Morphostructural development of the Eritrean rift flank (southern Red Sea) inferred from apatite fission track analysis

[1] The Red Sea is one of the best exposed young rift basins in the world. Its flanks on both the African and Arabian sides are characterized by basement uplifts parallel to the margins and by active erosion. Through the integration of 37 new apatite fission track (FT) analyses and regional geology, we elucidate the uplift and denudational history of the Eritrean continental margin along the southern Red Sea and, in particular, the development, timing, and past and present morphostructural features of its onshore portion. FT data indicate that at around 20 Ma, the Eritrean margin was affected by a crustal cooling event due to a postrifting accelerated phase of denudation. This cooling has the same age as those already detected on the conjugate Arabian margin (Yemen and Saudi Arabia). FT ages increase from 10-20 to 300-400 Ma with increasing distance and elevation from the coastal areas toward the interior. This trend indicates a diminishing amount of eroded section in the same direction. We use FT and structural data to define the position of the main border fault along the margin where the original scarp was located. We estimate rates of vertical denudation of 190-200 m/Myr at the border fault and of less than or equal to 60-70 m/Myr on the plateau. On the basis of these new data, we argue against an Oligocene tectonic unroofing of the margin through a low-angle detachment assumed by previous authors, but we maintain the essential role of the erosional denudation in the development of present margin morphology.