The fate of the sinking tectonic plates revealed
AUSTIN, Texas – The surface of our world is a jumble of tectonic plates jostling each other, new ones emerge as others are dragged along. The current cycle keeps our continents in motion and animates life on Earth. But what happens when a plaque disappears inside the planet?
The question has puzzled scientists for a long time because conventional wisdom said that sinking tectonic plates must remain intact to continue shooting the part behind them, but according to geophysical evidence, they are destroyed.
Now, in a study published on November 11 in Nature, scientists say they have found an answer that reconciles the two stories: the plates are considerably weakened when they sink, but not to the point of separating completely.
The discovery came after scientists passed tectonic plates through a computer-generated glove of destructive geological forces. The model showed that when the plate penetrates the mantle, it sharply bends downward, cracking its cold, brittle back. At the same time, bending changes the fine-grained structure of the rock along its belly, leaving it weakened. Combined, the stresses pinch the plate along its weak points, leaving it largely intact but segmented like a soft snake.
This means that the plate continues to be pulled down even though it is bent and warped.
According to the researchers, the model predicted a scenario that matches Japan’s observations. Studies of the region where the Pacific tectonic plate plunges – or subducts – beneath Japan have revealed large cracks where the plate bends downward, and they have shown signs of weaker material below. Deep seismic imaging conducted by the University of Texas at Steve Grand of Austin also revealed tectonic shapes in the Earth’s mantle beneath Japan that appear to closely match the model’s slinky snake.
Co-author Thorsten Becker, a professor at UT’s Jackson School of Geosciences, said the study doesn’t necessarily end the book on what happens to subduction plates, but it certainly gives a compelling argument to explain several important geological processes.
“This is an example of the power of computational geoscience,” said Becker, who helped develop the model and is also a researcher at UT’s Oden Institute for Engineering and Computer Sciences. “We combined these two processes that geology and rock mechanics tell us to happen, and we learned something about the general physics of how the Earth works that we weren’t expecting. As a physicist, I find this exciting.
Lead author of the study, Taras Gerya, professor of geophysics at ETH Zurich, added that so far geophysicists have not fully explained how tectonic plates bend without breaking.
Things got interesting when the researchers ran their simulations with a warmer interior, similar to that of early Earth. In these simulations, the tectonic snake segments only reached a few kilometers in the mantle before breaking up. This means that the subduction would have occurred intermittently, raising the possibility that modern plate tectonics did not begin until the last billion years.
“Personally, I think there are a lot of good arguments for plate tectonics to be much older,” Becker said, “but the mechanism revealed by our model suggests things might be more temperature sensitive. mantle than we thought, and that, I think it could lead to some interesting new avenues for discussion.
Becker and Gerya were joined by David Bercovici, a geophysicist at Yale University whose investigation of how rock grains are weathered in the deep mantle helped motivate the research. The study is based on a two-dimensional computer model of plate tectonics incorporating Bercovici’s research on rock deformation and other plate weakening mechanisms. Researchers are now studying the phenomena using 3D models and plan to study what these models can tell them about the occurrence of earthquakes.
The research was funded by grants from the Swiss National Science Foundation, ETH Zurich and the United States National Science Foundation. The simulations were carried out on high performance computing clusters at ETH Zurich.