A Recipe for Exotic Continental Fragment Formation: Key Constraints From Numerical Rift Models

Abstract The Wilson Cycle describes the opening and closing of oceans, generating new plate boundaries at continental rifts, and extinguishing ancient plate boundaries with continental collisions (creating a continental suture). However, the general view of the Wilson Cycle does not fully explain more complex tectonic scenarios. For example, rifting can create exotic continental fragments, where a piece of continent becomes displaced from its principal part and stranded on another tectonic plate. Despite the prevalence of stranded fragments in the geological record, their formation processes remain poorly understood. Here, we conducted 2‐D numerical rift models to systematically test the tectonic influence of a variety of inherited geological structures that could be generated from the closing of an old plate boundary. Through automated detection of continental breakup and measurement of continental fragment dimensions, the models show that fragment width is directly controlled by the geometry of the inherited structures, including the dip angle and extent of the old subduction suture, as well as the extent of orogenic deformation. However, the initial geotherm, strain and rheological weaknesses in both the crust and mantle lithosphere, along with the divergence rate, can influence strain localization during rifting. Notably, a very ductile lithosphere leads to prolonged delocalized thinning and wider rifts. Overall, the models produce continental fragments in widths ∼175–350 km, aligning with many geological examples. Moreover, our work provides key physical constraints that can be applied in future regional applications and highlights the role of different forms of structural inheritance during rifting and continental fragment formation.