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Himalayan collision more recent than thought.

Researchers at the Massachusetts Institute of Technology have found evidence that the collision between India and Asia, which led to the formation of the Himalaya, occurred ten million years later than previously thought.

A team led by Oliver Jagoutz analysed samples from three tonnes of rock collected in the northwestern corner of the Himalaya, a region of Pakistan and India called the Kohistan-Ladakh Arc. The researchers collected more than 3,000 zircon crystals from the rocks and determined their age using isotope analysis. They then used further isotope analysis to determine the presence of a collision.

The results showed a clear signature: rocks older than 50 million years from both the northern and southern samples contained exactly the same ratio of isotopes. However, those younger than 50 million years from along the southern boundary of the arc 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 suggests that 50 million years ago, India collided with an island arc, pushing it northward. Ten million years later, India collided with the Eurasian plate, sandwiching the string of islands between the massive continents and forming the Kohistan-Ladakh Arc.

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Title Annotation:WORLDWATCH
Article Type:Brief article
Geographic Code:9INDI
Date:Apr 1, 2013
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