P. Mann, 2007. "Global catalogue, classification and tectonic origins of restraining- and releasing bends on active and ancient strike-slip fault systems", Tectonics of Strike-Slip Restraining and Releasing Bends, W. D. Cunningham, P. Mann
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Restraining- and releasing bends with similar morphology and structure have been described by many previous studies of strike-slip faults in a variety of active and ancient tectonic settings. Despite the documentation of at least 49 restraining and 144 releasing bends along active and ancient strike-slip faults in the continents and oceans, there is no consensus on how these structural features are named and classified, or how their wide range of structures and morphologies are controlled by the distinctive strike-slip tectonic settings in which they form. In this overview, I have compiled published information on the strike-slip tectonic setting, size, basin and bend type, age, and models for active and ancient releasing and restraining bends. Examples of bends on strike-slip faults are compiled and illustrated from five distinctive active strike-slip settings:
oceanic transforms separating oceanic crust and offsetting mid-oceanic spreading ridges;
long and linear plate-boundary strike-slip fault systems separating two continental plates whose plate-boundary kinematics can be quantified for long distances along strike by a single pole of rotation (e.g. the San Andreas fault system of western North America);
relatively shorter, more arcuate indent-linked strike-slip fault systems bounding escaping continental fragments in zones of continent–continent or arc–continent collision (e.g. the Anatolian plate);
straight to arcuate trench-linked strike-slip fault systems bounding elongate fore-arc slivers generated in active and ancient fore-arc settings by oblique subduction (e.g. Sumatra); and
cratonic strike-slip fault systems removed from active plate boundaries, formed on older crustal faults, but acting as ‘concentrators’ of intraplate stresses.
progressive linkage of en échelon shears within a young evolving shear zone; this model is not applicable to older strike-slip fault traces that have accumulated significant, lateral fault offsets;
formation of lenticular ‘sidewall ripout’ structures at scales ranging from outcrop to regional; ripouts are thought to form as a response to adherence or sticking along an adjacent and relatively straight strike-slip fault zone; this structural concept may help to explain the large number of paired bends embedded within strike-slip systems, sinusoidal curvature along the traces of many strike-slip faults, and the episodic nature of lateral shifts in the main strike-slip fault zone;
interaction of propagating strike-slip faults with pre-existing crustal structures such as ancient rift basins. Propagation of new strike-slip faults and interaction with older structures may occur on plate boundary, indent-linked, and trench-linked strike-slip faults; and
concentration of regional maximum compressive stress on pre-existing, basement fault trends in stable cratonic areas can produce active restraining-bend structures; periodic release of these bend-related stress concentrations is one of the leading causes of intraplate earthquakes within otherwise stable cratons.
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Tectonics of Strike-Slip Restraining and Releasing Bends
Restraining and releasing bends are common, but enigmatic features of strike-slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation. Regional-scale restraining bends are sites of mountain building, transpressional deformation and basement exhumation, whereas releasing bends are sites of topographic subsidence, transtensional deformation, basin sedimentation and possible volcanism and economic mineralization. Because restraining and releasing bends often occur as singular self-contained domains of complex deformation, they are appealing natural laboratories for Earth scientists to study fault processes, earthquake seismology, active faulting and sedimentation, fault and fluid-flow relationships, links between tectonics and topography, tectonic and erosional controls on exhumation, and tectonic geomorphology.
This volume addresses the tectonic complexity and diversity of strike-slip restraining and releasing bends with 18 contributions divided into four thematic sections: (1) a topical review of fault bends and their global distribution; (2) bends, sedimentary basins and earthquake hazards; (3) restraining bends, transpressional deformation and basement controls on development; (4) releasing bends, transtensional deformation and fluid flow.