Geological Divisions of Himalayas
From a geological point of view, Himalayas can be divided into four zones. These zones are identified on the basis of age and composition of the rocks.
This region lies north of the Greater Himalayas. Rocks in this region date back from the Palaeozoic Era to Pleistocene Epoch.
Central or Himalayan Zone
This zone has Isoclinal folds and it includes the Greater Himalayas and some parts of Lesser Himalayas. The Isoclinal folds are essentially parallel to each other and thus approximately parallel to the axial plane. This region has abundant rocks such as granite as well as metamorphic rocks like schists and gneiss. This region also has sedimentary rocks.
Himalayan Nappe Zone
A nappe (literally means tablecloth) is a large sheetlike body of rock that has been moved some kilometers away from its original position. Nappes form during continental plate collisions, when folds are sheared so much that they fold back over on themselves and break apart. The resulting structure is a large-scale recumbent fold. The nappes are most common in Kashmir and Kumaun Himalayas.
Outer or Sub-Himalayan Zone
This zone includes the Siwalik range which is mainly composed of sedimentary deposits of upper tertiary period. This implies that the Shivalik hills are mainly derived from the eroded material of the main Himalayan ranges.