Application of Magnetic Susceptibility and Its Anisotropy in Deciphering the Tectonic Evolution of the Pan-African Belt of Egypt

Abstract

The Pan-African belt (PAB) of Egypt outcrops mainly in the Eastern Desert and Southern Sinai. It occupies the northwestern sector of the Arabian-Nubian Shield (ANS) and lies at the northern continuation of the East African Orogen (EAO). The EAO comprises the low-grade greenschist facies lithologies of the ANS to the north and the deeper crustal equivalents of the Mozambique belt (MO) to the south. It is regarded by many workers to form a major suture zone delineating the oblique convergence (transpression) between East and West Gondwanaland. The PAB represents a complete succession of the Neoproterozoic basement encountered elsewhere in the ANS. It is recently interpreted as composed of a series of Neoproterozoic intra-oceanic arcs amalgamated during the climax of the Pan-African Orogeny c. 630 Ma. It consists of four major rock groups: high-grade gneisses and migmatites, arc-type volcanic/volcano–sedimentary sequence and dismembered ophiolites, Hammamat Sediments and Dokhan Volcanics and voluminous granitoids. These rock groups have undergone a prolonged history of deformation involving three ANS-scale deformation events (D1–D3) (Hamimi et al. 2019). The D1 resulted from arc accretion and led to the formation of S-, SE-, SW- and NE-directed thrusts, as well as N-directed escape of the ANS, via N- to NNW-directed thrusts and thrust-propagation folds. The D2 deformation was a post-accretion shortening phase, that produced transpressive structures, including NNW–SSE trending sinistral transcurrent shears (e.g. Nugrus and Atalla Shear Zones), the dextral transcurrent shearing along with NE-directed mega shears (e.g. Idfu-Mersa Alam and Qena Safaga Shear Zones) and the post-accretionary shear zone-related gneiss domes. The D3 deformation was an extensional long-lasting phase associated with the crustal relaxation following the Gondwana assembly. This chapter addresses the application of the anisotropy of magnetic susceptibility (AMS), as an appropriate petrofabric technique, in unravelling and deciphering the tectonic evolution of the PAB. Emphasis will be given to some key areas where such a technique has been used in an adequate manner.