How
India drifted towards Eurasia 80 million years ago
Washington, May 5 For years, scientists have struggled to explain
how India could have drifted northward so quickly. Now, geologists at the Massachusetts
Institute of Technology (MIT) have unearthed India's rapid move toward Eurasia
80 million years ago that later gave rise to the Himalayas.
According to them, 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.
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.
"In the Earth science, it is hard to be completely sure of anything. But
there are so many pieces of evidence that all fit together here that we are
pretty convinced," said Leigh Royden, professor of geology and geophysics
in MIT's department of earth, atmospheric and planetary sciences.
In the history of continental drift, India has been a mysterious record-holder.
More than 140 million years ago, India was part of an immense supercontinent
called Gondwana, which covered much of the southern Hemisphere.
"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 is very dramatic," Royden explained.
Around 120 million years ago, what is now India broke off and started slowly
migrating north at about five 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.
After collecting samples from the Himalayas, the team developed a model of
double subduction involving a northern and a southern plate.
