Continental drift is something that doesn't happen overnight, but in geologic terms India has speedily outrun every other landmass on Earth on its collision course with Eurasia, researchers say.
After breaking off of the Gondwana supercontinent in the Southern Hemisphere about 120 million years ago, India began sliding northward at about 2 inches a year, a pretty average speed for continental drift.
Suddenly, around 80 million years ago, India put the pedal to the metal and started moving at almost half a foot a year, around twice as fast as any continent or tectonic plate is moving today, researchers at the Massachusetts Institute of Technology say.
The result was a impact with Eurasia around 50 million years ago, a cataclysmic impact that created the Himalayas, the tallest mountains on Earth.
That acceleration has always puzzled scientists, but researchers at MIT have suggested an answer; India got some help from two separate subduction zones helping to pull it along.
Subduction zones are regions in the Earth's mantle where the forward edge of one tectonic plate is driven under another plate, with the sinking plate pulling along any landmasses connected to it.
Two sinking plates, one in front of the other, would provide double the "pull," they suggest, which could have doubled the speed of India's northward journey.
"The collision scenario between India and Eurasia is more complex and protracted than most people think," says MIT geologist Oliver Jagoutz, one of the authors of a study appearing in Nature Geoscience.
The researchers say an examination and dating of rocks in the Himalayan region suggests the existence of such a double subduction system, which they modeled based on their findings.
One of the plates was carrying India, they suggest, adjacent to a second plate in the middle of the Tethys Ocean, an ancient and immense body of water separating Gondwana from Eurasia.
Two factors could have affected India's drift velocity, they say: the width of the two subduction plates, and the space separating them.
If the plates were narrow and somewhat far apart, their model showed, they could have accelerated India's drift rate.
"In earth science, it's hard to be completely sure of anything," says geophysics and geology Professor Leigh Royden. "But there are so many pieces of evidence that all fit together here that we're pretty convinced."
"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," she says.
Gondwana is what paleogeographers call the more southerly of two supercontinents that were part of the Pangaea supercontinent that existed from about 510 to 180 million years ago. It included most of today's Southern Hemisphere, including Antarctica, South America, Africa, Madagascar, and the Australian continent. It also included the Arabian Peninsula and the Indian subcontinent, but plate movement now has placed them entirely into the Northern Hemisphere.
