Crustal-Scale Fault Interaction at Rifted Margins and the Formation of Domain-Bounding Breakaway Complexes: Insights From Offshore Norway

The large-magnitude faults that control crustal thinning and excision at rifted margins combine into laterally persistent structural boundaries that separate margin domains of contrasting morphology and structure. We term them breakaway complexes. At the Mid-Norwegian margin, we identify five principal breakaway complexes that separate the proximal, necking, distal, and outer margin domains. Downdip and lateral interactions between the faults that constitute breakaway complexes became fundamental to the evolution of the 3-D margin architecture. Different types of fault interaction are observed along and between these faults, but simple models for fault growth will not fully describe their evolution. These structures operate on the crustal scale, cut large thicknesses of heterogeneously layered lithosphere, and facilitate fundamental margin processes such as deformation coupling and exhumation. Variations in large-magnitude fault geometry, erosional footwall incision, and subsequent differential subsidence along the main breakaway complexes likely record the variable efficiency of these processes. Plain Language Summary Faults that cut large parts of or the entire crust behave differently than the ones that only affect the brittle upper crust. Also, they are much more fundamental in the process of thinning continental crust, which eventually leads to the separation of continents. We now have access to seismic reflection data that are much better than before. Thus, for some margins we are now able to map the lateral extent and evolution of the very large, fundamental structures responsible for margin formation. We have mapped such structures offshore Norway and propose a mapping approach and a new classification of the structures that form rifted margins. Furthermore, the lateral and downdip behavior of these very large structures offers enticing insights into the processes that accompany faulting at this enormous scale. We propose that faults that do the same fundamental job on the margin link up in margin-wide complexes that eventually separate domains of differing internal structure and morphology. Our approach aims to link margin deformation at different scales and will thus be useful for workers in academics and industry.