Rise of Himalaya (phases)

The rise of Himalaya has been related with the northward drift of the Indian Plate and it’s consequent collision with the Eurasian Plate. Paleomagnetic data from the floor of the India ocean suggests that the northward drift of the India Plate was most rapid during the Paleocene Epoch. This was also the time of the extensive volcanism over the major part of the Indian Peninsula that is now represented by the Deccan Traps. The Indian Plate began it’s rotational movement giving rise to the formation of the syntaxial bend at the north-western extremity of the Himalayan mountains.

The Paleocene sea that formed a part of the continuous sea connecting the Arabian sea and the Bay of Bengal across the north part of the have receded towards the west and east during the Early Eocene.

This marine transgression continued till emergence of Himalaya towards the end of tertiary period. Eocene is also marked by the transgression. After the brief period of marine regression during the Oligocene epoch, the western and eastern parts of the peninsula were once again inundated by shallow sea that marked the commencement of the Neogene Period. During the Pliocene the sea started withdrawing from the India subcontinent.

Phase -1

The first movement took place during the Late Cretaceous-Early Eocene time. It was accompanied by the emplacement of the Dras volcanics (Indus Ophiolites) along the northern borders of the mountains. The volcanic phase was associated with the development of paleo-island arc system that was formed at the commencement of the Himalayan Orogeny. This phase is also marked by intense deformation, regional metamorphism and emplacement of the granitic gneisses in the deeper parts of the orogen.

The Tethys Sea that ordered the Indian landmass on the northern side was the site of the deposition of thick sequences are now exposed both along the northern (Ladakh) and southern (Lesser Himalaya) parts of the Himalayan ranges.

Phase – 2

The second major upheaval took place during the Late Eocene time when the region comprising the Tethyan Himalaya was uplifted to form a landmass attached with the Indian landmass. This tectonic phase was also accompanied by the emplacement to tourmaline granites along the core of the High Himalayan ranges. The higher Himalaya also rose above the sea water to comprise a land mass that underwent erosion.

The eroded sediments from rising mountains in the north were laid in narrow basins along the southern parts of the Lesser Himalaya.

The basin that had a shallow marine condition during the Paleocene-Early Eocene time gradually paved way t brackish water and fresh water conditions during the deposition of the Middle Eocene – Miocene sequences.

Phase -3

The third upheaval that took place during Middle Miocene was most pronounced of all the phases of the Himalayan Orogeny. Lesser Himalayan rocks were deformed into broad folds trending parallel to the Himalayan of mountains. Thrusts sheets of crystalline rocks that originated from the southern parts of the Higher were piled one over the other over the mildly deformed Lesser Himalayan sequences.

The Middle Miocene upheaval of the Himalaya resulted in the formation of foredeep basins between the rising Himalaya and the northern edge of the Indian Peninsula. These basins were filled with fluviatile and lacustrine sediments derived from the freshly exposed Himalayan rocks.

The molassic succession of the foredeep basins are made up of coarsening upward sequences. The coarser sediments of the upper parts of the sequences also contain and increasing proportion of clasts that were derived from freshly exposed crystalline rocks of the Higher Himalaya.

Phase -4

The fourth phase of the uplift of the Himalaya took place during the Pliocene – Pleistocene Epochs that lead to the rise of the Shivalik hills comprising the sub-Himalaya or Outer Himalaya. Rise of the Sub-Himalaya also coincided with the onset of the Pleistocene glacial events that brought about a major change in the evolution of the mammalian fauna.

The series of the thrust faults that marked the boundary of the Lesser Himalaya and foredeep basins remained active. In the view of their boundary nature, these faults are referred to as Main Boundary Faults or Thrusts.

Phase -5

The fifth and final phase of the Himalayan upheaval took place after the Pleistocene glaciers had receded into the Higher Himalayan region. This upheaval my be attributed to the isostatic adjustment after the removal of the ice sheet. The movement have not yet completely died down as evidenced by slight adjustments being observed in different parts of the Himalaya.