Definition - What does Nappe mean?
A Nappe is a massive rock with a sheetlike body which is raised above the thrust fault around 2 to 5 kilometers from its initial position. It is found on the overriding plates of the active subduction zones or in the compressional tectonic settings such as the continental collision zones. A Nappe is formed when the mass of one rock is thrust over the mass of another rock mostly on the low angle fault planes. Fensters, imbricate thrust stacks, klippe and recumbent folds could be the resulting structures.
Petropedia explains Nappe
Nappes are usually considered as compressional structures; however, some exceptions can be found along the low angle faults among the gravitational slides. The movement of large masses of the rocks could be influenced by various forces which may act subsequently or together.
They are classified into two types - Basement and cover Nappes.
- Basement Nappes: They generally consist of the crystalline basement rocks which form thick skinned style. They can create their independent super units by reaching a large thickness.
- Cover Nappes: They are the superficial Nappes which are generally composed of sedimentary rocks forming the upper part of the crust that forms the thin skinned style.