GEOLOGY, GEOCHEMISTRY AND TECTONIC EVOLUTION OF THE BASEMENT COMPLEX OF GABAL EL-NUHUD AREA, SOUTH EASTERN DESERT, EGYPT
Abdel Azeim M. Mehanna
Geology Department, Faculty of Science, Benha University, Egypt.
Abstract
Gabal El-Nuhud area is occupied by schistose mafic/ultramafics and gneissic granitoids intruded by olivine gabbro-norites and various phases of dykes and volcanic plugs. Penetrative foliation and banding in amphibolites, metagabbros and gneissic granitoids, together with the mineral assemblages suggest at least two metamorphic events (M1 & M2) with peak metamorphic conditions attained in the amphibolite facies during the early deformation stages, while the retrograde greenschist facies metamorphism was coeval with the thrusting during the Pan-African orogeny.
Geochemical studies revealed that the mafic/ultramafics are enriched in incompatible elements pertaining to the P-type MORB ophiolites generated in a back-arc basin. The gneissic granitoids have calc-alkaline and I-type metaluminous characters pertaining to the volcanic arc granites and have REE characteristics consistent with subduction related magmatism.
The mafic-ultramafics represent a back-arc oceanic crust that has been intruded by subduction-related granitoids. Mylonite developed along thrusts and other tectonic boundaries that separate the different lithological domains. This area is a continuation of the Migif-Hafafit complex underwent the same evolution and tectonic deformation during the Neoproterozoic Pan-African orogeny.
Keywords: Gabal El-Nuhud, Migif-Hafafit, Geochemistry, Ophiolitic rocks, Gneissic granitoids
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