Tech geology researcher’s team reveals Himalayan collision took millions of years longer than once thought
The Himalayan Mountains have been in the news recently for a sudden blizzard that trapped nearly 1,000 climbers in life-threatening conditions – but new research by a Tennessee Tech University geologist shows that it took multiple continental collisions over millions of years to form the massive mountain range.
Gourab Bhattacharya, assistant professor of minerology and petrology at Tech, recently participated in a multi-university expedition to the Indus Basin, a vast river system that runs from the Tibetan Plateau through northern India and into Pakistan.
This western Himalayan site is more than 1,000 miles from Mount Everest, but it offered an ideal natural laboratory to reconstruct the timing of the ancient collision.
“Our research shows that the Indian plate collided with the Asian plate in western India around 40 million years ago, whereas eastward in southern Tibet, earlier studies demonstrate that the same collision occurred between 50 and 60 million years ago – a difference of 10 to 20 million years,” Bhattacharya said.
By analyzing tiny mineral grains from ancient river sediments, Bhattacharya’s team was able to trace when material from India and Asia first began to mix.
Using a dating technique often called a “rock clock,” the team discovered that the plates collided in western India about 40 million years ago. That study revealed the time gap of up to 20 million years because previous studies conducted farther east in southern Tibet show that the same collision began between 50 to 60 million years ago.
Co-author Delores Robinson of the University of Alabama explained, “Before the collision, a volcanic island chain sat within the Tethys Ocean between India and Asia. Its role has long puzzled researchers trying to constrain the ages of collision in the Himalayan region.”
Although the Tethys Ocean no longer exists, it was once the ancient sea that separated the northern and southern landmasses before they shifted into their current positions. The island once in the middle of the Tethys was like a geological bookmark, a trapped remnant of crust that preserved evidence of how the collision unfolded.
As the Indian plate moved north into Asia, the island was pushed up, reformed and eventually became part of the Indus Basin sediments. So, by studying its rocks and fossils, geologists can see that different parts of it rose at different times.
The researchers’ findings helped them reconstruct the sequence of Himalayan uplift, supporting the idea that the mountains didn’t rise all at once – like a geological car crash – but in a staggered, step-by-step way, with a series of slow impacts across different regions. Geologists call this a diachronous continent-continent collision.
Bhattacharya said, “Diachronous continent-continent collisions appear to be the rule, not the exception.”
He pointed out that North America experienced a similar long and drawn-out collision during a different geological period.
Co-author Jeff Benowitz, a geochronologist at the University of Colorado, Boulder, said, “It really shouldn’t surprise us that collisions between massive landmasses are drawn out in time. No continental margin is a perfectly straight line.”
See Bhattacharya’s full research findings published in Tectonics, an American Geophysical Union (AGU) journal, here.