Preface

Geochemistry has always been a multidisciplinary scientific field, characterized by bringing together and synthesizing knowledge and tools from numerous related subjects. It is also a dynamic field of knowledge which, from its formal origins in the 19th century to the present day, has encountered and confronted new challenges. Without abandoning research in mature fields, such as mineral exploration or the geochemical characterization of tectonic processes, the interest of geochemistry has been directed, in recent decades, to some of the most imminent challenges for our society, such as the effects and possible mitigation of climate change or the impact of our society's habits on the health of people and ecosystems. As has happened since the beginning of this scientific discipline, the development of these new fields of geochemistry is linked to advances in the available instrumental techniques for an increasingly precise characterization of the distribution of elements, substances, mineral species, and isotopes in the different geological and environmental matrices. All the aspects mentioned above about geochemistry are reflected in this book, in which researchers from five continents make use of advanced analytical techniques (i.e. Mössbauer spectroscopy, Itrax X-Ray Fluorescence core scanning), and tools and concepts of nearby or auxiliary disciplines (geophysics, remote sensing, biology) to advance the knowledge of complex geochemical problems.

We would like to thank all contributors greatly for their collaboration and effort in producing this book.

> **Luis Felipe Mazadiego, Eduardo De Miguel Garcia, Miguel Izquierdo-Díaz and Fernando Barrio-Parra** Universidad Politécnica de Madrid, Escuela Técnica Superior de Ingenieros de Minas y Energía, Madrid, Spain

Chapter 1

Egypt

Abstract

Gaafar A. El Bahariya

Egypt, age dating, crustal evolution

1. Introduction

1

Geochemistry and Tectonic

Setting of Neoproterozoic Rocks

from the Arabian-Nubian Shield:

Emphasis on the Eastern Desert of

The Neoproterozoic rocks of the Eastern Desert (ED) of Egypt represent the northwestern part of the Arabian-Nubian Shield (ANS), which was formed during the Pan-African orogenic cycle (950–450). Geochemistry of the different rock units has clarified their compositional variations, tectonic settings, and origins. The ages of these rock units were reported to predict the crustal evolution of the ANS. Island arc volcanic rocks and ophiolitic sequences formed between 700 and 800 Ma, and then, they were obducted in the earlier stage of the Pan-African orogeny. The post-collision stage was characterized by the emplacement of large masses of Dokhan volcanics (610–560 Ma) and shallow level A-type granites (610–550 Ma). Neoproterozoic ophiolites fall geochemically and tectonically into two separate groups: MORB-like ophiolites and SSZ ophiolites of fore-arc tectonic setting. Intra-oceanic island arcs and related inter-arc volcaniclastic sediments are followed by the incorporations of ophiolite fragments into the volcaniclastic matrix to form "ophiolitic mélange" through tectonic and/or concurrent sedimentary and tectonic processes. The "gneissic domes" that are metamorphic core complexes were

previously interpreted to represent a pre-Neoproterozoic. However, recent age data

Keywords: geochemistry, Neoproterozoic, Arabian-Nubian Shield, Eastern Desert,

The Arabian-Nubian Shield (ANS) forms one of the largest exposures of juvenile

continental crust (1000–525 Ma) on Earth [1]. It consists of mainly juvenile

argued that the ED gneissic rocks are juvenile in origin and Neoproterozoic. Granitoid rocks in the ED include older and younger types. Most of the older granitoids are of I-type character, displaying metaluminous, calcalkaline geochemical characteristics plot in the area of volcanic arc granites (VAG), whereas most of the younger granitoids are mainly alkaline of A-type granites and of within-plate tectonic setting (WPG). Nonmetamorphosed Dokhan volcanics and Hammamat molasse sediments formed during the final post-collisional phases.
