![]() ![]() "Dextral transpression in Late Cretaceous continental collision, Sanandaj–Sirjan Zone, western Iran". ^ Mohajjel, Mohammad Fergusson, Christopher L ()."Erosional control on the structural evolution of a transpressional thrust complex on the Alpine fault, New Zealand". "State of stress near the San Andreas fault: Implications for wrench tectonics". "Late Cenozoic transpression in southwestern Mongolia and the Gobi Altai-Tien Shan connection". "The evolution of forearc structures along an oblique convergent margin, central Aleutian Arc". "A structural transect across the Mongolian Western Altai: Active transpressional mountain building in central Asia". Geological Society, London, Special Publications. "Tectonics of strike-slip restraining and releasing bends". Structural Geology - Cambridge Books Online - Cambridge University Press. Galeh–Doz pluton (Sanandaj–Sirjan Zone, Iran)."Big Bend" of the San Andreas Fault Zone, (California, USA).Altai Mountains (Western Mongolia and Southern Siberia, Russia).They have been theorized to occur on extraterrestrial bodies, like Jupiter's icy moon Europa and on Venus. Restraining bends are widespread on the Earth's surface, from sub-outcrop-scale examples to large scale mountain ranges. In plan view we see them form contractional strike-slip duplexes, subparallel reverse or oblique-slip contractional faults that are bounded by two strike-slip segments. As seen in deeply eroded outcrop exposures or from subsurface geophysical surveys, restraining bends commonly define positive flower structures. These are areas of positive relief (topographic uplift), crustal shortening, and exhumation of crystalline basement. Geologists may also refer to a restraining bend as a left bend. When a sinistral fault steps to the right or a dextral fault steps to the left, a restraining bend is formed. The type of structures which form along the strike-slip fault depend on the sense of slip relative to the sense of stepping. 5830 m high Altun Shan mountains formed at a restraining bend on the sinistral Altyn Tagh faultĪ fault bend, or fault stepover, forms when individual segments of the fault overlap and link together. Restraining bend A contractional duplex that has developed at the bend/stepover along a strike-slip fault. The complete geometry presented by all structural elements in the zone is used to constrain the actual boundary displacements. In these zones, the lineations are between horizontal and vertical. It is also common for non-vertical transpressional zones to have a significant component of shearing parallel to the dipline of the zone boundary. Pure shear-dominated transpression usually gives steep lineations, while simple shear-dominated transpression favors horizontal lineations. Commonly developed features include transposition foliations, lineations, stylolites, folds, and reverse faults. Transpressional shear zones are characterized by an association of structures that suggest zone-normal shortening and zone-parallel shearing. More locally, transpression occurs within restraining bends in strike-slip fault zones. ![]() Transpression that occurs on a regional scale along plate boundaries is characterized by oblique convergence. During shortening, unless material is lost, transpression produces vertical thickening in the crust. The relative amounts of shortening and strike-slip can be expressed in the convergence angle alpha which ranges from zero (ideal strike-slip) to 90 degrees (ideal convergence). It is generally very unlikely that a deforming body will experience "pure" shortening or "pure" strike-slip. This movement ends up resulting in oblique shear. In geology, transpression is a type of strike-slip deformation that deviates from simple shear because of a simultaneous component of shortening perpendicular to the fault plane. Type of strike-slip deformation Simple model for transpression: strike-slip zone with an additional and simultaneous shortening across the zone. ![]()
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