Editing Thrust fault (section)

===Thrust duplex===
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Duplexes occur where two decollement levels are close to each other within a sedimentary sequence, such as the top and base of a relatively strong [[sandstone]] layer bounded by two relatively weak mudstone layers. When a thrust that has propagated along the lower detachment, known as the ''floor thrust'', cuts up to the upper detachment, known as the ''roof thrust'', it forms a ramp within the stronger layer. With continued displacement on the thrust, higher stresses are developed in the footwall of the ramp due to the bend on the fault. This may cause renewed propagation along the floor thrust until it again cuts up to join the roof thrust. Further displacement then takes place via the newly created ramp. This process may repeat many times, forming a series of fault-bounded thrust slices known as ''imbricates'' or [[Horse (geology)|horses]], each with the geometry of a fault-bend fold of small displacement. The final result is typically a lozenge-shaped duplex.

Most duplexes have only small displacements on the bounding faults between the horses, which dip away from the foreland. Occasionally, the displacement on the individual horses is more significant, such that each horse lies more or less vertically above the other; this is known as an ''antiformal stack'' or '''imbricate stack'''. If the individual displacements are still greater, the horses have a foreland dip.

Duplexing is a very efficient mechanism of accommodating the shortening of the crust by thickening the section rather than by folding and deformation.<ref>{{cite journal|last1=Moore|first1=Thomas E.|last2=Potter|first2=Christopher J.|title=Structural Plays in Ellesmerian Sequence and Correlative Strata of the National Petroleum Reserve, Alaska|journal=U.S. Geological Survey Open File Report|series=Open-File Report |volume=03-253|year=2003|doi=10.3133/ofr03253 |url=https://pubs.usgs.gov/of/2003/0253/pdf/of03-253.pdf|access-date=5 July 2022}}</ref>