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Field surveys in the Gulf of Suez-Northern Red Sea area revealed the structural pattern and evolution of this tertiary continental rift and provided constraints on the continental rifting process. The structure has been controlled, at every scale, by four major trends of faults: N0°–20°E, N100°–120°E, N140°E–160°E and N40°–60°E. Observations of sealed faults and folds and superposed structures and the detailed analysis of the fault surfaces are coherent and indicate that as least two different stages of deformation characterize the evolution of the rift. The initiation of the rift (late Oligocene-Aquitanian) corresponds to the creation of large rhomboidal basins, weakly subsident and partly bounded by oblique strike-slip faults. This framework, which resulted from the reactivation of inherited weakness zone in the basement, controlled the subsequent creation of large tilted blocks (upper Aquitanian-lower Burdigalian). These structures were trangressed by the upper Burdigalian deposits. Then the blocks were sliced by a secondary horst and graben pattern, which was progressively sealed by middle Miocene units. Since the upper Miocene, the deformation has been focused along some major faults located in the central part of the rift. The determination of paleostresses from measurements of striae confirms that the initiation of the rift was controlled by a tectonic regime characterized by an horizontal compressive stress parallel to the rift, and its subsequent evolution was controlled by triaxial and radial extensional regimes with horizontal minimum stress (σ3) predominantly trending N70°–80°E. The rifting process was not induced by regional doming but by a new distribution of intraplate stresses at approximately Oligocene-Miocene time (passive rift). Uplift of the rift shoulders began in the upper Burdigalian. Cross sections of the rift emphasize its asymmetry: large basement blocks are tilted toward the edge of the rift where a major, recently active fault and a distinct morphological unit, which we call a “banquette,” are located. Several homogeneous tilt direction provinces can be defined. They are separated by transverse hinge zones that correspond to inherited basement trends. Rifting deformation is expressed in the basement by steep faults arranged in a zig-zag pattern and in Neogene-Quaternary sediments by steep faults and listric faults associated with decollements. Therefore the style of shallow deformation cannot be extrapolated to deeper levels. Structures formed during the beginning of the rift show different charateristics according to their orientation, but their initial shape was generally complicated by later deformation. |
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