The Egyptian Nubian Shield Within the Frame of the Arabian–Nubian Shield

Abstract

Gondwana Supercontinent in eastern and southern Africa formed by collision and amalgamation of two crustal plates, provisionally named East Gondwana and West Gondwana and the Mozambique Ocean intake between 841 and 632 Ma. East Gondwana consists of the Arabian–Nubian Shield (ANS) and the older crystalline basement in Madagascar, India, Antarctica and Australia, while West Gondwana consists of much of Africa and South America. Collision and amalgamation of East and West Gondwana formed the East African Orogeny. The supercontinent of Gondwana ranged from Neoproterozoic (~550 Ma ago) to Carboniferous (~320 Ma ago). Gondwana became the largest continental crust during the Paleozoic Era (~100 million km2). During the Carboniferous, Gondwana amalgamated with Euramerica resulting in the formation of the supercontinent, Pangaea. Three orogeneses were recognized during the 1990s: the East African Orogeny (650–800 Ma), Kuunga Orogeny (including the Malagasy Orogeny in southern Madagascar) (550 Ma)—the collision between East Gondwana and East Africa in two steps—and the Brasiliano Orogeny (660–530 Ma)—the collision between South American and African Cratons. Formation of arcs in the ANS occurred over a ~300-million-year period including supercontinent Rodinia break-up and the assembly of supercontinent Gondwana. The ANS represents one of the best documented examples of Late Proterozoic to Early Paleozoic (950–450 Ma) crustal growth through processes of lateral arc–arc terrane accretion. The tectonic development of the ANS spans three phases spanning over 600 Ma: accumulation of arc terrains inside the Hijaz Magmatic Arc, accompanied by accretion of the Hijaz Magmatic Arc against the Nile Craton and reworking of the accreted arc after accretion. The Egyptian Nubian Shield (ENS) covers ~100,000 km2, crops out along the Red Sea Hills in the Eastern Desert and southern Sinai, as well as limited areas in the south Western Desert (Oweinat area, 2673 ± 21 Ma). The ENE covers the northeastern part of the East African Orogeny and stretches over approximately 800 km parallel with the Red Sea coast between latitudes 22° 00΄ 00˝ and 28° 40΄ 00˝ N. The rocks are covered by Nubia sandstone, Miocene and later sediments in their western and eastern margins. The Eastern Desert of Egypt is divided into three domains, namely, the northern Eastern Desert (NED), central Eastern Desert (CED) and southern Eastern Desert (SED); these domains were developed in different tectonic settings and show a characteristic younging from (SED) to (NED). Geologically, gneisses, migmatites and schists dominate the SED as the oldest units, and are followed by ophiolites, volcanic arc lithologies and granitoid plutons. The amount of ophiolites increases and forms with the arc metavolcanics the main types in the CED. The ophiolites and the metavolcanics are occasionally unconformably and tectonically overlained by Dokhan volcanics and molasse sediments. The older gneisses and migmatites form prominent domal structures (e.g. Meatiq, Sibai, Hafafit, El-Shalul). Syn-tectonic and late tectonic granitoids are also present. The NED is characterized by younger rocks, such as Gattarian granites, Dokhan volcanics and Hammamat molasse sediments, whereas older rock types rarely occur. The bulk of the crust of the SED was created prior to 650 Ma, while the major pulses of the CED occurred in the interval (685–575 Ma). In the NED and Sinai, the crust was principally formed in the period (625–575 Ma).