The role of surface processes in basin inversion and breakup unconformity

Luke Mondy , Patrice F Rey, Guillaume Duclaux 

At divergent plate boundaries, extensional tectonics lead to subsidence, continental rifting and the formation of continental margins. Yet, within this extensional context, transient compressional structures (stress inversion) and phases of uplift (depth inversion) are frequently recorded with no corresponding change in plate motion. Changes in gravitational potential energy during the rifting process have been invoked as a possible source of compressional stresses, but their magnitude, timing and relationship with depth inversions remain unclear. Using high-resolution 2D numerical experiments of the full rifting process, we track the dynamic interplay between the far-field tectonic forces, loading and unloading of the surface via surface processes, and gravitational body forces. Our results show that rift basins tend to localize compressive stresses, they record transient phases of compressional stresses up to 30 MPa and experience a profound depth inversion, 2 km in magnitude, when sediment supply ceases, providing a novel explanation for the breakup unconformity, a well-documented phase of regional uplift typically associated to continental breakup.