Thrust sheet

In geology, a nappe or thrust sheet is a large sheetlike body of rock that has been moved more than 2 km (1.2 mi) or 5 km (3.1 mi) above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision zones or on the overriding plate in active subduction zones. Nappes form when a mass of rock is forced (or "thrust") over another rock mass, typically on a low angle fault plane. The resulting structure may include large-scale recumbent folds, shearing along the fault plane, imbricate thrust stacks, fensters and klippe.

The term stems from the French word for tablecloth in allusion to a rumpled tablecloth being pushed across a table.

Nappes or nappe belts are a major feature of the European Alps, Carpathians and Balkans. Since the 19th century many geologists have uncovered areas with large-scale overthrusts. Some of these were substantiated with paleontological evidence. The concept was developed by Marcel Alexandre Bertrand, who unraveled the complex tectonic history of the Alps and identified the feature as nappe de charriage. He reinterpreted earlier studies by Arnold Escher von der Linth and Albert Heim in the Glarus Alps. His work in Switzerland influenced Escher and Maurice Lugeon. Several years later, nappe structure was investigated in northwestern Scotland by Charles Lapworth. Lugeon later transferred the ideas of nappes to the Carpathians.

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