India's Mysterious Move toward Eurasia Finally Solved

That's not to say that India is currently on the move, but about 80 million years ago it was, rapidly drifting toward Eurasia for mysterious reasons that are finally known to scientists.

According to new research published in the journal Nature Geoscience, India was likely 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.

More than 140 million years ago, India was part of an immense supercontinent 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 five centimeters per year. That didn't so much startle scientists as when the continent suddenly sped up roughly 80 million years ago, racing north at about 15 centimeters per year. That's about twice as fast as the fastest modern tectonic drift. The continent collided with Eurasia about 50 million years ago, and has remained in that same spot ever since.

For years, scientists have struggled to understand this record-holding episode of continental drift. Some had believed volcanic activity was the culprit, but it turns out dual sinking tectonic plates may have had enough pulling power to double India's drift velocity.

"In earth science, it's hard to be completely sure of anything," Leigh Royden, a professor of geology and geophysics in MIT's Department of Earth, Atmospheric and Planetary Sciences, said in a statement. "But there are so many pieces of evidence that all fit together here that we're pretty convinced."

The team found relics of what may have been two subduction zones by sampling and dating rocks from the Himalayan region, which was created by the collision. Then, using a model for a double subduction system, they concluded that India's drift velocity could have depended on the width of the subducting plates, and the distance between them. If the plates are relatively narrow and far apart, they would likely cause India to drift at a faster rate.

Based on the geologic record, India's migration appears to have started about 120 million years ago, when Gondwana began to break apart.

"When you look at simulations of Gondwana breaking up, the plates kind of start to move, and then India comes slowly off of Antarctica, and suddenly it just zooms across - it's very dramatic," Royden said.

It kept up this rapid pace for about 30 million years before coming to a crashing halt, quite literally.

Based on the dimensions of the recovered plates, the researchers calculated that India would have sped up from 50 to 150 millimeters per year right around 80 million years ago. While previous studies have calculated similar rates for India's drift, this is the first evidence that double subduction acted as the continent's driving force.

"It's a lucky coincidence of events," explained researcher Oliver Jagoutz. "There were a lot of changes going on in that time period, including climate, that may be explained by this phenomenon. So we have a few ideas we want to look at in the future."

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