Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

India joined with Asia 10 million years later than previously thought

07.02.2013
New timeline suggests India's size before this collision was much smaller than generally assumed

The peaks of the Himalayas are a modern remnant of massive tectonic forces that fused India with Asia tens of millions of years ago. Previous estimates have suggested this collision occurred about 50 million years ago, as India, moving northward at a rapid pace, crushed up against Eurasia.

The crumple zone between the two plates gave rise to the Himalayas, which today bear geologic traces of both India and Asia. Geologists have sought to characterize the rocks of the Himalayas in order to retrace one of the planet's most dramatic tectonic collisions.

Now researchers at MIT have found that the collision between India and Asia occurred only 40 million years ago — 10 million years later than previously thought. The scientists analyzed the composition of rocks from two regions in the Himalayas, and discovered evidence of two separate collisional events: As India crept steadily northward, it first collided with a string of islands 50 million years ago, before plowing into the Eurasian continental plate 10 million years later.

Oliver Jagoutz, assistant professor of geology in MIT's Department of Earth, Atmospheric and Planetary Sciences, says the results, which will be published in Earth and Planetary Science Letters, change the timeline for a well-known tectonic story.

"India came running full speed at Asia and boom, they collided," says Jagoutz, an author of the paper. "But we actually don't think it was one collision … this changes dramatically the way we think India works."

'How great was Greater India?'

In particular, Jagoutz says, the group's findings may change scientists' ideas about the size of India before it collided with Asia. At the time of collision, part of the ancient Indian plate — known as "Greater India" — slid underneath the Eurasian plate.

What we see of India's surface today is much smaller than it was 50 million years ago. It's not clear how much of India lies beneath Asia, but scientists believe the answer may come partly from knowing how fast the Indian plate migrates, and exactly when the continent collided with Asia.

"The real question is, 'How great was Greater India?'" Jagoutz says. "If you know when India hit, you know the size of Greater India."

By dating the Indian-Eurasian collision to 10 million years later than previous estimates, Jagoutz and his colleagues conclude that Greater India must have been much smaller than scientists have thought.

"India moved more than 10 centimeters a year," Jagoutz says. "Ten million years [later] is 1,000 kilometers less in convergence. That is a real difference."

Leafing through the literature

To pinpoint exactly when the Indian-Eurasian collision occurred, the team first looked to a similar but more recent tectonic example. Over the last 2 million years, the Australian continental plate slowly collided with a string of islands known as the Sunda Arc. Geologists have studied the region as an example of an early-stage continental collision.

Jagoutz and his colleagues reviewed the geologic literature on Oceania's rock composition. In particular, the team looked for telltale isotopes — chemical elements that morph depending on factors like time and tectonic deformation. The researchers identified two main isotopic systems in the region's rocks: one in which the element lutetium decays to hafnium, and another in which samarium decays to neodymium. From their analysis of the literature, the researchers found that rocks high in neodymium and hafnium isotopes likely formed before Australia collided with the islands. Rocks high in neodymium and hafnium probably formed after the collision.

Heading to the Himalayas

Once the team identified the isotopic signatures for collision, it looked for similar signatures in rocks gathered from the Himalayas.

Since 2000, Jagoutz has trekked to the northwest corner of the Himalayas, a region of Pakistan and India called the Kohistan-Ladakh Arc. This block of mountains is thought to have been a string of islands that was sandwiched between the two continents as they collided. Jagoutz traversed the mountainous terrain with pack mules and sledgehammers, carving out rock samples from the region's northern and southern borders. His team has brought back three tons of rocks, which he and his colleagues analyzed for signature isotopes.

The researchers split the rocks, and separated out more than 3,000 zircons — micron-long crystals containing isotopic ratios. Jagoutz and his colleagues first determined the age of each zircon using another isotopic system, in which uranium turns slowly to lead with time. The team then measured the ratios of strontium to neodymium, and lutetium to hafnium, to determine the presence of a collision, keeping track of where each zircon was originally found (along the region's northern or southern border).

The team found a very clear signature: Rocks older than 50 million years contained exactly the same ratio of isotopes in both the northern and southern samples. However, Jagoutz found that rocks younger than 50 million years, along the southern boundary of the Kohistan-Ladakh Arc, suddenly exhibited a range of isotopic ratios, indicating a dramatic tectonic event. Along the arc's northern boundary, the same sudden change in isotopes occurs, but only in rocks younger than 40 million years.

Taken together, the evidence supports a new timeline of collisional events: Fifty million years ago, India collided with a string of islands, pushing the island arc northward. Ten million years later, India collided with the Eurasian plate, sandwiching the string of islands, now known as the Kohistan-Ladakh Arc, between the massive continents.

"If you actually go back in the literature to the 1970s and '80s, people thought this was the right way," Jagoutz says. "Then somehow the literature went in another direction, and people largely forgot this possibility. Now this opens up a lot of new ideas."

This research was supported by a grant from the National Science Foundation.

Written by Jennifer Chu, MIT News Office

Caroline McCall | EurekAlert!
Further information:
http://www.mit.edu

More articles from Earth Sciences:

nachricht Underground fungi detected from space
04.05.2016 | Smithsonian Tropical Research Institute

nachricht How much does groundwater contribute to sea level rise?
03.05.2016 | International Institute for Applied Systems Analysis (IIASA)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Nuclear Pores Captured on Film

Using an ultra fast-scanning atomic force microscope, a team of researchers from the University of Basel has filmed “living” nuclear pore complexes at work for the first time. Nuclear pores are molecular machines that control the traffic entering or exiting the cell nucleus. In their article published in Nature Nanotechnology, the researchers explain how the passage of unwanted molecules is prevented by rapidly moving molecular “tentacles” inside the pore.

Using high-speed AFM, Roderick Lim, Argovia Professor at the Biozentrum and the Swiss Nanoscience Institute of the University of Basel, has not only directly...

Im Focus: 2+1 is Not Always 3 - In the microworld unity is not always strength

If a person pushes a broken-down car alone, there is a certain effect. If another person helps, the result is the sum of their efforts. If two micro-particles are pushing another microparticle, however, the resulting effect may not necessarily be the sum their efforts. A recent study published in Nature Communications, measured this odd effect that scientists call “many body.”

In the microscopic world, where the modern miniaturized machines at the new frontiers of technology operate, as long as we are in the presence of two...

Im Focus: Tiny microbots that can clean up water

Researchers from the Max Planck Institute Stuttgart have developed self-propelled tiny ‘microbots’ that can remove lead or organic pollution from contaminated water.

Working with colleagues in Barcelona and Singapore, Samuel Sánchez’s group used graphene oxide to make their microscale motors, which are able to adsorb lead...

Im Focus: ORNL researchers discover new state of water molecule

Neutron scattering and computational modeling have revealed unique and unexpected behavior of water molecules under extreme confinement that is unmatched by any known gas, liquid or solid states.

In a paper published in Physical Review Letters, researchers at the Department of Energy's Oak Ridge National Laboratory describe a new tunneling state of...

Im Focus: Bionic Lightweight Design researchers of the Alfred Wegener Institute at Hannover Messe 2016

Honeycomb structures as the basic building block for industrial applications presented using holo pyramid

Researchers of the Alfred Wegener Institute (AWI) will introduce their latest developments in the field of bionic lightweight design at Hannover Messe from 25...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

The “AC21 International Forum 2016” is About to Begin

27.04.2016 | Event News

Soft switching combines efficiency and improved electro-magnetic compatibility

15.04.2016 | Event News

Grid-Supportive Buildings Give Boost to Renewable Energy Integration

12.04.2016 | Event News

 
Latest News

New fabrication and thermo-optical tuning of whispering gallery microlasers

04.05.2016 | Physics and Astronomy

Introducing the disposable laser

04.05.2016 | Physics and Astronomy

A new vortex identification method for 3-D complex flow

04.05.2016 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>