Scientists may have overthrew 100-year-old theories about what holds the highest mountain range on Earth, new research shows.
The Himalayas formed around 50 million years ago in a clash between Asia and the Indian continent, with tectonic forces choking Tibet hard, causing the region to crumpled, shrinking its area almost 620 miles (1,000 km). The Indian tectonic plate eventually slipped under the Eurasian plate, doubling the thickness of the Earth’s crust below the Himalayas and Tibetan plateaus north, contributing to its uplift.
For a century, this leather doubled was a common theory that it carried the weight of the Himalayas and Tibetan Plateau. A study published in 1924 by Swiss geologist Emile Agand shows that Indian and Asian crusts stacked on one another, extending to a depth of 45-50 miles (70-80 km) below the surface of the Earth.
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However, this theory cannot withstand scrutiny, as researchers now turn the rocks in the crust to melt about 25 miles (40 km) deep due to extreme temperatures.
“If you have a crust of 70 km, the bottom is ductile… it becomes like yogurt. And you can’t build a mountain on top of yogurt,” says Pietro Stelnai, an associate professor of geophysics at the University of Bicocca in Italy and the lead author of a new study that analyzed geologies under science.
The evidence has long suggested that Anand’s theory is false, but the idea of two neatly stacked crusts is very appealing, and most geologists have not questioned it, Stellnay said. Historically, “all of the data coming will be interpreted in terms of a single, double-thick crustal layer,” he said.
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However, new research reveals that there is a mantle sandwiched between the crusts of Asia and India. This explains why the Himalayas have become so tall and why they remain so high today, the author wrote on paper.
The mantle is the layer of the earth directly beneath the earth’s crust. It is much more dense than the crust and therefore does not liquefy at the same temperature. The crust, on the other hand, is very light and buoyant, so it behaves like an iceberg, with the thicker it lifting up above the surface of the Earth.
Stellnai and his colleagues discovered a mantle insert by simulating a collision between the Asian and Indian continents on a computer. This model showed that when Indian plates began to slide down and liquefy underneath the Eurasian plates, the mass rose and adhered not to the bottom of the Asian crust but to the base of the lithosphere, the hard outer layer of the planet made up of the crust and upper larch.
This is fundamental, Sternai means there is a hard layer of mantle between the stacked crusts that solidify the entire structure beneath the Himalayas. The two crusts provide sufficient buoyancy to keep the area lifted, and the mantle material provides resistance and mechanical strength. “We have all the materials needed to increase the terrain and maintain the weight of the Himalayas and Tibetan Plateau,” he said.
The researchers then compared the results with seismic data and information collected directly from the rocks. The mantle sandwiches in the simulation were consistent with previous evidence that Anand’s theory could not be explained, Simone Pilia, an assistant professor of geoscience at Kingfahl University, Petroleum University and Minerals in Saudi Arabia, told Live Science.
“Things actually make sense,” Pilia said. “The supposedly enigmatic observations are actually explained more simply by having a model with a crust, mantle and crust.”
Although this study presents strong evidence for this model, it is controversial to Arnaud’s 100-year-old theory, as it is so widely adopted, Pilia said.
“The authors think it’s right that this is controversial,” Adam Smith, a postdoctoral researcher at the University of Glasgow in Scotland who was not involved in the study, told Live Science in an email. “All previous jobs generally agreed that all the materials under the Himalayas came from the crust.”
But the results are still plausible and explain the geological oddities of many of the Himalayas, Smith said. “The author runs many simulations using different thicknesses for every layer, and appears to always pinch this mantle between the crusts of two plates.”
Duwe van Hinsbergen, a professor of global tectonics and paleogeography at Utrecht University in the Netherlands, was not involved in the study, but opposed the controversial results. “It’s a great new discovery and an elegant interpretation,” he told Live Science in an email. “When a continent pushes under another continent, we expect a sandwich that consists of the mantle lithosphere of the upper (Tibetan) plate and the crust of the lower (Indian) plate from the top to bottom of the crust.”
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