Décollement

Décollement (/dɛ.kɒll.mɔːn/; from the French décoller, 'to detach from') is a gliding plane between two rock masses, also known as a basal detachment fault. Décollements are a deformational structure, resulting in independent styles of deformation in the rocks above and below the fault. They are associated with both compressional settings (involving folding and overthrusting) and extensional settings.

The term was first used by geologists studying the structure of the Swiss Jura Mountains, coined in 1907 by A. Buxtorf, who released a paper that theorized that the Jura is the frontal part of a décollement at the base of a nappe, rooted in the faraway Swiss Alps.Marcel Alexandre Bertrand published a paper in 1884 that dealt with Alpine nappism. Thin-skinned tectonics was implied in that paper but the actual term was not used until Buxtorf's 1907 publication.

Décollements are caused by surface forces, which 'push' at converging plate boundaries, facilitated by body forces (gravity sliding). Mechanically weak layers in strata allow the development of stepped thrusts (either over- or underthrusts), which originate at subduction zones and emerge deep in the foreland. Rock bodies with differing lithologies have different characteristics of tectonic deformation. They can behave in a brittle manner above the décollement surface, with intense ductile deformation below the décollement surface. Décollement horizons may be at depths as great as 10 km and form due to high compressibility between differing rock bodies or along planes of high pore pressures.

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