AN INQUIRY INTO THE STRUCTURAL EVOLUTION OF THE NEOPROTEROZOIC SHAIT GRANITE COMPLEX, SOUTH EASTERN DESERT, EGYPT

Abstract

Geologic investigation on the basement rocks exposed around Wadi Shait revealed that they constitute part of a fold thrust nappes comprising Gardan ophiolitic mélange structural unit (GOM) exposed in a tectonic contact against the Shait granite complex (SGC). Both units are brittly to ductily deformed, and are partially intruded by the calc-alkaline Hamash granodiorite, Dokhan volcanics, post-orogenic alkali granite and the Natash volcanics. Litholgically, the GOM builds up a stack of sliced sequence comprising low-grade regionally metamorphosed epiclastic, volcanogenic pyroclastic, basic and intermediate lava flows and structurally topped by metagabbro and hornblende metagabbro slices. On the other hand, the SGC is composed mainly of mesocratic tonalite, minor leucocratic trondhjemite, granodiorite and monzogranite. The latter occurs as dyke-like masses intruding the outcrops of the other rock varieties. This lithologic association denotes that the SGC constitutes a widely evolved complex in which the early members are deep-seated, calc-alkaline and I-type whereas the later members are shallower and clearly intrusive. Field data revealed that the stacking nature and consequently uplifting of the SGC were related to late orogenic extension associated with shortening phases controlled by Najd transformed faults. Detailed field mapping and petrographic studies carried out on the Wadi Shait area show evidence of polyphase deformation (D1-D4) affecting the SGC in addition to three metamorphic events (M1,M2 and M3) affecting the GOM.