This week a new theory has been proposed on how India and Asia collided, geographically speaking, in the ‘Cenozoic’ era. It suggests that the collision happened in two stages — one about 50 million years ago and the other about 25-20 million years ago to give a final shape to the present day continent.
Earlier research has estimated the time of this collision and shown that the convergence between Indian and Asian plates produced the ‘archetypical continental collision zone’ comprising the Himalaya mountain belt and the Tibetan Plateau. But how and where was the India–Asia convergence got accommodated after the collision remains a long-standing controversy. The two plates have converged up to around 3,600 km, yet the shortening of the upper crusts of Asia and Himalaya as documented in geological records shows this to be approximately 2,350-km less.
Fresh evidence has now emerged to suggest that that this discrepancy can be explained by ‘subduction of highly extended continental and oceanic Indian lithosphere’ within the Himalaya around that time — 50 and 25 million years ago.
Using paleomagnetic data, researchers have shown that this continental and oceanic “Greater India” resulted from around 2,675 km of North–South extension, accommodated between the Tibetan Himalaya and cratonic India. This happened between 120 and 70 million years ago.
The researchers suggest that approximately 50 million years ago the India–Asia collision was actually a collision of the Tibetan-Himalayan microcontinent with Asia, followed by subduction of the largely oceanic Greater India Basin. According to them, the “hard” India–Asia collision occurred around 25–20 million years ago. This happened alongside deformation in central Asia and rapid exhumation of Greater Himalaya crystalline rocks. All this could have a link with intensification of the Asian monsoon system, the researchers say.
Seismic tomography also reflects this two-stage collision between India and Asia.
Here’s adding a fresh angle to the ever-evolving theory of the India-Asia collision!