PALEOMAGNETISM OF SOUTH AMERICAN AND AFRICAN ROCKS AND THE AGE OF THE SOUTH ATLANTIC

Abstract

The late Palaeozoic polar path, common to the South American-African block, defines a continuous shift of about 60° from the Late Carboniferous to the Middle Permian. During this episode that block moved away from the South pole. In either-early Middle or late Early Permian time, such movement stopped and a quasi-static period started for the South American-African block which lasted up to the Jurassic. A new and reversible polar shift (about 35°) relative to the South American African block started in either late Jurassic or early Early Cretaceous time; previous palaeomagnetic studies did not recognize this Early Cretaceous polar shift common to the South American-African blook. In late Early Cretaceous time such movement stopped for South American and a quasi-static period started for this continent, which lasted up to the late Late Cretaceous. Palaeomagnetic data for Africa suggest that the Cretaceous polar shift was still Present for this continent in Late Cretaceoui time. This suggests that: i) South America and Africa were joined by their Atlantic margins up to the Early Cretaceous; and ii) the separation of these continenrs and the origin of the South Atlantic took place in late Early Cretaceous time (after the Serra Geral and Kaoko basaltic magmatism). However, the palaeomagnetic data do not rule out the possibility that the initial rifting in the South American- African block has occurred in Early Cretaceous time.