Study has shown that subduction zones are where tectonic plates sink into the earth’s mantle, and they bend, creating segments ‘like an eel’.
For the largest part, the motion of Earth’s plates is driven by the weight of cold, dense ocean crust sinking into the mantle — dragging the rest of the plate behind it.
Logically, subducting slabs must remain intact as they descend into the mantle, else they would be unable to keep pulling along the attached crust.
Geophysical evidence indicates that the plates may have been destroyed.
The findings by researchers led from ETH Zürich has reconciled these two hypotheses by showing that plates are only significantly weakened as they sink.
This conclusion was reached by the team after running simulations on computers to determine the effect of various geological forces upon subducting crust.
Until now, the researchers said, geophysicists have lacked a comprehensive explanation for how Earth’s tectonic plates bend without breaking.
A study concluded that tectonic plates become curved as they fall into the mantle at subduction zones. They then fragment ‘like an slinky serpent’. Pictured is the model by the researchers of viscosity (left), and grain size(right) for a five-mile (8 km) slab of subducting Oceanic crust.
In their study, geophysicist Taras Gerya of ETH Zürich and his colleagues developed a 2D model of plate tectonics that incorporated various plate-weakening mechanics, including data on how rock grains are altered in the deep mantle.
The model revealed that as plates enter the mantle it is abruptly bent downwards — causing its cold, brittle back to crack as the fine-scale grain structure along its underbelly changed, leaving it weakened.
Together, these cause the plate the pinch at its weak points, leaving it intact but nevertheless segmented — much like a ‘slinky snake’.
The descending slab will continue to pull on the rest of your plate without becoming bent or folded.
While the study has far from closed the book on what happens to tectonic plates when they subduct into the mantle, it does proving a compelling explanation of several important geological process, explained paper author Thorsten Becker.
The University of Texas at Austin geophysicist stated that “it’s an instance of the power of computation geosciences,”
‘We combined these two processes that geology and rock mechanics are telling us are happening, and we learned something about the general physics of how the Earth works that we wouldn’t have expected.
“As an physicist I find that fascinating,” he said.
They also tried running simulations using a hotter material to simulate the conditions found in early Earth.
Under these circumstances, the snake-like tectonic segments only succeeded it making it a few miles into the mantle before breaking off — suggesting that subduction may have only occurred intermittently.
According to the team, this suggests that plate tectonics may have only begun in the last few billion years.
The researchers claim that their model (left), which they developed, predicted an outcome similar to observations about the Pacific plate subsiding beneath Japan (right). Studies have shown large cracks in the plate where it bends downwards — alongside evidence for weaker material on the plate’s underside
Professor Becker cautioned, “Personally I believe there are many good arguments for platetectonics to be much older.”
“But, the mechanism shown by our model suggests that things may be more sensitive than we think to temperature changes in the mantle.”
He concluded, “That, I believe, could lead to fascinating new avenues for discussion,”
The researchers have completed their initial research and are moving on to studying the exact same phenomena in 3D.
Nature published the full results of this study.
Earth moves under our feet. As tectonic plates scrape against one another, they move through the mantle.
The mantle’s uppermost layer and Earth’s crust make up the tectonic plate.
Below, you’ll find the asthenosphere. It is the warm, viscous conveyor belt made of rock upon which tectonic plates move.
Earth’s fifteen tectonic plate (pictured) have shaped the terrain we see today.
Earthquakes occur near the edges of tectonic plates. This is when one plate falls below another and thrusts another upward or scrapes alongside each other.
Although earthquakes rarely happen in the center of plates, they may occur when faults and rifts deep below the surface are reactivated.
They are weaker than the rest of the plate and could easily slide and trigger an earthquake.