Evolution of Continental Rift Systems in the Light of Plate Tectonics

Abstract

Rifts occur at all stages of the Wilson Cycle of opening and closing of oceans, but those most likely to be preserved form either at continental breakup or continental collision. All preserved rifts are “failed rifts” because they have not “succeeded” in developing into oceans. Hundreds of ancient rifts ranging up to 2.6 Ga in age have been recognized. Axial mafic dike systems have been located in both ancient and active rifts and activation of the basalt-eclogite transition in these systems may be an effective way of promoting the repeated subsidence that characterizes many rift complexes, such as those of the North Sea. Ancient rifts striking into fold belts are known as aulacogens (after Shatski). Recognition (after Wilson) that many fold belts mark places where oceans have closed has made it possible to interpret numerous aulacogens as rifts formed at continental rupture and to interpret their history in plate-tectonic terms. In many ways the best known of rift systems are those formed at the opening of the Atlantic Ocean because they have been subjected to intense petroleum exploration. Eleven classes of rifts with diverse histories can be distinguished among the rifts presently facing Atlantic-type continental margins and aulacogen histories are even more diverse.