At http://phys.org/print321252239.html … an international team of geoscientists have published a paper in Nature Communications (May, 2015) which they hope will revolve one of the problems inherent to Plate Tectonics. When South America split apart from Africa between 150 and 120 million years ago, bringing the South Atlantic into existence, the continental margins formed – but they are surprisingly different. You don't get the impression there is much wrong with Plate Tectonics when you read your average text book. These kind of problems are not for public consumption. Along off shore Angola there are 200km wide continental leftovers – left behind by the rifting. In Brazil the margin is an abrupt transition between continental crust and oceanic crust.
We are told geoscientists have struggled to understand why both sides are not symmetric. It seems that an explanation has now been found – or purports to address the problem. Rifts are capable of being moved horizontally – moving sideways over 100s of km. During rift movement the crust on one side is weakened by hot upwelling material from the Mantle whereas on the other side of the rift it is cooler and becomes inactive very quickly. The sideways rift is what is left behind along the coast of Angola – and presumably in other locations too (though these are not mentioned in the abstract).