DEFORMATION OF THE AFRICAN PLATE AS A CONSEQUENCE OF MEMBRANE STRESS DOMAINS GENERATED BY POST-JURASSIC DRIFT

As plates move across the surface of the earth they change their curvature in response to the changing curvature of the earth and as a consequence membrane stresses are generated. At any particular point within a plate the stress generated will be proportional to the change in radius of curvature at that point. The rate of change of curvature of the geoid is latitude dependent, consequently the calculation of latitude-generated stress (σγ) is relatively straightforward. For a point moving from an initial latitude of γ0 to a latitude of γ: σλ∝ (sin2λ0-sin2λ). By determining the stress generated at a sequence of points within a plate during set time intervals, membrane stress domains can be defined and used to predict the way in which a plate would deform. In West Africa two phases of compression (Coniacian-Santonian and Palaeocene-Eocene) have been observed within the Lower Benue Rift, followed by a phase of extension (starting about 25 m.y. ago and continuing to the present day) across the Cameroun Volcanic Line. Membrane stress domain theory offers an explanation not only for the timing of all three phases of deformation but is also closely in agreement with the best available information for the extent of deformation. The Red Sea Rift and the rift between Madagascar and the rest of the African continent were both initiated in domains of very high membrane stress generation. © 1979.