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7462106 
Journal Article 
The Neoproterozoic Dubr intrusives, Central Eastern Desert, Egypt: petrological and geochemical constraints on the evolution of a mafic-felsic suite 
El-Sayed, MM 
2003 
1 
Neues Jahrbuch fuer Mineralogie. Abhandlungen
ISSN: 0077-7757 
E SCHWEIZERBARTSCHE VERLAGS 
STUTTGART 
179 
1 
1-42 
English 
WOS:000185140800001 
The Neoproterozoic magmatism in the Dubr area took place in two suites namely: (1) a mafic suite of a gabbro-diorite complex and (2) a felsic suite of a granodiorite and monzogranite composition. Pressures estimated for the gabbro and diorite rocks show that they have originated over a wide range of pressures (1.5 -6.5 kbar). The gabbro and diorite rocks predict crystallization temperatures ranging from 820 to 940 degreesC and 660 to 710 degreesC, respectively. The rare-earth element abundances of the Fe - tholeiite gabbro-diorite complex display fractionated {(La/Lu)(n) = 1.53-2.96} and LREE-enriched {(La/Sm)(n) = 1.12-2.62) patterns. The REE patterns of the gabbro-diorite complex suggest that it can be generated from a spinel-bearing mantle source. Transition metal contents of the gabbro-diorite complex are variable and low (Ni, 9-133 ppm; Cr, 20-325 ppm; Sc, 17.7-34 ppm), indicating that none of the samples are primitive. The gabbro-diorite complex may have formed via relatively high degree partial melting (25 - 30 %) of an enriched mantle source followed by fractional crystallization of olivine, Cr-spinel with minor clinopyroxene and plagioclase. Chemical evidences imply that crustal contamination is likely to be a minor factor in trace element variation of the gabbro-diorite complex. The granodiorite and monzogranite are calc-alkaline showing metaluminous affinity for the granodiorite and a slightly peraluminous nature for the monzogranite. They display trace element and REE characteristics of I-type granites formed in a subduction-related arc environment. The hornblende of the granodiorite and monzogranite yielded pressures of an average 3 kbar and 2.5 kbar, respectively. Amphibole-plagio-clase geothermometer yielded crystallization temperatures ranging from 680 to 700 degreesC and 650 to 675 T for the granodiorite and monzogranite, respectively. The co-linear trends on variation diagrams for the granodiorite and monzogranite indicate a genetic link between them through fractional crystallization. It appears likely that the restite-unmixing model is responsible for the petrological and chemical features of the grano-diorite. The most probable source for the granodiorite is a dioritic rock. The monzogranite was derived as a result of crystallization of plagioclase, biotite, hornblende, quartz, ilmenite and magnetite phases from a granodioritic melt. 
Egypt; mafic-felsic suite; thermobarometry; geochemistry; fractional crystallization; restite-unmixing