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The Eastern Desert of Egypt contains an exposure of approximately 80,000 km2 (30,000 mi2) of late Precambrian basement between the River Nile and the Red Sea. The dominant lithologic units of the basement are low-grade basaltic and andesitic meta-volcanics and immature metasediments. These are associated with serpentinite-gabbro units, which have been interpreted as fragments of obducted ophiolites, and large syntectonic diorite-tonalite-granodiorite intrusions. A regional unconformity separates the above units from a sequence of molasse-type sediments which are intruded by post-tectonic Pan-African (~ 580 m.y.) granites.
Geographic patterns of age, lithology, petrochemistry, and structure have been interpreted in terms of multistage development and accretion of intra-oceanic island arcs and intervening basins. The age of intrusions, and the depth of crustal exposure, generally increases toward the south. No evidence has yet been reported for ages greater than ~ 1,200 m.y., or unequivocally continental lithologies, among the older units.
Structural analysis suggests that the region was affected by at least two distinct compressional events. The first event involved compression along a northwest-southeast axis, and may be related to an episode of northwest-vergent folding and thrusting, with concomitant magmatic activity. The second event involved compression along a WSW-ENE axis which initiated uplift, molasse-type sedimentation, large-scale open folding along NNW-SSE axes, and WSW-directed thrusting or gravity sliding. The emplacement of the Pan-African granites and rhyolites apparently occurred upon relaxation of the second compressional event, signifying the maturation of the crust of the Eastern Desert of Egypt.
The dominant trends (NNW-SSE and WSW-ENE) of high-angle faults and fractures were well established by the end of the Precambrian. These seem to have controlled the positions of various Phanerozoic features, such as alkaline complexes, local sedimentary basins, and the Red Sea.
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