractionated calc-alkaline magmatism. There is substantial uniformity in REE patterns between the OGS, I-YGS and A-YGS, with no real change in light to heavy REE ratios. Chondrite-normalized REE patterns of the GBGS is characterized by strong enrichment in HREE and pronounced negative Eu anomalies (Eu/Eu* = 0.095) compared to the other granitoid suites. The geochemistry and petrological characteristics of the granitoid suites suggest close genetic relationships and it is suggested that they were formed from a single parent magma, over a relatively short period of time. Major and trace element variations in the different granitoid suites indicate that they can be modelled by fractional crystallization of plagioclase, K-feldspar, biotite and hornblende. Variation in REE patterns are governed by fractionation of accessory phases such as apatite, monazite and zircon which occur as inclusions in phenocryst phases.