Segmentation of the Northern Red Sea: Evidence From Ocean Deeps

The Red Sea (RS) represents a young oceanic rift that resembles the evolutionary stages from continental rifting to seafloor spreading. From 24°N-29°N, the northern RS is thought to be in the stage of continental rifting. South of 24°N there is a transition area with isolated spots of seafloor spreading that migrates into a well established Mid Ocean Ridge. However, a detailed scheme of the transition from rifting to drifting is not available, because massive evaporite layers (up to 7 km thick) mask the basement and prevent seismic observations of the basement in most areas of the RS. Thus, near surface structures and potential field data are the only sources of information to establish a model for the evolutionary history of the RS. The conspicuous RS deeps that are commonly distributed along the Axial Depression and Axial Trough are often interpreted as incipient seafloor spreading centers. Three northern RS deeps were investigated during the R/V Meteor cruises M44/3 and M52/3. A combined analysis of new seismic and hydroacoustic data with magnetic data led to the assumption that the Northern RS (24°N-29°N) can be subdivided into two segments that show distinct evolutionary stages. At 25.5°N, the Axial Depression changes its trend: NW-SE north of 25.5°N and N-S (more diffuse) south of this spot. In the NW-SE segment the Conrad-, Shaban- and an unnamed deep are accompanied by strong magnetic anomalies, indicating magmatic activity. Normal faults bound the steep escarpment-like slopes. The shape, internal structure and orientation of the fault system point to the tectonic development of these deeps. The N-S segment exhibits deeps (Kebrit-, Vema-Deeps) that do not show magnetic anomalies. Fault system and shape (Kebrit Deep) indicate a development as collapse structure, caused by dissolution and subrosion of the evaporites. The NW-SE segment is more developed, because it is orientated normal to the RS extension. The stretched continental crust is affected by magmatic intrusions whose near surface impacts are the steep-sloped ocean deeps. We characterize this segment as 'volcanic type'. The N-S segment is less developed and because of the lack of magmatic evidences it is termed 'non-volcanic type'.