A fascinating new study reveals that a massive chunk of Earth’s crust, buried deep beneath the Midwest, is slowly pulling large parts of North America’s crust into the Earth’s mantle. This process, described as “dripping,” occurs due to the lingering effects of an ancient tectonic plate known as the Farallon plate.
The Farallon Slab and Its Impact on North America
The study published in Nature Geoscience, led by geoscientist Junlin Hua, points to the Farallon slab, a segment of oceanic crust that broke off from the main tectonic plate millions of years ago. This ancient slab, once part of a subduction zone along the continent’s west coast, continues to influence the region beneath North America.
According to Hua, the Farallon slab is responsible for “cratonic thinning” beneath the Midwest, where the crust is slowly being pulled down into the mantle. The influence of the slab extends across a broad region, from Michigan to Nebraska and Alabama.
The seismic mapping revealed large “drips” hanging from the underside of the North American continent, extending roughly 400 miles (640 kilometers) into the Earth’s mantle. These drips create a funnel-like structure, drawing material from across the continent toward the region beneath the slab before it is sucked down into the mantle.
Groundbreaking Seismic Imaging Uncovers Hidden Forces
To uncover this hidden phenomenon, the research team utilized a groundbreaking seismic imaging method known as full-waveform inversion. This advanced technique allowed scientists to capture a detailed view of the Earth’s interior, specifically the mantle and crust beneath North America.
Full-waveform inversion analyzes seismic waves from earthquakes to extract information about the physical properties of the Earth’s layers, helping to visualize the forces at play deep below the surface.
The study’s findings suggest that, for the first time, researchers have been able to observe cratonic thinning as it happens. This discovery provides a valuable glimpse into how the Earth’s crust changes over geologic timescales.
A Peek Into Earth’s Deep Geological Past
The Farallon plate’s influence on North America dates back to roughly 20 million years ago when the plate began breaking apart due to the advancing Pacific plate. Over time, pieces of the Farallon plate slowly sank into the Earth’s mantle, leading to the phenomena seen today.
The slab, which lies at the boundary between the mantle transition zone and the lower mantle, was first imaged in the 1990s but its full impact on the North American plate has only recently been understood.
Researchers believe that the “dripping” effect seen beneath the Midwest will not lead to any immediate changes on the Earth’s surface. As the Farallon slab sinks deeper into the mantle, its influence on the overlying crust will likely diminish, and the “dripping” may eventually stop.
Nevertheless, the discovery has opened the door to better understanding how continents are formed, broken apart, and recycled in the Earth’s deep geological processes.
Through these revelations, scientists are one step closer to answering fundamental questions about how Earth’s surface has evolved and continues to transform over millions of years.
