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The crystalline basement of NE Africa and Arabia has all the geophysical and geological characteristics of continental crust. But, field and petrographic evidence indicate an intraoceanic island arc environment for the mainly volcanoclastic sediments and geochemical data suggest that magmatic products were generated at or above easterly inclined Benioff zones. Some of the mafic-ultramafic masses that lie in NE zones across the region have been identified as ophiolites and the zones are thought to mark the approximate margin of individual arc systems; four or five arc systems are identified. The episodic evolution of these Proterozoic island arcs took c. 600 Ma (1100–500 Ma) before the continental character of the area was attained. As calc-alkaline igneous rocks and intervening ophiolite bodies occur elsewhere in northern Africa, the Pan African island arc model may have wider application.

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