Nappe

a large-scale geological structure (tens of kilometres) occurring as a sheet of rock which has been pushed over a fault plane or THRUST at the base. They are formed due to compression, but an alternative mechanism is the sliding due to gravity along a low angle fault, as seen in the Swiss Alps. In many cases, the origin of nappes may be due to a combination of both mechanisms.

Taken from Dictionary of Science

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In geology, a nappe is a large sheetlike body of rock that has been moved more than 2 km (1.2 miles) or 5 km from its original position. Nappes form during continental plate collisions, when folds are sheared so much that they fold back over on themselves and break apart. The resulting structure is a large-scale recumbent fold. The term stems from the French word for tablecloth.

Nappes or nappe belts are a major feature of the European Alps, Carpathians and Balkans. The concept was developed by the French geologists who unraveled the complex tectonic history of the Alps, led by M.A. Bertrand, who identified the feature as nappe de charriage. In Switzerland it was A. Escher von der Linth and M. Lugeon. At the same time, nappe structure was investigated in northwestern Scotland by Ch. Lapworth. The Austroalpine nappes of the eastern Alps consist of a series of three thrust-faulted nappe stacks which overlie the three older Penninic nappes in this very complex system.

Taken from Wikipedia