Formation and evolution of the Himalaya

The Himalaya is a young fold mountain belt formed by the collision of the Indian plate with the Eurasian (Tibetan) plate.

Stages of formation

1. Gondwana stage (about 200 Ma): India was part of the southern supercontinent Gondwanaland. It separated, and the Indian plate began to move northwards at a few cm per year.
2. Tethys Sea: Between India and Eurasia lay the Tethys Ocean. Thick marine sediments collected on its floor and margins.
3. Subduction (about 100-65 Ma): Oceanic crust of Tethys was subducted beneath Eurasia, causing volcanism and uplift on the Tibetan side.
4. Collision (about 50-55 Ma): The Indian continental crust met Eurasia. Being light (buoyant), it could not be subducted, so the sediments were squeezed, folded, thrust and uplifted.
5. Main thrusting and uplift: Large thrust faults formed in sequence towards the south: the Main Central Thrust (MCT), Main Boundary Thrust (MBT) and Main Frontal Thrust (MFT).
6. Continuing movement: India still moves north at about 4-5 cm per year; the Himalaya rises about 5 mm per year, and the continuing convergence causes earthquakes.

 Before:   INDIA  ~~Tethys~~  EURASIA
            ->      sea         
 After:     Himalaya  |  Tibet
            /\/\/\ folds, thrusts

Result

• The Himalaya is divided into the Siwalik (south), Lesser Himalaya, Higher (Greater) Himalaya and Tethys Himalaya (north), separated by thrusts.
• Marine fossils on Everest show the rocks were once sea floor.