Sea-Floor Spreading and Structural Evolution of Southern Red Sea

Abstract

The Red Sea has entered the early stages of continental dispersal, and its structural evolution fundamentally has been the rifting and breaching of continental lithosphere by normal faulting attendant on the process of sea-floor spreading. In Oligocene time, the continental lithosphere of the Red Sea area was bowed into a large regional arch with normal faults across the crest. Subsequently, rifting by normal faults that propagated upward through the brittle part of the lithosphere caused strong subsidence on horst and graben and tilted blocks; this rifting led to an extensive marine incursion, and a thick evaporite sequence was deposited in the restricted, hot, arid, low-latitude setting of the Miocene Red Sea trough. A second rift west of the earlier central or axial Mi cene rift originated in the southern Red Sea area in Pliocene time, and the two features now are evolving concurrently over a distance of at least 400 km. An evaporite section of very shallow marine origin accumulated in the western rift during the Quaternary; it constitutes a modern example of salt accumulating in a narrow, restricted, rifted trough which is forming as a consequence of continental breakup. Although considerable separation has occurred in the Red Sea, the present opposing coastlines were never in contact, because the fragmentation of continental lithosphere was very largely attained by normal faulting. Only if a vertical fault cuts the entire thickness of lithosphere could points on opposite coastlines ever have been contiguous.