Jurassic sea-floor spreading in the eastern Equatorial Atlantic

Abstract

THE history of seafloor spreading in the Equatorial Atlantic is poorly known, having been largely inferred from the configuration of fracture zones and the geometry of magnetic lineations in other parts of the Atlantic (Fig. 1). Uncertainties in determining crustal ages at these low latitudes arise partly because of the small amplitudes of the magnetic anomalies and partly because of structural complexities, the separation of South America and Africa involving movements along closely spaced, east–west fracture zones1–3. In this report we describe a series of magnetic anomalies in the eastern Equatorial Atlantic which can be dated using the Vine–Matthews hypothesis4 and the time scale of geomagnetic reversals derived by Larson and Hilde5. The age of the anomalies provides an important constraint on the timing of the early rifting phase of the Atlantic off Guinea, Sierra Leone and Liberia.