How India slammed into Eurasia at record speed

Geologists at Massachusetts Institute of Technology have found India was pulled northward by the combination of two subduction zones, regions in the Earth’s mantle where the edge of one tectonic plate sinks under another plate

Washington: India set a continental speed record as it crashed into Eurasia 80 million years ago due to a double subduction, a new MIT study has found. In the history of continental drift, India has been a mysterious recordholder, researchers said.

More than 140 million years ago, India was part of an immense super- continent called Gondwana, which covered much of the Southern Hemisphere. Around 120 million years ago, what is now India broke off and started slowly migrating north, at about 5 centimetres per year. Then, about 80 million years ago, the continent suddenly sped up, racing north at about 15 centimetres per year, about twice as fast as the fastest modern tectonic drift. The continent collided with Eurasia about 50 million years ago, giving rise to the Himalayas. For years, scientists have struggled to explain how India could have drifted northward so quickly. Now geologists at Massachusetts Institute of Technology ( MIT) have found India was pulled northward by the combination of two subduction zones, regions in the Earth’s mantle where the edge of one tectonic plate sinks under another plate. As one plate sinks, it pulls along any connected landmasses, according to the study published just days after a devastating 7.9 magnitude earth- quake hit Nepal. The geologists reasoned that two such sinking plates would provide twice the pulling power, doubling India’s drift velocity.

The team found relics of what may have been two subduction zones by sampling and dating rocks from the Himalayan region.

They then developed a model for a double subduction system, and determined that India’s ancient drift velocity could have depended on two factors within the system: the width of the subducting plates, and the distance between them. If the plates are rel- atively narrow and far apart, they would likely cause India to drift at a faster rate, researchers said. The group incorporated the measurements they obtained from the Himalayas into their new model, and found that a double subduction system may indeed have driven India to drift at high speed towards Eurasia some 80 million years ago.

“In Earth science, it’s hard to be completely sure of anything,” said Leigh Royden, a professor of geology and geophysics in MIT’s department of earth, atmospheric and planetary sciences.