North America is 'dripping' blobs of rock down into Earth's mantle under the U.S.

Beneath the stable crust of North America, scientists have discovered something extraordinary: the deep roots of the continent are slowly dripping away in blobs of rock. 

This unusual geologic process appears to be driven by the remnants of an ancient tectonic plate, revealing a rare opportunity to observe “cratonic thinning” as it happens in real time. 

The phenomenon was identified by researchers at the University of Texas at Austin. Study lead author Junlin Hua conducted the research as a postdoctoral fellow at UT’s Jackson School of Geosciences.

“We made the observation that there could be something beneath the craton,” said Hua. “Luckily, we also got the new idea about what drives this thinning.”

How and why is North America dripping?

Cratons are ancient, stable rock formations that form the deep cores of continents. Some have remained relatively unchanged for billions of years. 

However, these formations are not immune to change. In rare cases, they lose parts of their structure, particularly their deepest root layers – a process known as cratonic thinning.

This thinning has been observed before in places like the North China Craton, which lost a substantial portion of its root millions of years ago. 

But what sets the new discovery apart is that the process is happening now, under the Midwestern United States, providing scientists with a live glimpse of how continents can subtly reshape from within.

Mantle dynamics and tectonic plates

Despite the striking nature of the discovery, researchers stress that there is no immediate threat to the surface landscape. The dripping occurs in the Earth’s mantle at a glacial pace, and over time it is expected to taper off. 

The process is driven by mantle dynamics, which influence how tectonic plates evolve but do so on a timescale of millions of years. 

Eventually, the effect will fade as the driving force behind the thinning – an ancient tectonic plate – sinks deeper into the Earth.

Hidden legacy of the Farallon Plate

The research team attributes this geologic activity to the lingering presence of the Farallon Plate, a former oceanic plate that began subducting beneath North America roughly 200 million years ago. 

Although the remnants of the plate are now about 600 kilometers below the surface, the study suggests it still plays an active role in reshaping the continent above it.

Thorsten Becker is a co-author of the study and professor at the Jackson School’s Department of Earth and Planetary Sciences and Institute for Geophysics. 

“This sort of thing is important if we want to understand how a planet has evolved over a long time,” said Becker. “It helps us understand how do you make continents, how do you break them, and how do you recycle them [into the Earth.]”

Detailed insights into Earth’s interior 

The research stems from a broader seismic modeling project led by Hua, now a professor at the University of Science and Technology of China. 

The model uses a technique called full-waveform seismic tomography, which offers detailed insights into the Earth’s interior by analyzing how seismic waves travel through different materials. 

Developed with support from co-author Stephen Grand and his team, the model was built using seismic data from the EarthScope project.

“Because of the use of this full-waveform method, we have a better representation of that important zone between the deep mantle and the shallower lithosphere where we would expect to get clues on what’s happening with the lithosphere,” Becker said.

Visualizing the dripping of North America 

The high-resolution model allowed scientists to visualize the dripping rock formations for the first time and to trace their connection to the Farallon Plate. 

The experts believe the plate influences the flow of mantle material in a way that scrapes and weakens the underside of the North American craton. It may also release volatile substances that further degrade the craton’s stability.

Interestingly, although the dripping appears most concentrated in a specific area beneath the Midwest, the entire craton – which spans most of the United States and Canada – shows signs of thinning.

“A very broad range is experiencing some thinning,” Hua said.

Modeling the Earth drip

To test the mechanics of the process, the researchers built a dynamic computer simulation. When the Farallon Plate was included in the model, the craton’s base began to drip.

When the plate was removed, the dripping stopped – strong evidence linking the two phenomena.

Becker emphasized that while no model is perfect, the resemblance between the simulation and observed data suggests the researchers are on the right track. 

“You look at a model and say, ‘Is it real, are we overinterpreting the data or is it telling us something new about the Earth? But it does look like in many places that these blobs come and go, that it’s (showing us) a real thing.”

Why does any of this matter?

This discovery adds a new layer to scientists’ understanding of how continents evolve over geological time.

It demonstrates that even the most ancient and seemingly immutable structures beneath our feet are still subject to deep and hidden forces. 

As researchers continue to refine seismic imaging technologies and develop more detailed models of Earth’s interior, they may uncover even more about the dynamic processes shaping our planet from below.

The research is published in the journal Nature Geoscience.

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