The crustal evolution of the Arabo-Nubian Massif with special reference to the Sinai Peninsula

Abstract

Abstract The Arabo-Nubian Massif extends over most of NE Africa and Arabia, an area of ∼ 3 × 10 6 km 2 . Studies of the last 20 y have revealed similar evolutionary trends in Saudi Arabia, the Eastern Desert of Egypt, the Sinai Peninsula, and the southern Negev. Until almost the very end of the Precambrian, the area of the present massif was not part of the African craton; its history, starting only ∼ 1000 Ma ago, can be divided into four phases which can be recognized in most, if not all, parts of the Arabo-Nubian Shield. Phase I is characterized by the emplacement of oceanic tholeiites, mainly pillow basalts, and their plutonic equivalents. These rocks overlie ophiolite sequences which are tectonically transported and often strongly disrupted. Phase II (∼ 950–650 Ma ago) is dominated by andesitic volcanism and (quartz-)dioritic intrusions with an island are chemistry. The widely held interpretation of colliding intra-oceanic plates is difficult to reconcile with the non-linear arrangement of the magmatics, the predominance of low facies (greenschist), and the absence of high-pressure (blueschist) metamorphism. During the batholithic Phase III (∼ 640–590 Ma ago), the massif is cratonized. Magmatism is at its maximum, magmas are calc-alkaline and silica-rich, the initial 87 Sr/ 86 Sr ratio, which during the earlier phases did not exceed 0.7030, increases up to 0.7090; the young sialic crust starts participating in magma generation. Granitic plutons are not arranged in belts, but are spread haphazardly over the entire massif. The phase ends with a strong uplift; Arabo-Nubia joins the African craton. The alkaline Phase IV (∼ 590–550 Ma ago) produces (per-)alkaline high-level granites and rhyolites (Katharina Province); it affects the entire Arabo-Nubian Shield, but also all of North and Saharan Africa. Spread out over an area of more than 15 × 10 6 km 2 , it is possibly the largest igneous province known.