Geodetic Constraints on the Geodynamic Evolution of the Red Sea

Abstract

We use geodetic, plate tectonic, and geologic observations to quantitatively reconstruct the geologic evolution of the Red Sea and Gulf of Aden since separation of Arabia from Africa in the Late Oligocene. Rifting initiated at 22 ± 3 Ma roughly simultaneously along the full strike of the proto-Red Sea and Gulf of Aden. Rifting began along pre-existing zones of weakness associated with a Pan-African Precambrian collisional suture shortly after the Afro-Arabia Plate was weakened by impingement of the African hot spot (*30 Ma). The initial phase of continental rifting followed a roughly linear trend from the Gulf of Suez in the north, to the Bab-al-Mandab in the south where the Afar Triple Junction (junction of Red Sea, Gulf of Aden, and East African rifts) was located at that time. The initial rate of extension across the rift was roughly half the present-day rate. At 11 ± 2 Ma, the rate of rifting doubled to the present-day rate (24 ± 1 mm/year in the south [*12°N] and 7 ± 1 mm/year in the north [*27°N]) and the configuration of rifting changed in both the northern and southern Red Sea. This time corresponds to the initiation of ocean spreading (i.e., complete severing of the continental lithosphere and intrusion of rift basalts) along the full extent of the Gulf of Aden. The changes in the S Red Sea involved the propagation of the Afar Triple Junction westward to its present location (*11.5°N, 42°E), the transfer of rifting from the S Red Sea (Bab-al- Mandab) to the more N–S-oriented Danakil Depression, and accompanying CCW rotation of the Danakil Block with respect to Africa. In the northern Red Sea, rifting transferred from the Gulf of Suez to the more N–S-oriented Gulf of Aqaba/Dead Sea fault system. The rate of rifting has not changed significantly since that time (i.e., 11 ± 2 Ma). The initiation of rifting at 22 ± 3 Ma corresponds temporally with slowing of Africa–Eurasia convergence by a factor of *2 and the changes at 11 ± 2 Ma with a second phase of slowing of Africa–Eurasia convergence, while Arabia–Eurasia convergence has remained roughly unchanged since >30 Ma. These observations are consistent with simple models where changes in Africa– Arabia–Eurasia relative plate motions are the fundamental cause of post-Oligocene Middle East and Mediterranean tectonics. Based on the simultaneity between full ocean spreading along the Gulf of Aden and a doubling of the extension rate across the Red Sea, and the change to more N–S-oriented rifting in both the northern and southern Red Sea, we hypothesize that slowing of Africa–Eurasia convergence resulted from a decrease in slab pull on the African Plate across the evolving AR-AF plate boundary.