The mystery of India’s rapid drift
India got a geologic boost that accelerated its drift toward Eurasia 80 million years ago, researchers suggest. The speed of the resulting impact created the Himalayas.
A study in the journal Nature Geoscience on May 4, 2015 by team of MIT geologists offers an explanation for why the continent of India moved so rapidly toward Eurasia 80 million years ago.
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. Then, about 80 million years ago, the continent suddenly sped up, racing north at about 15 centimeters 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 MIT have offered up an answer: 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. 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 relatively narrow and far apart, they would likely cause India to drift at a faster rate.
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 toward Eurasia some 80 million years ago.
Based on the geologic record, India’s migration appears to have started about 120 million years ago, when Gondwana began to break apart. India was sent adrift across what was then the Tethys Ocean — an immense body of water that separated Gondwana from Eurasia. India drifted along at an unremarkable 40 millimeters per year until about 80 million years ago, when it suddenly sped up to 150 millimeters per year. India kept up this velocity for another 30 million years before hitting the brakes — just when the continent collided with Eurasia.
Leigh Royden is a professor of geology and geophysics in MIT’s Department of Earth, Atmospheric and Planetary Sciences. Royden said:
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.
In 2011, scientists believed they had identified the driving force behind India’s fast drift: a plume of magma that welled up from the Earth’s mantle. According to their hypothesis, the plume created a volcanic jet of material underneath India, which the subcontinent could effectively “surf” at high speed.
However, when others modeled this scenario, they found that any volcanic activity would have lasted, at most, for five million years — not nearly enough time to account for India’s 30 million years of high-velocity drift.
Instead, the MIT researchers believe that India’s fast drift may be explained by the subduction of two plates: the tectonic plate carrying India and a second plate in the middle of the Tethys Ocean.
Celal Sengor is a professor of geological engineering at Istanbul Technical University who was not involved in this research. Sengor said:
India was going far too fast after it parted company with Africa-Madagascar and Australia. … Its speed northward, with respect to the rest of Eurasia, was faster than any plate motion we know today, or have inferred in the past across a single plate boundary. This paper not only has changed some of our ideas on the paleotectonics and paleogeography of the neo-Tethys, but has given us a new model about what double subductions can do.
Bottom line: According to a study published May 4, 2015 in the journal Nature Geoscience, India got a geologic boost that accelerated its drift toward Eurasia 80 million years ago.
Source…..www.earthsky.org
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