GEOLOGY AND GEOCHEMISTRY OF THE BASEMENT ROCKS IN GABAL RIBDAB - GABAL SHASHOBA AREA, SOUTH EASTERN DESERT, EGYPT

Abstract

The evolution of the Arabian - Nubian Shield in the light of the plate tectonic concept involved multicyclic island arcs (forearc), with continuos deformation and ophiolitic obduction occm/ing primarily during phases of arc .,..._ collision, however the ultimate result of these processes was the progressive cratonization of a large volume of new crust (Greenwood et. al.l976; Gass, 1977, 1981). Another mode suggests the Precambrian continental crust of Egypt and western Saudi Arabia is evolved in the same way to the Indian type orogeny in its broad sense (Nawab, 1978).

The Precambrian rocks of Egypt (100, 000 Km2) outcrop over an extensive area in the Eastern Desert, southwestern part of the Western Desert and south Sainai. The Precambrian belt represents the NE part of the Arabian -Nubian Shield which is exposed in both sides of the Red Sea, and belonging to the Pan- African orogenic belt.

The Egyptian Precambrian belt of the Eastern Desert is composed of an upper - Proterozoic volcano - sedimentary complex containing scattered ultramafic mafic bodies and intruded by syn- to late- tectonic plutonites (mainly tonalite to granodiorite) with extrusive series of calc- alkaline volcanic rocks. This sequence • is unconformably overlain by molasse sediments of the Hammamat group. The sequences are cut by alkaline to sub alkaline late- to post- tectonic granites.