Scientists studying a massive, 350-kilometer-wide hot zone deep beneath the northern part of the United States’ Appalachian Mountains, near New England, have determined that the mysterious region of deep heat is likely a remnant of the split between North America and Greenland that occurred over 80 million years ago.
Known as the Northern Appalachian Anomaly (NAA), the enigmatic hot zone, located 200 km beneath the surface, likely accounts for previously unexplained diamond-filled volcanic eruptions and other geological effects in the areas above the hot zone that have occurred over the millions of years since its formation.
Although previous theories have tied the NAA’s origin to plate tectonic movements resulting from the split between North America and North Africa over 180 million years ago, the new origin hypothesis offers the most complete explanation for all the hot zone’s observed characteristics, many of which have frustrated previous explanation efforts.
The research team behind the proposal stated that their research could enhance the understanding of the hot zone’s impact on contemporary environment and climate dynamics.
Mantle Wave Theory Could Explain Puzzling North Atlantic Anomaly Hot Zone
In a recent statement, Tom Gernon, a Professor of Earth Science at the University of Southampton and the lead author of the study detailing the team’s work, said the anomalous hot zone lies beneath a part of the North American continent that has been “tectonically quiet” for the last 180 million years.
“This thermal upwelling has long been a puzzling feature of North American geology,” Gernon said, before adding, “so the idea it was just a leftover from when the landmass broke apart never quite stacked up.”
In search of a better explanation for the mysterious hot zone, the Southampton professor explored the concept of the ‘mantle wave’ theory. According to the statement, the theory describes how the hot, dense rock found at these depths starts to peel away from the base of tectonic plates, “much like blobs in a lava lamp,” once the continents break apart.
Now free from the continental shelf, these blobs ripple along the lower surfaces of the continents like waves rippling on a pond. Based on geological observations and computer simulations, this process can occur over tens of millions of years. It’s this movement that the team believed caused the hot zone’s birth and migration under its current location.
The team’s previous research suggested the rock drips can line up in series like dominoes. When they fall, they effectively “migrate” over time.
Professor Sascha Brune, co-author of the study who leads the Geodynamic Modelling Section at GFZ in Potsdam, Germany, said the puzzling hot zone underneath the Appalachian Mountains is “very likely one of these drips, which originated far from where it now sits.”
Seismic and Tectonic Data Suggest Labrador Sea Origin 80 Million Years Ago
To support the hot zone formation theory, the team collected seismic tomography data, which uses sound waves to image the area beneath the Earth’s surface, previously captured in the area. By combining this data with tectonic plate reconstructions, the team created advanced computer simulations to approximate the formation of the NAA. According to the published results, the simulations suggest that the puzzling hot zone was likely formed sometime between 90 and 80 million years ago, roughly 1,800 kilometers from its present position, during the breakup of the Labrador Sea when Greenland separated from Canada.
While more research is needed to confirm the NAA origin theory, the team said their result suggesting it has slowly migrated across the lithosphere “at a rate of approximately 20 kilometers per million years. The team said this rate is “broadly consistent” with independent geodynamic predictions. They said the hot zone’s size and depth also “align closely” models designed to predict these types of “migrating instabilities.” If correct, the slow-moving anomaly should pass beneath the New York area sometime within the next 15 million years.
Gernon said a mantle wave origin would help explain extremely rare volcanic eruptions that can raise diamonds to the Earth’s surface. The theory would also account for the unusually high inland regions that don’t easily fit into other models.
“Our research suggests it’s part of a much larger, slow-moving process deep underground that could potentially help explain why mountain ranges like the Appalachians are still standing,” he explained. “Heat at the base of a continent can weaken and remove part of its dense root, making the continent lighter and more buoyant, like a hot air balloon rising after dropping its ballast.”
If correct, the Southampton professor said this increased buoyancy would have caused the ancient inland mountains “to be further uplifted” to their current heights over the next few million years.
Twinning is Winning? The NAA May Have a “Mirror Image” Sibling
In the same study, the research team suggests a similarly puzzling hot zone beneath north-central Greenland may have formed from the opposite flank of the Labrador Sea during the same event. If correct, the team said the two hot zones would be mirror images of each other, but moving in mostly opposite directions.
The team notes that previous studies have shown the hot zone beneath Greenland plays a role in heat flow at the base of the ice sheet, which is several kilometers thick, affecting the ice’s present-day melting rate and movement. Gernon said this hot zone effect is evidence that ancient heat anomalies, such as the NAA, “continue to play a key role in shaping the dynamics of continental ice sheets from below.”
“Even though the surface shows little sign of ongoing tectonics, deep below, the consequences of ancient rifting are still playing out,” he added. “The legacy of continental breakup on other parts of the Earth system may well be far more pervasive and long-lived than we previously realised.”
Along with melting and moving ice, the researchers said these instabilities can also continue to shape regional uplift and patterns of volcanism and erosion, “even across parts of the continental interiors previously thought to be geologically stable.”
Dr Derek Keir, study co-author and tectonics expert at the University of Southampton and the University of Florence, said the proposal that the “rifting of continents” can cause deep masses of circulating hot rock spread thousands of kilometres inland “makes us rethink what we know about the edges of continents both today and in Earth’s deep past.”
The study “A viable Labrador Sea rifting origin of the Northern Appalachian and related seismic anomalies” was published in Geology.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.