Plate Tectonics and the Collision

1. Tectonic Plates:
   • The Earth’s lithosphere is broken into several big and small tectonic plates. The Indian Plate and the Eurasian Plate are among these big plates.
2. Initial Movement:
   • About 100 million years ago during the late Cretaceous period, the Indian Plate started moving northwards away from the ancient supercontinent Gondwana at a rate of about 15-20 cm per year. This movement was driven by the spreading centre at the Indian Ocean’s mid-ocean ridge.
3. Closing of the Tethys Sea:
   • As the Indian Plate moved north, it started closing the Tethys Sea, an ancient ocean that existed between the Indian subcontinent and the Eurasian Plate.
4. Subduction and Continental Collision:
   • The dense oceanic crust of the Indian Plate initially subducted beneath the Eurasian Plate. This subduction led to volcanic activity and the formation of an arc of volcanic islands. But as the continental crust of the Indian Plate approached, it was too buoyant to subduct easily.
   • About 50 million years ago, the Indian continental crust collided with the Eurasian continental crust. This collision slowed down the northward movement of the Indian Plate to about 5 cm per year.

Formation of the Himalayas

1. Crustal Shortening and Thickening:
   • The collision caused immense compressive forces that led to crustal shortening. The crust thickened as one plate was pushed over the other and the Himalayan mountain range was uplifted.
   • The Indian Plate was pushed beneath the Eurasian Plate but since both plates are made of continental crust, they buckled and folded rather than subducting smoothly.
2. Fold and Thrust Belts:
   • The intense pressure and stress caused large scale folding and faulting of the rock layers. This process created a series of parallel mountain ranges and valleys, known as fold and thrust belts.
   • The Main Central Thrust, the Main Boundary Thrust and the Himalayan Frontal Thrust are the major fault lines that play a significant role in the structural formation of the Himalayas.
3. Ongoing Tectonic Activity:
   • The Himalayas are still rising due to the ongoing convergence of the Indian Plate and the Eurasian Plate. This tectonic activity also causes frequent earthquakes in the region.
   • The uplift and erosion are in a dynamic balance, where the mountain range is continuously being built up by tectonic forces and worn down by erosion.

Key Features and Evidence

1. High Peaks:
   • The Himalayas have some of the world’s highest peaks, including Mount Everest and K2, as a result of these geodynamic processes.
2. Marine Fossils:
   • Marine fossils found in high altitude regions of the Himalayas are evidence of the ancient Tethys Sea and the collision. These fossils show that these rocks were once part of the ocean floor before they were uplifted to their current height.
3. Metamorphism:
   • The intense pressure and temperature conditions during the collision led to metamorphism of rocks. High grade metamorphic rocks like schists and gneisses are found extensively in the Himalayan region.

In summary, the Himalayan mountain range was formed by the northward movement and collision of the Indian Plate with the Eurasian Plate, resulting in crustal shortening, thickening, and the uplift of the highest mountain range in the world.