Continental rifting and the implications for plate tectonic reconstructions

Abstract

Previous plate tectonic reconstructions have tried to recreate the pre‐rifting (Pangea) configuration of the continents by matching contours or lineaments that are thought to represent the continental boundaries. Such reconstructions have the inherent assumptions that no extension occurs within the continent during rifting, that the continental boundaries are isochrons, and that the continents rift without distortion. This paper proposes a model for continental breakup with distortion, where ocean basins are formed by propagating rifts. This model challenges the assumptions made by previous reconstructions and presents a new method for representing the prerift geometry of the continents. As rifts propagate through a continent, the region in front of the rift extends by continental faulting and crustal thinning while the region behind the rift expands by seafloor spreading. The propagating rift model implies that large amounts of continental extension (up to 150 km) occur and that the continental boundaries are not isochrons. This extension due to rifting results in ‘apparent’ overlap when the continents are returned to their original configuration. Because of the gradational nature of this extension, the best representation of the pre‐rift configuration is obtained by matching the initial rifting point and having overlap increase in the direction of rift propagation. The overlap is equivalent to the amount of extension that has taken place on both continental edges. Reconstructions based on this model are presented for the Gulf of California, the Gulf of Aden, the Norwegian‐Greenland Sea, and the South Atlantic Ocean. They are able to resolve the discrepancies that occur when rigid plate tectonics are applied. This model has implications that can be used to predict the age and structure of the continental shelves and the location and orientation of the oldest magnetic isochrons.