What is Nappes ?

Nappes (ग्रीवाखंड / क्षेप संवलन):

In structural geology and geomorphology, a Nappe (ग्रीवाखंड) is a large sheet or body of rock that has been transported a substantial distance (often tens of kilometers) over underlying rock strata along a nearly horizontal thrust fault plane:

• 1. Mechanism of Formation (Compressional Folding):
  • Intense, continuous lateral tectonic compression forces a symmetrical fold to develop into an Overturned Fold and subsequently into a Recumbent Fold (where the axial plane becomes almost horizontal).
  • When compressive stress exceeds rock elasticity, the lower limb breaks along a low-angle Thrust Fault, sliding the upper rock mass far over the native younger strata (Allod/Allochthonous sheet).
• 2. Geological Examples:
  • Widespread throughout the young fold mountains of the Himalayas (e.g., Krol Nappe, Garhwal Nappe, Kashmir Nappe) and the Alps of Europe (Helvetic and Penninic Nappes).
• 3. Associated Erosional Landforms: Klippe (isolated outlier of nappe) and Fenster / Tectonic Window.