The Himalayan and the Alpine mountain building process is now better explained with the help of the Theory of Plate Tectonics. This theory has replaced the former geosynclinals theory of mountain building. The entire crust of the earth has been divided into six plates viz; the Pacific Plate, the Eurasian Plate, the American Plate, the Indian Plate, the African Plate and the Antarctic Plate.
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The collision of the plates leads to the building of stresses within the plates and the continental rocks above, resulting in folding, faulting and igneous activity. According to the Plate Tectonic Theory, “The Himalayan ranges were formed when the Indian Plate was driven northwards and pushed beneath the Eurasian Plate.
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With the advance of the Indian Plate towards the north, the Tethys started contracting about 65-70 million years ago. About 30-60 million years ago, the two plates came closer and the Tethys Sea crust began to fracture into thrust edges. About 20-30 million years ago, the Himalayan range started emerging.”
The Geological study of the Himalayas indicates that the entire mountain-building process occurred in three main phases:
(i) First Phase or Karakoram Phase is indicated by the uplift of the Central Himalayan axis in Oligocene Age. This is largely composed of old crystalline and sedimentary rocks.
(ii) Second Phase or Sirmurian Phase took place during the Miocene Age. This phase is marked by washing up of the sediments of the basin which occupied Potwar region of Pakistan.
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(iii) Third Phase or Shivalikian Phase is represented by the folding of the Shivaliks. This happened in the Post-Piliocene time. It is believed that this phase of uplift is still continuing.
Prior to the above-mentioned three stages, the Karakoram and the other associated mountain ranges were uplifted. This uplift was completed in the Cretaceous period.
Findings of geologists and archaeologists provide numerous evidences to prove that the Himalayas are very young and the mountain-building process is still continuing. Following are some of the outstanding evidences:
(i) Karewas:
These are tilted beds of the lake deposits of Kashmir at altitudes of 1500 to 1850 metres on the flanks of Pir Panjal range. The presence of these Karewas strongly suggests that the process of Himalayan uplift continued as late as Pliocene and Pleistocene Age.
(ii) Fossils:
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The post-Tertiary fossils of some mammals found in the sub-Himalayan foothills suggests the continuing uplifting process in the Pleistocene Age.
(iii) River Terraces:
Archaeologists have found curious stone tools in many of the river terraces of Himalayas, especially the Solan and in the Shivalik deposits near Chandigarh. These are typical examples of human artefacts of Palaeolithic times. This indicates that the last phase of Himalayan uplift took place after the appearance of early man in this area.
It is interesting to note that the present characteristics of the Himalayan features are the result of various agents of weathering and denudation, especially the glaciers and running water. These agents have been active ever since these mountains emerged out of the sea.