Polyphase Folding in Nugrus-Sikeit Area South Eastern Desert, Egypt

Abstract

lithological constitution of Nugrus-Sikeit area comprises a sequence of dismembered ophiolites, tectonic melange association and arc assemblage. These older rocks are intensively deformed and intruded by intracratonic association, which within the mapped area, is represented by gabbros and the associated hornblendite together with younger granites. Planar and linear mesoscopic structures exhibited by the rocks of Nugrus-Sikeit area indicate that these rocks are involved in superimposed folding events and at least three fold generations (F1, F2 & F3) can be recognized. The F1 folds resulted in isoclined folding of S0, and other primary structures around WNW-ESE axes. This phase represents the main folding that affected the area. Besides establishing the WNW-ESE pattern of rock units, it was also responsible for the transposition of S0 into penetrative surfaces S1 accompanying low to medium grade regional metamorphism. The F2 folds refolded the F1 folds into upright to overturned and even recumbent folds about NW-SE axes together with the crenulation of S1 surfaces producing crenulation cleavage S2? The F3 folds are of mild intensity compared to the F1 and F2 generations. It neither appeared to disturb the orientation of the earlier structures nor accompanied by strong transposition foliation. Associated folds are of the mesodimension and maintain a fairly constant NNE-SSW trend.