Question

Nappe occurs in which type of fault?
a. Fan fold
b. Recumbent fold
c. Symmetrical fold
d. Overthrust fold

Answer 1

Hint:
 Nappes also goes by the name of thrust sheets and forms the upper region of the crust.
 Nappe, also known as thrust sheet, is a large sheet body of rock that has been moved more than 2 or 5km from its original position above the thrust fault.

Complete solution:
Formation of nappe takes place when a mass of rock is overlapped with another rock mass on a low angle fault plane. It looks like a recumbent folds, shearing along fault lines. They form a compressional tectonic setting overriding plate in subduction zones. Front part of the nappe called the leading edge of nappe is the direction of the movement; secondary thrusts and numerous folds are dew common features called Digitations. When compressed and reduced, it results in a structure which is called Suture. Oftenly there are two types of geological features :

- Klippe or nappe outlier. It’s a small region from the main body that lies on an autochthonous base.
- Window or fault inlier is an area of autochthonous basement uncovered by erosion.

There are two types of nappes -
- Cover Nappes or superficial nappes, composed of sedimentary rocks forming the upper part of the crust.
- Basement Nappes are composed of crystalline rocks. They form independent super units such as Penninic nappes.

Hence, the correct answer is option D.

Note:
They are majorly found in European Alps, Dinarides, Balkans and Carpathians. Marcel Alexandre Bertrand discovered it and named it as nappe de charriage. Then next it was investigated in the northwest part of Scotland by Charles Lapworth.