Relationships between transform directions and alkaline igneous rock lineaments in Africa and South America

Alkaline igneous complexes form distinct lineaments in Angola, South West Africa, Brazil, and Uruguay. Each of these lineaments lie along small circles centered on the Cretaceous and present poles of rotation for the South Atlantic and can be correlated with a unique fracture zone/transform fault that offsets the Mid-Atlantic ridge. It is suggested that the lineaments are continental expressions of these fracture zones. Isotopic age determinations from complexes in the lineaments lie in the range 120–135 my and 50–80 my and are consistent with the current model for the evolution of the South Atlantic and the origin of the lineaments as suggested here.