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Himalayas formation may have destroyed at least 30% of continental crust in collision zone
https://phys.org/news/2024-11-himalayas-formation-destroyed-continental-crust.html [phys.org]
Earth's continents are slowly moving across the planet's surface due to plate tectonics, culminating in regions of crustal expansion and collision. 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. Furthermore, when two continental plates collide, distinct topographic features are produced, namely mountain ranges, which are surficial manifests of Earth's thickened crust.
Three such collision zones form the Himalaya-Tibetan Plateau, the European Alps and the Zagros Mountains in Iran, Iraq and Turkey, originating during the Cenozoic (last 66 million years). New research, published in Earth and Planetary Science Letters, has attempted to quantify the amount of continental crust lost to the mantle when two plates collide at each of these boundaries.
To do so, Dr. Ziyi Zhu, Research Fellow at Monash University, Australia, and colleagues developed a theoretical model for the mass/volume balance of continental crust and compared the amount of shortened crust with the crust being vertically thickened, laterally extruded and eroded at the surface.
Simplifying the utility of each of these parameters in the calculations, Dr. Zhu says, "Imagine squeezing a soft chocolate bar: the material compressed (horizontal shortening) forms a pile (vertical thickening).
"Additionally, the crust can move in directions perpendicular to the compression (extrusion) or undergo erosion. If crustal mass is conserved, the mass of the shortened crust should balance with the mass of the thickened crust, along with any crust lost to erosion or lateral extrusion. Any imbalance indicates that the missing crust likely sinks into the mantle."
The research team identified that at least 30% of continental crust was lost to the mantle during the formation of the Himalaya-Tibetan Plateau and Zagros Mountains (potentially up to 64% for the latter, depending upon the initial crust thickness), while up to 50% of the Alps' volume may have been destroyed. Importantly, this loss to the mantle had double the destructive effect than that of surface erosion, which is estimated based on the volumes of sediment fans associated with each mountain range.
