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Abstract
At the southwestern part of Sinai peninsula, well exposed highly faulted pre and synrift blocks provide an excellent opportunity to study the tectonic evolution and the paleostress history along the eastern side of the Gulf of Suez. The geomorphological features in the area indicate two main geomorphological types (morphotectonic high land and depressions). The morphometric analyses of Wadi Sidri, Feiran and Araba indicate that these basins have complex geomorphologic history, most probably due to tectonic effects Analysis of the drainage lineation in this area indicates that drainage patterns are mostly structurally controlled. The sedimentary basins study and their relation to the structural evolution in southwestern Sinai area indicate that the area is affected by eight major tectonic events The structural contour maps for the subsurface part and cross-sections for the surface part indicate that the major rifting phase occurred mainly in the Middle Rudeis Formation as a Mid-Clysmic event. Normal and listric faults which are restricted to the rift phase are dominant. These faults exhibit syn-fault sedimentation, which indicates that both of these faults are rejuvenated after the deposition of Lower Miocene sediments. It is concluded from the structural interpretation of the aerial photographs, a TM landsat image, and some field measurements that the macro and minor faults, lineations, and joint planes are mainly trending NW-SE as well as NE-SW. Left-lateral strike-slip faults have a NNE direction. Detailed field measurements of the fault planes and their slickensides made a reconstruction of the stress pattern and tectonic evolution of this area possible. The main faults in this area are normal, listric, and left-lateral strike-slip. In order to collect fault slip data about 137 fault planes and slickensides on them were measured in the field. The data represent nearly a homogeneous mixture of primarily dip motions but some data also show strike-slip motion. The resulting pattern of stress shows that the main extension regime in the area has N 50° - 60° E. This direction is mostly concerted with the extension regime in the Gulf of Suez. About 1100 data of joint planes were measured in the field. Most of these joints are tension joints but there is also a small number of shear ones. The stereographic projection of the poles of these joints shows concentration in the NE and SW directions. This also indicates that the extension direction was NE-SW. The tectonic evolution shows that the tilt of blocks in this area was controlled by normal, listric, and some sinistral strike-slip faults. Estimation of the shape factor in Wadi EI Mokattab, and Wadi Araba indicates that the shape factor (R) is ranging from 00 to 0.1. This value indicates that (J” 1 > (J” 2 = (J” 3. Asymmetric boudins are observed in the Durba-Ekma shear zone. These boudins are formed in limestone layers enclosed by calcareous mudstones. They are found to be contemporaneously formed with the development of the shear zone.
These shear zones were established in Late Burdigalian to Late Miocene during large an extensive extension movement (Mid-Clysmic event) in the Gulf of Suez. The petrographic studies of the dyke systems which intruded in the basement rocks (G. Durba, and G. Arab a) and in pre-rift rocks (G. Qabeliat) have mostly similar mineralogical assemblages. On the basis of major, trace, and rare earth elements analyses and discrimination diagrams, it is found that most of the dykes are alkali and within plate basalts. This points out that these dykes were intruded in an extension regime Therefore, the dyke systems are believed to be coeval with the opening stages of the Gulf of Suez.