Is the African Plate Stationary?

The Walvis Ridge is the trail of a hot spot marking the relative motion of the African plate over the mantle since the opening of the South Atlantic, and the termination of the ridge at Tristan and Gough records the cessation of this relative motion.

Abstract

THE islands of St Helena, Tristan da Cunha and Gough lie respectively 500 km, 450 km and 450 km east of the crest of the Mid-Atlantic Ridge1 (Fig. 1). We believe that they overlie hot spots or convective plumes in the mantle and that the Walvis Ridge is the trail of a hot spot marking the relative motion of the African plate over the mantle since the opening of the South Atlantic2,3. We suggest that the termination of the ridge at Tristan and Gough records the cessation of this relative motion. That this occurred about 25 m.y. ago is indicated by a spreading rate of 1.7 cm/yr/side and because the two islands lie just east of magnetic anomaly six4. Spreading of the sea floor continued and has moved the crest west from the hot spots. The Discovery and Meteor seamount chains are concentric with the Walvis Ridge; they too terminate some distance east of the crest of the Mid-Atlantic Ridge and may also be hot spot trails terminating on the same isochron. The position of Bouvet Island is harder to interpret because of its location at the western end of the Atlantic-Indian Ridge.