Research figures showing rocks dripping from cratons. Researchers assume that the dropping is caused by the remains of the sinking Faralon Slab below the craton. Credits: Nature Geoscience, Hua et al.
Researchers have discovered that the underside of the North American continent drips down rock masses, and that the remains of tectonic plates sinking into the Earth’s mantle may be the reason.
A paper published in Nature Geoscience describes a phenomenon discovered at the University of Texas at Austin. This is the first time that “Cratonic Thin” has been run and captured.
“We made the observation that there could be something under the craton,” said Junlin Hua, the lead author of the study, who conducted the study during a postdoctoral fellowship at the Jackson School of Earth Sciences at UT. “We’re lucky enough to have a new idea about this thinner drive.”
Cratons are very old rocks that are part of the Earth’s continent. They are known for their stability and ability to last for billions of years. However, sometimes craton undergoes changes that can affect stability, or removes the entire rock formation.
For example, North China’s cratons lost their deepest roots millions of years ago.
Researchers say what makes the discovery of the kratonic drip special is that it is happening now. This allows scientists to observe the cratonic thinning process.
The drip is concentrated in the Midwest of the US. There’s no need to worry about the continent screaming or changing the landscape anytime soon, researchers assure us. The mantle process driving drip can affect how tectonic plates evolve over time, but they are very slow. Furthermore, it is expected that the drip will eventually cease as the tectonic plate remains sink deep into the mantle and the influence on the craton sinks.
The discovery is of paramount importance to geoscientists studying continents throughout their lifetimes, says co-author Thorsten Becker, a professor at the Department of Earth and Planetary Sciences and the Institute of Geophysics at Jackson School.
“This kind of thing is important if you want to understand how planets have evolved over a long period of time,” Becker said. “It helps us understand how we create continents, how we break them, how we recycle them (to Earth).”
Seismic waves pass through different geological features at different velocities. This map shows the seismic velocity of the Earth’s crust at 200 km deep in the US and parts of Central America and Canada. North American cratons (outlined by the black dash) have higher seismic speeds compared to their surroundings. Credit: Nature Geoscience (2025). doi:10.1038/s41561-025-01671-x
The dripping discovery comes from a large project led by Hua, a professor at the University of Science and Technology in China. This uses an approach developed by co-author Stephen Grand, who is now Professor Emelitas at Jackson School, and his team, to create a new full-wave seismic fault model in North America. Using seismic data collected by the EarthScope project, this computer model reveals new details about the geological processes taking place in the underlying crust and mantle in North America.
“Because this full-wave-format method is being used, it better represents that important zone between the deep mantle and shallow lithosphere, and we hope to get clues as to what’s going on with the lithosphere,” Becker said.
This model was the first time that drips were put into view using this method. Researchers also helped speculate that the Faralon Plate, an offshore tectonic plate that has subducted in North America for the past 200 million years, could drive the process despite being separated to about 600 kilometres from the craton.
The plates, first seismically imaged by the Grand in the 1990s, played an important role in shaping the plates in North America. Researchers believe that it is currently worn down from below on the continent by redirecting the flow of mantle material to shear the base of the craton, releasing volatile compounds that weaken the base.
The drip is concentrated in one area of the craton, but Hua said the plate appears to interact with the material of the craton, which covers most of the US and Canada.
“It’s a little thinner over a very wide area,” Hua said.
When researchers constructed a computer model of these dynamics, the model cratons were dripped in when the Faralon plate was present. Once the plate was removed the drip stopped.
Becker acknowledges that there are limitations to computer models. But it’s a good indication that it resembles the data from the model, he said.
“You looked at the model and said, ‘Is that true? Are we over-interpreting data, or can we tell you something new about the Earth?” Becker said.
Details: Junlin Hua et al, Slab-induced drip, seismic full-waveform tomography of active chratonic thinning under North America, consistent with Nature Geoscience (2025). doi:10.1038/s41561-025-01671-x
Provided by the University of Texas at Austin
Quote: North America is Dripping from Beneath, Earth Scientists Retrieved April 1, 2025 from https://phys.org/news/2025-04-north-america-geoscientists.html (April 1, 2025)
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