- nappe
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/nap/, n.1. Geol. a large mass of rock thrust a considerable distance along a nearly horizontal fault plane or in an overturned anticlinal fold.2. Geom. one of the two equal sections of a cone.
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In geology, a large body or sheet of rock that has been moved by faulting or folding a distance of about 1 mi (1.5 km) or more from its original position.A nappe may be the hanging wall of a low-angle thrust fault (a fracture in the rocks of the Earth's crust caused by contraction), or it may be a large recumbent fold (i.e., an undulation in the stratified rocks that have an essentially horizontal axial plane); both processes position older rocks over younger rocks.* * *
▪ geologyin geology, large body or sheet of rock that has been moved a distance of about 2 km (1.2 miles) or more from its original position by faulting or folding. A nappe may be the hanging wall of a low-angle thrust fault (a fracture in the rocks of the Earth's crust caused by contraction), or it may be a large recumbent fold (i.e., an undulation in the stratified rocks of the Earth's crust having an essentially horizontal axial plane); both processes position older rocks over younger rocks. In places, erosion may cut into the nappe so deeply that a circular or elliptical patch of the younger, underlying rock is exposed and completely surrounded by the older rock; this patch is called a fenster, or window. Fensters generally occur in topographic basins or deep, V-shaped valleys. Elsewhere, an eroded, isolated remnant of the older rock or nappe may be completely surrounded by the younger, underlying rock; this is known as a klippe, or thrust outlier. Mythen Peak in the Alps in a typical example of a klippe.* * *
Universalium. 2010.
