PROTEROZOIC TO EARLY PALEOZOIC TECTONIC EVOLUTION OF THE CENTRAL EASTERN DESERT OF EGYPT: STRUCTURAL, PETROLOGICAL, AND GEOCHRONOLOGICAL CONSTRAINTS
We conclude that Wadi El Dabbah represents remnants of an island arc formed on top of a south dipping subduction zone. Oceanic crust in its fore- and back- arc basins formed 850–700 Ma, contemporaneously with arc activity. Three pulses of arc eruptions delivered volcaniclastic debris to these basins, imposing anoxic conditions that led to increased Fe2+ in seawater. During periods of arc quiescence, Fe2+ was oxidized and precipitated as BIF precursor minerals. During the Pan-African orogeny, back arc basin lithosphere and overlying BIFs and volcaniclastics were emplaced northward onto the arc. Stacking of thrust sheets tapering to the north caused regional metamorphism with highest grades in the southern CED. Transpression along the northeastern margin of the arc closed the fore-arc basin, emplacing ophiolites north of Wadi El Dabbah with SW verging folds. Subduction polarity reversal led to intrusion of syntectonic granitoids into the ophiolitic sequence, and eruption of Dokhan volcanics in NED. Ages of c. 680 Ma on syntectonic granitic intrusions suggest that the collisional stage of the Pan-African Orogeny began c.10–40 Ma earlier than previously thought.