Geological Atlas of Africa
Geological Atlas of Africa
Egypt (p. 88-89)
1 General Area: 997,739 km²
Population: 65,700,000 (Estimate 2001)
2 Summary of Geology
The oldest rocks in Egypt occur as isolated Archean to Proterozoic inliers in the Western Desert, whereas the Egyptian part of the Arabian-Nubian Shield along the coastal Red Sea region is made up of Neoproterozoic Pan-African rocks. Paleozoic sediments often mantle the basement rocks. After a sedimentary hiatus due to the Hercynian orogeny Cretaceous sediments are well exposed in various parts of the country. The Cenozoic history is characterized by transgressions and regressions and their respective sediment types.
3 Stratigraphy and Tectonics
Much of northeastern Africa is mantled by thick sedimentary strata of Phanerozoic age, which form a generally undeformed cover to a deep crystalline basement. The older rocks are well exposed in eastern Egypt and Sudan, where they comprise part of the Arabian-Nubian Shield. Further into the interior of northeastern Africa they appear as isolated inliers, for instance the Uweinat inlier across the borders of Egypt, Libya and Sudan. The Uweinat inlier is also significant because it has provided the oldest ages from anywhere in northeast Africa: Granulite facies rocks in this area have yielded an average age of about 2,900Ma. No younger ages than about 1,800Ma have been obtained there, thus indicating the tectonic stability of the Uweinat inlier since that time. It is therefore probable that this region is to be considered part of a craton from thence on.
Till to date, no pre-Pan-African rocks have been identified in other regions of Egypt. The basement rocks in the Eastern Desert of Egypt can be subdivided from base to top into the Meatiq Group, the Abu Ziran Group and the Hammamat Group, all of Neoproterozoic age. The Meatiq Group comprises old crystalline basement outcropping in gneiss domes. These probably evolved in a mainly compressional tectonic environment during Neoproterozoic times and exhibit many of the basic structural and lithological characteristics of metamorphic core complexes of the Cordilleran type. They comprise an anticline with low dipping foliation and unidirectional mineralslickenside lineation. The core comprises granitic gneisses conformably overlain by a heterogeneous and isoclinically folded mylonitic material, which predates the doming event. This grades up into low-grade ophiolitic rocks.
The area lies in the foreland fold and thrust belt of a continental margin origin. Ophiolites outcrop along the thrust between the Meatiq infrastructure and the imbricated Abu Ziran nappe. Calc-alkaline magmatism occurred along two upwards and is associated with gold mineralization. The Abu Ziran Group comprises ophiolites overlain by metasediments, pyroclastics and local intermediate volcanics with island arc characteristics. The Hammamat Group includes molasse-type clastics and the penecoeval Dokhan volcanics of andesitic to rhyolitic composition, these being equivalent to plutonic, syn- to late-tectonic calc-alkaline granites.
The clastics are up to 5,000m thick, of Late Pan-African age and exposed in the coastel mountains of the Eastern Desert. There are four lithofacies, which are conglomerate, pebbly sandstone, sandstone and siltstone, respectively. The interrelationships suggest alluvial fan-braided stream deposition within several small-sized basins. The interbedding of conglomerate and thick siltstone units indicate the direct interdigitating of fans with playas or lake sediments. Discontinuous siltstone units are interpreted as cut-off channel deposits within braided streams. Debris flow sedimentation is not exhibited. Palaeomagnetic directions have been identified at several sites in the Dokhan volcanics and also from two dike swarms intruding the late orogenic (younger) granites.