Sedimentary
Basement assemblages in Pan-African Collision zones, Eastern Desert, Egypt
Abd ElGhani I. Ragab, Ahmed A.
Dardier1, Hamdy H. Abd ElNaby1 and Adel A. Abd ElWahed1
Dept. Geol., Fac. Sciences, Ain Shams Univ.; 1Nuclear
Material Authority, Cairo, Egypt |
The Pan-African belt of the Eastern Desert of
Egypt is believed by many researchers to have evolved by accretion of island arcs. The
collision zones between island arcs, ex. Gabal Meatiq-Wadi Atalla-Wadi Hammamat area, are
characterized by the occurrence of:
1) Ophiolitic melange belt representing former accretionary wedges,
2) regional migmatitic gneisses representing a former accretionary forearc basin, and
3) conglomerates and lithic arenites representing former foreland molasse-type basins.
Presented here are three new maps and a first documentation of some field observations
about the sedimentary boundaries between these tectono-sedimentary assemblages at Wadi
Atalla (west of the Meatiq gneiss dome), and at the southern part of Abu Swayel gneisses
and the gneisses at Gabal Naag, south Eastern Desert. This is done to give a better
picture of the tectono-sedimentary relationships of collision zones based on actual field
evidences.
The migmatitic gneisses occur over the margin of the ophiolitic melange belts suggesting
angular unconformable deposition of forearc basin sediments over the high-angle subduction
melange accretionary wedges. This occurred at convergent plate margins during the
precollision stage as observed in many modern accretionary complexes. The Wadi Hammamat
foreland molasse-type metasediments, west of the Meatiq gneiss dome, are parallel to the
high-angle ophiolitic melange structural elements facing the foreland east of the Um Had
granites. This suggests accretion in a remnant sea basin as a wedge between the subduction
melange and the underthrust crustal plate margin during the ocean closure stage.
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