The Northern Red Sea in Transition from Rifting to Drifting-Lessons Learned from Ocean Deeps

Abstract

The transition from continental rifting to seafloor spreading can be observed along the 2,000 km length of the Red Sea Rift system. Whereas the southern Red Sea shows seafloor spreading since 5 Ma and the central part gives evidence of a transitional stage, the northern Red Sea is thought to represent the latest stage of continental rifting. Ocean deeps along the rift axis are considered to be first seafloor spreading cells that will accrete sometime in the future to a continuous spreading axis. The northern Red Sea deeps are isolated structures often associated with single volcanic edifices in comparison with the further developed larger central Red Sea deeps where small spreading ridges are active. Our analysis of the northern Red Sea deeps showed that not all deeps can be related to initial seafloor spreading cells. Two types of ocean deeps were identified: (a) volcanic and tectonically impacted deeps that opened by a lateral tear of the Miocene evaporites (salt) and Plio-Quaternary overburden; (b) non-volcanic deeps built by subsidence of Plio-Quaternary sediments due to evaporite subrosion processes. These deeps develop as collapse structures. The volcanic deeps can be correlated with their positions in NW--SE-oriented segments of the Red Sea which are consequently termed volcanic segments. The N--S segment, linking the volcanically active NW--SE segments, is termed as ``non-volcanic segment'' as no volcanic activity is known, in agreement with the magnetic data that show no major anomalies. Accordingly, the deep that was analyzed in this segment is interpreted as a collapse-related structure. However, collapse-type ocean deeps are not limited to the non-volcanic segments as subrosion processes due to hydrothermal circulation are possible at any part of the axial depression. The combined interpretation of bathymetry and seismic reflection profiles gives further insight into lateral salt gliding. Salt rises are present where the salt flows above basement faults. The internal reflection characteristic of the salt changes laterally from reflection-free to stratified, which suggests significant salt deformation during the salt deposition. Acoustically transparent halite accumulated locally and evolving rim synclines were filled by stratified evaporite facies.