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Mystery of the Tibetan Plateau Solved: Study Finds the Strength of Tectonic Plates Caused its Unique Shape

Jul 25, 2017

Researchers have discovered the Tibetan Plateau's shape, which dwarfs other mountain ranges in height and breadth, may be controlled mostly by the strength of the tectonic plates whose collision prompted its uplift.While most mountain ranges appear like narrow scars of raised flesh, the Tibetan Plateau, formed by the convergence of the Indian and Asian tectonic plates, looks like a broad, asymmetrical scab surrounded by craggy peaks.According to a model developed by the researchers, the Tibetan Plateau's shape may be due to the Asian plate having a strong western side and weak eastern side.

A topographic map of the area around the Tibetan Plateau, left, and map view of the composite strong and weak Asian plate model, right. The composite model - with the Asian plate stronger in the west and weaker to the east - results in a topography similar to what is seen today
According to researchers at The University of Illinois at Urbana-Champaign, the Tibet region is one of the most seismically active areas in the world, so understanding the plateau's geologic history could give scientists insight to modern day earthquake activity,'The asymmetric shape and complex subsurface structure of the Tibetan Plateau make its formation one of the most significant outstanding questions in the study of plate tectonics today,' said University of Illinois geology professor and study co-author Dr Lijun Liu.
In the classic model of how the Tibetan Plateau formed, a rapidly moving Indian tectonic plate collided head-on with a mostly stationary Asian tectonic plate approximately 50 million years ago.This collision is likely to have caused Earth's crust to bunch up into a massive pile - known as the Himalaya Mountains and Tibetan Plateau seen today.

Natural-color satellite image of the Tibetan Plateau. While most mountain ranges appear like narrow scars of raised flesh, the Tibetan Plateau, formed by the convergence of the Indian and Asian tectonic plates, looks like a broad, asymmetrical scab surrounded by craggy peaks 

However, this model still doesn't explain why the plateau is asymmetrical, says Dr Liu. 'The Tibetan Plateau is not uniformly wide,' said Dr Lin Chen, the study's lead author from the Chinese Academy of Sciences.

'The western side is very narrow and the eastern side is very broad - something that many past models have failed to explain.'

Many of those past models have focused on the surface geology of the actual plateau region, Dr Liu said, but an explanation may be found further down, where the Asian and Indian plates meet.

'There is a huge change in topography on the plateau, or the Asian plate, while the landform and moving speed of the Indian plate along the collision zone are essentially the same from west to east,' Liu said.

'Why does the Asian plate vary so much?'

In order to answer this question, the researchers developed models of what happens when tectonic plates made from rocks of different strengths collide.

They used a series of 3-D computational continental collision models to test their ideas.

'We looked at two scenarios - a weak Asian plate and a strong Asian plate,' said Dr Liu.

'We kept the incoming Indian plate strong in both models.'

When the researchers ran the models, they found that the strong strong Asian scenario plate led to a narrow plateau, but the weak Asian plate model led to a broad plateau, like what is observed today.

A graphic showing how mountain ranges form. While most mountain ranges appear like narrow scars of raised flesh, the Tibetan Plateau, formed by the convergence of the Indian and Asian tectonic plates, looks like a broad, asymmetrical scab surrounded by craggy peaks 

 'We then ran a third scenario which is a composite of the strong and weak Asian plate models,' said Dr Liu.

'An Asian plate with a strong western side and weak eastern side results in an orientation very similar to what we see today.'

Tibetan Buddhist stupa and houses outside the town of Ngawa, on the Tibetan Plateau. According to a model developed by researchers, the Tibetan Plateau's shape may be due to the Asian plate having a strong western side and weak eastern side 

The researchers say that this model, besides predicting surface topography, also explains some of the complex subsurface structures using seismic observation techniques.

'It is exciting to see that such a simple model leads to something close to what we observe today,' Dr Liu said.

'The location of modern earthquake activity and land movement corresponds to what we predict with the model, as well.' (Daily Mail)

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