Devastating creation: The rise of the Himalayas has obliterated one-third of the Earth's continental crust (photo).

The continents of the Earth are far from static and slowly move across the surface of the planet, driven by plate tectonics, culminating in areas of expansion and collision of the crust. In the latter case, high temperatures and pressures lead to the reworking of the crust, affecting its composition as well as that of the underlying mantle. Additionally, during the collision of continental plates, various topographical features are formed, such as mountain ranges, as noted by PHYS.org.

It is important to highlight that mountain ranges are surface manifestations of thickened crust on Earth. Three such collision zones give rise to the Himalayan-Tibetan Plateau, the European Alps, and the Zagros Mountains in Iran, Iraq, and Turkey, which formed during the Cenozoic — over the last 66 million years. In a new study, researchers have attempted for the first time to quantitatively assess the amount of continental crust lost into the Earth's mantle when two plates collide at their boundaries.

The study was conducted under the leadership of Dr. Ziyi Zhu, a research fellow at Monash University in Australia. The team developed a theoretical model of the mass and volume balance of the continental crust and then compared the amount of shortened crust with that which thickens vertically. During this process, the crust is pushed sideways and eroded at the surface.

According to the scientists, the continental crust can move in several ways: perpendicularly to compression, known as extrusion, and can also undergo erosion. If the mass of the crust is conserved, the mass of the shortened crust must be balanced by the mass of the thickened crust or any crust lost due to erosion or lateral extrusion. Any imbalance indicates that the missing crust is likely sinking into the Earth's mantle.

The results of the study suggest that at least 30% of the continental crust was lost to the mantle during the formation of the Himalayan-Tibetan Plateau and the Zagros Mountains. Moreover, the scientists believe that losses could potentially reach a record 64%. Furthermore, the results indicate that up to 50% of the volume of the Alps may have actually been destroyed.

The researchers also believe that this loss to the mantle has had a significantly more destructive effect than surface erosion. According to Dr. Zhu, their work is important for several reasons. Firstly, the scientists have quantitatively determined for the first time the losses of the Earth's crust to the mantle during continental collisions. Secondly, the results suggest that the erosion of the massive Himalayan mountains created the largest and second-largest sediment cones on Earth — the Bengal and Indus cones. However, it is now known that the losses of crust to the mantle were in fact much greater.

The scientists suggest that the reworking of the crust during the formation of the Himalayan-Tibetan Plateau is likely driven by a delamination mechanism. This process involves several phases:

• rapid sinking or separation of the lower continental lithosphere;
• formation of potassium-adakitic rocks;
• delamination of the roots of the mountains.

A key consequence of the delamination of dense mountain roots is the rapid uplift of the mountain range above. The results indicate that the rapid uplift of the Himalayas, triggered by delamination, corresponds to the age of the potassium-adakitic rocks and coincides with the onset of intensified monsoon rains around 22 million years ago.

The authors of the study also note that their findings highlight the connection between deep processes in the Earth's crust and climate change at the surface during the formation of mountain belts through continental collision.