A groundbreaking study led by the University of Texas at Austin has revealed that parts of North America are slowly sinking into the Earth’s mantle a process researchers call “cratonic thinning.” The unusual geologic process is related to ancient tectonic forces that continue to shape the continent from deep below the surface.
By using advanced seismic imaging and geodynamic modeling, researchers discovered massive, drip-like formations accumulating beneath the central United States. The underground drips extend over 640 kilometers (400 miles) deep into the ground and encompass regions beneath Michigan, Nebraska, and Alabama.
Central to the phenomenon is the Farallon slab, an ancient oceanic plate that began subduction beneath North America over 100 million years ago. Although removed from the surface centuries ago, remnants of the slab are ongoingly sinking into the lower mantle, generating deep mantle flow that is depleting the overlying lithosphere. This is causing chunks of Earth’s outer layer to gradually “drip” downward into the mantle transition zone.
“This is the first time we’ve possibly caught cratonic thinning in action,” said lead author Junlin Hua, who began the study as a postdoctoral researcher at UT’s Jackson School of Geosciences. Now a professor in China, Hua emphasized that the discovery gives scientists a rare glimpse into how continents evolve from within.
The study suggests that a wide funnel-shaped region below the Midwest is drawing rocks from across North America toward it, horizontally drawing material into the zone of dripping where it eventually rests. This gradual but relentless process is slowly wearing away the continent’s ancient geologic core, the craton, at its base.
While the discovery sounds foreboding, researchers stress that there is no imminent danger to the surface. The movements are occurring over millions of years and will not impact landscapes or ecosystems visibly in the near term. Eventually, the dripping should stop as the Farallon remnants dissipate.
It shows us how continents are constructed, destroyed, and recycled back into the Earth,” explained co-author Thorsten Becker. The scientists also used information from the EarthScope project to allow them to build a high-resolution tomographic image of the crust and mantle beneath North America.
The study is published in Nature Geoscience and is a major step towards unlocking the Earth’s deep inner workings.
