Ancient Rift With Greenland Still Heating the U.S. From Below

A vast zone of hot rock buried deep beneath the Appalachian Mountains may owe its origins not to ancient African tectonics, as once thought, but to the dramatic split between Greenland and North America nearly 80 million years ago, scientists report.

The thermal upwelling, known as the Northern Appalachian Anomaly (NAA), appears to be a slow-moving legacy of that rifting event, now sitting far from its birthplace beneath the northeastern United States.

This new perspective reshapes long-held assumptions about one of North America’s most puzzling geological features. The anomaly lies beneath a tectonically quiet region, and its heat and depth have defied easy explanation — until now.

A Slow-Motion Journey From the Labrador Sea

According to researchers from the University of Southampton, Germany’s GFZ Helmholtz Centre, and the University of Florence, the NAA likely began forming when Greenland began to drift from Canada, creating the Labrador Sea. At the time, hot unstable rock began peeling from the base of the Earth’s lithosphere.

Over millions of years, that instability — a kind of “drip” of hot rock — migrated southwestward across the continental plate, covering nearly 1,800 kilometers. It moved at a pace of about 20 km per million years and now lies 200 km below the Appalachian Mountains.

“This thermal upwelling has long been a puzzling feature of North American geology,” said Tom Gernon, lead author and professor of Earth Science at the University of Southampton. “It lies beneath part of the continent that’s been tectonically quiet for 180 million years, so the idea it was just a leftover from when the landmass broke apart never quite stacked up.”

The Mantle Wave Theory

To explain this kind of geologic movement, the team turned to a new idea they recently proposed: mantle wave theory. The concept likens Earth’s deep mantle to a lava lamp, where dense rock blobs peel away and ripple under tectonic plates for tens of millions of years.

“Heat at the base of a continent can weaken and remove part of its dense root, making the continent lighter and more buoyant,” Gernon explained. “Like a hot air balloon rising after dropping its ballast, this would have caused the ancient mountains to be further uplifted over the past few million years.”

Using geodynamic simulations and seismic tomography — essentially Earth-imaging using seismic waves — the scientists traced the NAA’s path back to the Labrador Sea rift zone, placing its origin between 90 and 80 million years ago.

Key Findings From the Study

– The Northern Appalachian Anomaly likely originated 1,800 km to the northeast near the Labrador Sea
– It has migrated at roughly 20 km per million years, now residing beneath New England
– The hot zone is about 350 km wide and sits 200 km below the surface
– A mirror image anomaly beneath Greenland likely shares the same rifting origin
– This deep heat may still be uplifting the Appalachian Mountains today

A Twin Anomaly Beneath Greenland

A similar zone of hot rock beneath north-central Greenland may be the NAA’s long-lost twin. The researchers believe it also emerged from the Labrador Sea breakup, but on the opposite flank.

That thermal anomaly could be influencing the Greenland Ice Sheet from below, altering how it moves and melts. As Gernon put it, “Ancient heat anomalies continue to play a key role in shaping the dynamics of continental ice sheets from below.”

Rethinking Continental Stability

Dr Derek Keir, a co-author from the University of Southampton and the University of Florence, emphasized the broader implications: “The idea that rifting of continents can cause drips and cells of circulating hot rock at depth that spread thousands of kilometres inland makes us rethink what we know about the edges of continents both today and in Earth’s deep past.”

Seemingly stable land masses may still be shaped by ancient breakups deep beneath the surface.

Even though the Appalachian region shows no active tectonic activity today, the lingering heat from ancient rifting may still be quietly influencing its topography. According to Gernon, “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.”

Reference

Journal: Geology
DOI: 10.1130/G53588.1
Article Title: A viable Labrador Sea rifting origin of the Northern Appalachian and related seismic anomalies
Authors: Thomas M. Gernon, Sascha Brune, Thea K. Hincks, Derek Keir
Publication Date: July 30, 2025

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