Arabia-Somalia plate kinematics, evolution of the Aden-OwenCarlsberg triple junction, and opening of the Gulf of Aden

New geophysical data collected at the Aden-Owen-Carlsberg (AOC) triple junction between the Arabia, India, and Somalia plates are combined with all available magnetic data across the Gulf of Aden to determine the detailed Arabia-Somalia plate kinematics over the past 20 Myr. We reconstruct the history of opening of the Gulf of Aden, including the penetration of the Sheba Ridge into the African continent and the evolution of the triple junction since its formation. Magnetic data evidence three stages of ridge propagation from east to west. Seafloor spreading initiated ∼20 Myr ago along a 200 kmlong ridge portion located immediately west of the Owen fracture zone. A second 500 kmlong ridge portion developed westward up to the Alula-Fartak transform fault before Chron 5D (17.5 Ma). Before Chron 5C (16.0 Ma), a third 700 km-long ridge portion was emplaced between the Alula-Fartak transform fault and the western end of the Gulf of Aden (45°E). Between 20 and 16 Ma, the Sheba Ridge propagated over a distance of 1400 km at an extremely fast average rate of 35 cm yr -1. The ridge propagation resulted from the Arabia-Somalia rigid plate rotation about a stationary pole. Since Chron 5C (16.0 Ma), the spreading rate of the Sheba Ridge decreased first rapidly until 10 Ma and then more slowly. The evolution of the AOC triple junction is marked by a change of configuration around 10 Ma, with the formation of a new Arabia-India plate boundary. Part of the Arabian plate was then transferred to the Indian plate. Copyright 2010 by the American Geophysical Union.