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The Red Sea depression has been considered by previous workers to be (1) a graben, with downdropped center block, resulting from compressive forces, or (2) a paar, or depression caused by the moving apart of two crustal blocks, and thus essentially a tensional feature. It is to the second hypothesis that the present writers subscribe. It is suggested that movement took place between four blocks: Block I, northeast Africa west of Suez-Red Sea and north of the Ethiopian rift valley; Block II, the Arabian peninsula; Block III, the Sinai peninsula; and Block IV, the "Horn of Africa" east of the rift valleys. All of the structural features of the region may be related to various movements between these blocks, including the Gulf of Aden, the rift valleys of Ethiopia, the Dead ea depression, and the mountains of the Levant.
During the Mesozoic the most important movements were epeirogenic. Faulting and volcanism occurred in the Jurassic and Cretaceous. By the end of lower Eocene time compressional stresses developed in the northern regions, while there were tensional forces in the south. It was probably then that the Gulf of Suez-Red Sea paar opened and folds appeared in the Levant. At the southern end of the Red Sea there was strong northwest-southeast faulting accompanied by basalt extrusion in the Ethiopian rifts. Folding and faulting in the northern region were accompanied by one or more periods of epeirogenic uplift which caused unconformities at the end of lower Eocene, middle Eocene, and Oligocene time.
Beginning in the lower Miocene, the "Horn of Africa" began to separate from the Arabian peninsula. This separation became complete as the Arabian block moved toward the Tethys geosyncline, and during the Pliocene the Red Sea and Gulf of Aden were joined.
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