The recognition of reactivation during continental deformation

Reactivation involves the accommodation of geologically separable displacement events (intervals >1 Ma) along pre-existing structures. The definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings. In neotectonic environments, reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime. This mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors. Four sets of criteria may be used to recognize reactivation in the geological record: stratigraphic, structural, geochronological and neotectonic. Some structural criteria may not be reliable if used in isolation to identify reactivated structures. Much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend, dip or three-dimensional shape of structures. Numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long-term and may be invoked to explain reactivation. The collage of fault-bounded blocks forming most continents therefore carries a long-term architecture of inheritance which can explain much of the observed complexity of continental deformation zones.