Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques…

Neoproterozoic crust, now widely exposed in parts of Egypt, Saudi Arabia, Sudan, Eritrea, Ethiopia, Yemen, and Somalia. The ANS was formed during the Neoproterozoic between 900 and 550 Ma through the accretion of intra-oceanic arcs during the closure of the Mozambique Ocean and the amalgamation of Gondwana [2]. These accretion processes led to the formation of well-defined arc-arc and continent-arc suture zones [3, 4]. The ANS was essentially stable continental crust by Early Cambrian time at 530 Ma [5]. The ANS and its surroundings has been the object of geologic investigations for a wide range of geological economic and scientific reasons.

The Precambrian basement of the Eastern Desert of Egypt (ED) is a part of the Arabian-Nubian Shield (ANS) and are exposed mainly in the Eastern Desert and Sinai (Figure 1). The Eastern Desert of Egypt comprises variably deformed and metamorphosed volcanic, plutonic, and sedimentary rocks of Precambrian age, unconformably overlain by Cretaceous sediments. The Eastern Desert of Egypt is classified into three domains: north, central, and south [6], all revealing different aspects of the region's protracted and intense Neoproterozoic episode of deformation and igneous activity. The Central Eastern Desert (CED) preserves the oldest (Tonian-Cryogenian) history and also best preserves Ediacaran deformation as well as associated (Hammamat) basins. The Southern Eastern Desert (SED) lacks BIF, Ediacaran sedimentary or volcanic successions such as the Hammamat Group and Dokhan Volcanics, whereas the CED does not [7]. The Northern Eastern Desert (NED) is very different than either the CED or the SED. Dokhan volcanics and Hammamat molasses sediments are of widespread occurrence, whereas ophiolites are absent and gneisses are rare.

Geochemistry and Tectonic Setting of Neoproterozoic Rocks from the Arabian-Nubian Shield…

DOI: http://dx.doi.org/10.5772/intechopen.82519

The reconstructions of this chapter are based on a compiled data of geochemistry and obtained ages on the rock units constituting the Eastern Desert of Egypt. Geochemical data are based on combination of major elements, trace elements, rare earth element (REE) distributions as well as isotope data. In this contribution, I build on previous geological and geochemical studies on the different rock units forming the ED for many years of research to summarize the most important geochemical characteristics of the different rock units and to provide some important information regarding the geochemical dynamic and evolution of Neoproterozoic crust of the ED. This chapter reviews the scope of current geochemical and isotopic datasets for the ANS, with particular emphasis on the

The Precambrian basement rocks of Egypt constitute the northern part of the socalled the Arabian Nubian Shield (ANS), which are exposed mainly in the Eastern Desert (ED) and the Sinai Peninsula (Figure 1). The general geological settings of the rock assemblages of the CED were grouped into two major lithotectonic units [8]. The structurally lower one, the "infrastructure," is composed of gneisses and migmatites that crop out in dome structures, such as the Meatiq, Sibai, and Hafafit domes. The overlying unit, the "suprastructure," includes the Neoproterozoic ophiolite complexes and island arc-related metavolcanic and metasedimentary rocks. The suprastructure is also known as the Pan-African Nappe Complex [9]. The juvenile crust in the ED of Egypt is characterized by four main rock units: (i) a gneiss assemblage that comprises the core complexes, (ii) an ophiolite-island arc assemblage, (iii) granitoid intrusions, and (iv) nonmetamorphosed to weakly metamorphosed Dokhan volcanics and Hammamat molasses sediments that

unconformably overlie the suprastructure in places [10]. Most of the rock sequences are generally deformed and metamorphosed due to the Neoproterozoic East African orogeny. Below, the most important geological aspects of the main rock units are

A number of medium- to high-grade core complexes or "gneissic domes" have been described in the ED. These infrastructures consist of upper amphibolite facies gneisses, amphibolites, migmatites as well as granitic gneisses. They exposed in several places in the ED, including the Meatiq, El Shalul, the Migif-Hafafit, and

Eastern Desert of Egypt.

briefly summarized:

3

2.1 Granite gneisses and migmatites

2. Geologic overview of the Eastern Desert of Egypt

#### Figure 1.

(a) Inset geological sketch map of NE Africa showing the Arabian-Nubian Shield, the Saharan Metacraton, and Archaean and Palaeoproterozoic crust that was remobilized during the Neoproterozoic and (b) geological map of the Eastern Desert of Egypt showing study areas [15].

### Geochemistry and Tectonic Setting of Neoproterozoic Rocks from the Arabian-Nubian Shield… DOI: http://dx.doi.org/10.5772/intechopen.82519

The Precambrian basement of the Eastern Desert of Egypt (ED) is a part of the Arabian-Nubian Shield (ANS) and are exposed mainly in the Eastern Desert and Sinai (Figure 1). The Eastern Desert of Egypt comprises variably deformed and metamorphosed volcanic, plutonic, and sedimentary rocks of Precambrian age, unconformably overlain by Cretaceous sediments. The Eastern Desert of Egypt is classified into three domains: north, central, and south [6], all revealing different aspects of the region's protracted and intense Neoproterozoic episode of deformation and igneous activity. The Central Eastern Desert (CED) preserves the oldest (Tonian-Cryogenian) history and also best preserves Ediacaran deformation as well as associated (Hammamat) basins. The Southern Eastern Desert (SED) lacks BIF, Ediacaran sedimentary or volcanic successions such as the Hammamat Group and Dokhan Volcanics, whereas the CED does not [7]. The Northern Eastern Desert (NED) is very different than either the CED or the SED. Dokhan volcanics and Hammamat molasses sediments are of widespread occurrence, whereas ophiolites are absent and gneisses are rare.

The reconstructions of this chapter are based on a compiled data of geochemistry and obtained ages on the rock units constituting the Eastern Desert of Egypt. Geochemical data are based on combination of major elements, trace elements, rare earth element (REE) distributions as well as isotope data. In this contribution, I build on previous geological and geochemical studies on the different rock units forming the ED for many years of research to summarize the most important geochemical characteristics of the different rock units and to provide some important information regarding the geochemical dynamic and evolution of Neoproterozoic crust of the ED. This chapter reviews the scope of current geochemical and isotopic datasets for the ANS, with particular emphasis on the Eastern Desert of Egypt.
