Himalayas on the move

The Indian plate is heavy and steadily sinking under Eurasia  

By Tiasa Adhya
Published: Monday 15 February 2010

imageMoving  at a speed of a little above 18 cm per year the Indian continental plate rammed into the Eurasian trench 50 million years ago. The Himalaya erupted under the impact. But that is not where the story ended. The Himalayan tectonic plate is moving towards Central Asia at a speed of 2cm/year—the reason for repeated earthquakes. The lithosphere of the Earth is broken into tectonic plates or slabs underlying each continent. When tectonic plates collide, further movement is impeded. Since the plates are supposedly lighter than the Earth’s mantle, it is unlikely for one to get drawn beneath the other (subduction). Therefore, tectonic plates remain latched onto each other at the surface,” said Chris Houser, assistant geography professor at the Texas University in usa.

But this is where the India-Eurasia collision stops making sense. Geologists have put in 150 years of research into this but are yet to understand it.

Geoscientist Fabio Capitanio from the Monash University in Australia and colleagues from Switzerland and Italy explored the balance of forces between plates during collision. They created a numerical model that focused on the density of the plates rather than the velocities at which they move. Using the model they recreated the Earth at the time the Himalaya was formed.

They found that a part of the Indian plate, comprising the crust and mantle, folded to form the Himalaya upon hitting the Eurasian plate. This made the remaining portion of the Indian slab denser than the underlying mantle and allowed it to slip under the Eurasian plate. Such a continental slab, when subducted, would have only decelerated the motion of the Indian plate but not stalled it, explained the study published in Nature Geoscience on January 10.

“Our approach shows the Himalayan plate is moving the result of which is the upward lift of the Tibetan plateau. Such deformation manifests in earthquakes,” said Capitanio. “The study provides a fresh perspective on the puzzle over events before and after the India-Eurasia collision,” commented Robert Dietmar Muller, professor at the School of Geosciences from the University of Sydney, in the journal.

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