Kinematics of the Sinai triple junction and a two-phase model of Arabia-Africa rifting

Summary The breakup of Arabia from Africa started at 40–50 Ma in the East African Rift system and concentrated from about 20 Ma around the Red Sea. Presently, the most active system centres along the Gulf of Aden, Red Sea and Dead Sea shear. Two less active features, the Gulf of Suez and East African Rift meet the main boundary at what have often been considered to be active triple junctions (the southern tip of Sinai and Afar). This paper focuses on the continental Sinai triple junction near 27°30′N. Almost no reliable kinematic data can be found in the Red Sea. Only total motion based on a fit of coastlines is available. Yet, the mechanical basis for this is now known to be wrong. We propose a mechanical interpretation that retains the same pole of ARA-NUB motion, with a reduced amount of total opening. The best data come from the Dead Sea shear: 100 km of left-lateral displacement occurred over the last 20, or more likely 15 Ma (subsidence event in the Gulf of Suez). The pull-apart basins in the Gulf of Elat provide the best constraints on the azimuth of SIN-ARA motion. Four models of SIN-ARA-NUB kinematics are proposed depending on whether the Gulf of Suez is; (i) now extinct, (ii) still opening in the original direction, (iii) in a state of left-lateral shear, (iv) in a state of right-lateral shear. Total SIN-NUB motion is unlikely to exceed 1–2 mm yr−1. We propose a two-phase history of break-up, first along the East African Rift/Red Sea/Gulf of Suez, superseded at ∼ 15 Ma by the present Gulf of Aden/Red Sea/Dead Sea shear. Distributed extension now occurs in the Afar and northern Red Sea deforming zones towards which three localized rifts propagate. The Sinai and Afar ‘triple junctions’ are actually kinks where plate boundaries that were not active at the same time are superimposed.