Self-consistent rolling-hinge model for the evolution of large-offset low-angle normal faults

The nature of the physical processes responsible for the formation of conti nental and oceanic metamorphic core complexes is widely debated. The contro versy focuses primarily on whether the low-angle normal faults observed in these environments formed and slipped at low angles or were rotated from an original high-angle orientation after large offsets. We describe a self-co nsistent numerical model for the extension of a brittle layer that can spon taneously produce normal-fault structures. In our formulation, a fault or f aults form because strength is locally reduced with increasing strain. If t he reduction in fault strength is <similar to 10% of the total strength of the layer, then faults lock after an offset smaller than the layer thicknes s and new faults form. Larger strength reduction leads to single faults tha t continue to slip no matter how large the fault offset. If the strength re duction occurs by the loss of cohesion, then we see the unlimited offset fa ults for layers <11-22 km thick for reasonable values of cohesion. The key result of this study is that structures very similar to those observed in b oth oceanic and continental core complexes are produced by rotation of the inactive part of the model fault after very large offset.