Importance Score: 75 / 100 🔴
A groundbreaking geological study reveals that an ancient section of Earth’s crust, positioned deep under the American Midwest, is actively drawing significant portions of the present-day North American crust into the mantle. This newly observed phenomenon of cratonic thinning, driven by a deep-seated geological process, is reshaping our comprehension of continental evolution and mantle dynamics.
Massive ‘Drips’ of North American Crust Descending into Earth’s Mantle
Researchers have discovered that the immense gravitational pull of this subterranean slab is generating colossal “drips” extending from the base of the North American continent, plunging approximately 400 miles (640 kilometers) into the planet’s mantle. These substantial drips are situated beneath a region stretching from Michigan to Nebraska and Alabama, and their influence appears to extend across the entire continental landmass.
The area experiencing this downward pull resembles a vast funnel, where geological material from across North America is being drawn inwards horizontally before being pulled into the depths. Scientists observed that extensive regions of North America are losing material from the lower boundary of their crust due to this mantle suction.
Continental Thinning: A Widespread Phenomenon
“A remarkably wide area is undergoing crustal thinning,” stated Junlin Hua, the lead author of the study and a geoscientist who conducted this research as a postdoctoral fellow at The University of Texas (UT) at Austin. “Fortunately, we have also gained new insights into the mechanism driving this phenomenon,” added Hua, who is now a professor at the University of Science and Technology of China.
The research team determined that these geological drips are a consequence of the downward force exerted by a fragment of oceanic crust that detached from an ancient tectonic plate known as the Farallon plate.
The Farallon Slab and its Deep Mantle Influence
Historically, the Farallon plate and the North American plate constituted a subduction zone along the western edge of the continent. In this zone, the Farallon plate was sliding beneath the North American plate, with its material being recycled into the mantle. Around 20 million years ago, the advance of the Pacific plate caused the Farallon plate to fracture, and remnant slabs subducted beneath the North American plate gradually drifted into deeper regions.
Currently, one of these slabs, termed the “Farallon slab,” is positioned at the boundary between the mantle transition zone and the lower mantle, approximately 410 miles (660 km) beneath the Midwest. First identified in the 1990s, this segment of oceanic crust is now understood to be the cause of “cratonic thinning,” as detailed in the new study published in the journal Nature Geoscience on March 28.
Unprecedented Observation of Cratonic Thinning
Cratonic thinning is defined as the gradual erosion of cratons, which are ancient, stable sections of Earth’s continental crust and upper mantle that have remained largely unchanged for billions of years. While cratons are known to be capable of undergoing modifications, observing this process in real-time has been impossible due to the vast timescales involved in geological change.
Now, for the first time, scientists have documented cratonic thinning as it occurs. This significant discovery was made possible through a broader research initiative, spearheaded by Hua, to map the subsurface structure of North America using a sophisticated seismic imaging technique known as “full-waveform inversion.” This advanced method utilizes various types of seismic waves to extract comprehensive data regarding underground physical properties.
Related Earth Science Discoveries
Further reading on related topics:
- — Earth’s Layers: Exploring our Planet Inside and Out
- — Scientists Accidentally Discover Earth’s Inner Core is Less Solid Than Expected
- — Scientists Discover ‘Sunken Worlds’ Hidden Deep Within Earth’s Mantle That Shouldn’t Be There
Understanding Planetary Evolution
“This type of research is crucial for understanding the long-term evolution of a planet,” commented study co-author Thorsten Becker, a distinguished chair in geophysics at UT Austin. “The application of the full-waveform method has provided us with a more refined depiction of the critical zone between the deep mantle and the shallower lithosphere, encompassing the crust and upper mantle.”
To validate their findings, the researchers employed computer modeling to simulate the effect of the Farallon slab on the overlying craton. The simulations demonstrated that a dripping zone emerged in the presence of the slab but disappeared when the slab was removed. This confirmed, at least theoretically, that a submerged slab can indeed drag geological material from a broad area down into Earth’s interior.
Long-Term Geological Processes
The ongoing dripping process beneath the Midwest is not expected to cause immediate surface changes, according to the researchers. They also suggest that this process may eventually cease as the Farallon slab descends further into the lower mantle, diminishing its influence on the craton above.
These discoveries contribute significantly to our understanding of the complex processes that have shaped Earth’s current structure. “It aids in deciphering how continents are formed, how they fragment, and how they are recycled over geological time,” Becker concluded.