STRUCTURAL CHARACTERISTICS OF THE SUEZ RIFT MARGINS

Field study of the Hadahid Block (the eastern margin of the central ha lf-graben of the Suez rift) indicates two listric normal faults at its eastern and western boundaries, the rift-bounding fault and the Hadah id Fault, respectively. These faults were affected by two episodes of movement. The earlier movement (at the initial, Neogene rift opening) led to equal displacements on the two faults whereas the later movemen t (at the mid-Clysmic event, 17 Ma ago) caused the Hadahid Fault to bo und the deep part of the central half-graben. A similar conclusion is also reached for the western margin of the southern half-graben of the rift (Esh El Mellaha and Zeit Blocks). The two listric faults boundin g the margin blocks in these two oppositely tilted half-grabens (Hadah id and Esh El Mellaha Blocks) join at depth into a ramp-flat detachmen t. This geometry of the rift-bounding faults represents an intermediat e stage in the evolution of rift basins. It is preceded by the early r ifting stage where extension is less and oppositely tilted half-graben s are formed (e.g. the ancestral Red Sea - Gulf of Suez rift). Increas ed extension at later stages leads to the prevailance of one system of detachment instead of oppositely dipping detachments of adjacent half -grabens. The central and southern Red Sea have perhaps had this geome try before the onset of seafloor spreading.