décollement

thumb|Fig. 1 Imbricate fan in a thrust system with a basal décollement. The section below the décollement is undeformed basement rock. Above the décollement, deformation has occurred due to compression. A series of branching faults terminating at depth.

Décollement () 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.