Find the lost lithosphere millions of years ago

Geographers at the University of Illinois at Urbana-Champaign have identified the location of a massive mass of earthy lithosphere 15 million years ago. Thanks to the discovery of a huge rock beneath Tibet 'long-standing hidden ', the way scientists have contributed to solving a long-standing mystery, and clarifying how the continents operate when they collide.

The Tibetan Plateau and the adjacent Himalayan Mountains are created by the movement of large tectonic plates, which include the outer layer of the earth, or lithosphere. About 55 million years ago, the Indian disk hit the Eurasian plate, pushing the ground slowly downward and rising. With an area of ​​nearly one tenth of the United States and an average altitude of 16,000 feet above sea level, Tibet Plateau is the largest and highest plateau in the world.

The stratigraphic models of Tibet vary greatly, with concepts such as the Eurasian disk moving process, the Indian disk movement process, and the thickening of the Eurasian lithosphere. According to the latest model, this thick layer of lithosphere becomes unstable, and a block of lithosphere has broken and sunk deep into the mantle layer in the earth. (Mantle is located in the middle of the earth and the core, within 33km - 2,900km, accounting for 83.3% of the Earth's volume. Because it is in the middle, it is also called an intermediate layer.)

'While in it, the giant lithosphere in the mantle layer below Tibet acts as an anchor, anchoring the upper part in one place,' said Wang-Ping Chen, university geophysics professor. Illinois said. 'Then about 15 million years ago, the chain broke and the ground rose, rising and becoming the highest plateau.'

And until recently, this tantalizing theory still lacks a clear proof to prove it. But then, Dr. Tai-Lin (Ellen) Tseng and Professor Chen discovered the lost anchor.

"This leftover lithosphere has provided a key evidence for demonstrating a direct link between continental collisions near the surface and underground dynamics in the mantle class," Tseng said.

'In addition, fundamentally, mantle motivation also accelerates stratigraphic activity, so the fate of the lithosphere in the mantle layer below Tibet is the basis for understanding the full dynamics of the collision " .

Through a project called Hi-CLIMB - a comprehensive study of the Tibetan-Himalayan Earthstone during the formation of the mountain, Tseng analyzed seismic signals, collected from many fixed stations. and temporarily, to find this missing lithosphere.

The Hi-CLIMB project builds a series of seismic monitoring stations, stretching from the Indian plains, through Nepal, across the Himalayas to central Tibet. 'With the deployment of more than 200 stations, the Hi-CLIMB project is the most extensive broadband project ever made,' said Professor Chen, one of the project's two key researchers.

Using the seismic information obtained from many stations, Ms. Tseng accurately measured the velocity of seismic waves moving below the area with a depth of 300 to 700 km. Because the more cold the rock is, the faster the seismic wave moves through it, so from her data, Ms. Tseng can recognize the locations of the cold lithosphere that are separate. 'We not only discovered the missing cold lithosphere, but also reconstructed the geological disk location 15 million years ago,' said Tseng. 'So it is very likely that the volatility in the lithosphere is more and more a part of the formation of the Tibetan plateau, rather than the large-scale movement of one of the Geological disc. "

The two scientists said other evidence, including the age and distribution of volcanic rocks and the perception of the current background movement in Tibet, also revealed that the remaining lithosphere, lost, was lost. 15 million years ago.

Thanh Van