February 6, 2013
Collision Between India and Asia Occurred 10 Million Years Later Than Previously Thought
Lee Rannals for redOrbit.com — Your Universe Online
MIT researchers found that the collision between India and Asia occurred 40 million years ago, rather than the previous belief of 50 million years ago.
“India came running full speed at Asia and boom, they collided,” Oliver Jagoutz, an author of the paper, said in a statement. “But we actually don´t think it was one collision “¦ this changes dramatically the way we think the India/Asia collision works.”
He said the group's findings may change scientists' ideas about the size of India before it collided with Asia, because if you know when India hit, then you know the size of Greater India.
They concluded that if Greater India took 10 million more years to catch up to Asia, then it must have been smaller than predicted.
“India moved more than [4 inches] a year,” Jagoutz says. “Ten million years [later] is [600 miles] in convergence. That is a real difference,” he noted.
Jagoutz and colleagues first looked to the Australian continental plate, as it collided with a string of islands known as the Sundra Arc over the last 2 million years. This helped to pinpoint exactly when the Indian-Eurasian collision occurred.
They studied the geologic literature on Oceania's rock compassion, looking for isotopes, which are chemical elements that morph depending on factors like time and tectonic deformation. The team identified two main isotopic systems in the region's rock, one of which the element lutetium decays to hafnium, and the other in which strontium decays to neodymium.
The researchers found that rocks high in neodymium and hafnium isotopes likely formed before Australia collided with the islands.
Once they were able to identify the isotopic signatures for collision, they began to look for similar signatures in rocks gathered from the Himalayas.
Since 2000, Jagoutz has been trekking to the northwest corner of the Himalayas, which features a group of mountains thought to have been a string of islands that was sandwiched between the two continents as they collided. He traversed the mountains with pack mules and sledgehammers, collecting rock samples from the region's northern and southern borders.
So far, he and his team have brought back three tons of rock samples, which they used to analyze for the signature isotopes.
They split the rocks, and separated out more than 3,000 zircons, determining the age of each one using another isotopic system. After this, they measured the ratios of strontium to neodymium, and lutetium to hafnium.
The researchers found that rocks older than 50 million years old contained exactly the same ratio of isotopes in both the northern and southern samples. However, rocks younger than 50 million years exhibited a range of isotopic ratios, which indicates a dramatic tectonic event.
The latest evidence also explains a new timeline of collisional events, where 50 million years ago India collided with a string of islands, and 10 million years after that it collided with the Eurasia plate.
“This paper does a great deal to stir up the debate on the topic of the timing of collision,” said Peter Clift, a professor of petroleum geology at Louisiana State University, who was not involved in the research. “I think that a lot of that evidence is already in existence, and that the paper will be seen as something quite fundamental a few years in the future.”
Jagoutz said that based on literature printed in the 1970s and 1980s, most people assumed 40 million years ago was the right answer.
“Then somehow the literature went in another direction, and people largely forgot this possibility. Now this opens up a lot of new ideas," he added.