The geology that holds up the Himalayas is not what we thought, scientists discover
Scientists may have reversed a 100-year-old theory of what maintains the highest mountain range on earth, according to new research.
The Himalayan mountains were formed in the collision between Asian and Indian continents about 50 million years ago, when tectonic forces Tibet tight so strong that the region collapsed and its area decreased by almost 620 miles (1,000 kilometers). The Indian tectonic plate finally slipped under the Eurasian plate, doubling the thickness of the earth’s crust under the Himalayas and the Tibetan plateau to the north, and contributing to their uprising.
For a century, the dominant theory was that this doubling of the crust alone carries the weight of the Himalayas and the Tibetan plateau. Research Published in 1924 by the Swiss geologist Émile Argand shows the Indian and Asian crusts stacked on each other, extending together from 45 to 50 miles (70 to 80 km) deep below the surface of the earth.
But this theory does not resist the exam, the researchers now say, because the rocks of the crust become melted about 25 miles (40 km) deep due to extreme temperatures.
“If you have 70 km of crust, then the lowest part becomes ductile … it becomes like yogurt – and you cannot build a mountain above yogurt,” Pietro SternaiAssociate professor of geophysics at the University of Milan-Bicocca in Italy and the main author of a new study analyzing geology under the Himalayas, told Live Science.
The evidence has long suggested that Arnand’s theory is wrong, but the idea of two carefully stacked crusts is so attractive that most geologists have not questioned it, said Sternai. Historically, “all of the data that would happen would be interpreted in terms of a double thickness crustal layer,” he said.
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However, the new study reveals that there is a piece of coat sandwich between Asian and Indian crusts. This explains why the Himalayas have become so large and how they remain so high today, the authors wrote in the article, published on August 26 in the journal Tectonic.
The coat is the layer of earth which is directly under the crust. It is much denser than the crust and, therefore, does not liquefy at the same temperatures. Meanwhile, the crust is so light and dynamic that it behaves similarly to an iceberg, lifting higher above the surface of the earth, the thicker it is.
Sternai and his colleagues discovered the coat insert by simulating the collision between Asian and Indian continents on a computer. The model showed that when the Indian plate slipped under the Eurasian plate and began to liquidate itself, stains of it rose and did not fix themselves at the bottom of the Asian crust, but at the base of the lithosphere, which is the rigid exterior layer of the planet composed of the crust and the upper coat.
This is fundamental, said Sternai, because it means that there is a rigid coat layer between the stacked crusts consolidating the entire structure under the Himalayas. The two crusts give enough buoyancy to keep the region lifted, while the material of the mantle ensures resistance and mechanical resistance. “You have all the ingredients you need to raise the topography and maintain the weight of the Himalayas and the Tibetan plateau,” he said.
The researchers then compared their results with the seismic data and the information collected directly from rocks. The mantle sandwich in the simulation corresponded to the previous evidence that Arnand’s theory could not explain, co-author of the study Simone PiliaDeputy professor of geoscience at the University of Petroleum and Minerals of King Fahd, Saudi Arabia, told Live Science.
“Things are starting to have a meaning now,” said Pilia. “The observations that seemed to be enigmatic are in fact more easily explained by having a model where you have the crust, the coat, the crust.”
The study presents solid evidence of this model, but contradicting the theory of 100 years of Arnaud is controversial because it was so largely adopted, said Pilia.
“I think the authors are right to say that it is controversial”, ” Adam SmithA postdoctoral research partner in digital modeling at the University of Glasgow in Scotland who was not involved in the study, said in Live Science in an email. “All previous work has generally agreed that all the equipment under the Himalayas came from the crust.”
But the results are always plausible, and they explain a number of geological quirks in the Himalayas, said Smith. “The authors manage many simulations using different thicknesses for all layers, and they always seem to get this little coat sandwich between the crust of the two plates.”
Douwe Van HinsbergenProfessor of global tectonics and paleogeography at the University of Utrecht in the Netherlands which was not involved in the study, did not agree that the results are controversial. “It is a new discovery and an elegant interpretation,” he told Live Science in an email. “If a continent grows under another continent, you expect a sandwich that consists from top to bottom of the crust and the lithosphere of the upper plate (Tibet), then the crust of the lower plate (Indian).”
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