A giant blob of abnormally hot rock beneath the Appalachian Mountains formed when Greenland separated from North America around 80 million years ago, new research suggests.
Scientists previously thought that this hot zone, known as the Northern Appalachian Anomaly, was left over after North America broke away from Africa 180 million years ago, but this theory does not stand up to new scrutiny, according to the study, published Wednesday (July 30) in the journal Geology.
“This thermal upwelling has long been a puzzling feature of North American geology,” lead author Thomas Gernon, a professor of Earth science at the University of Southampton in the U.K., said in a statement. “It lies beneath part of the continent that’s been tectonically quiet for 180 million years, so the idea that it was just a leftover from when the landmass broke apart never quite stacked up.”
Instead, the new findings indicate that the hot blob, which sits 125 miles (200 kilometers) deep and stretches 220 miles (350 km) across New England, appeared around 80 million years ago, when what are now Greenland and Canada were breaking apart. The results suggest that such blobs occasionally form in continent breakups, with possible knock-on effects for mountains, volcanoes and ice sheets.
Gernon and colleagues described how hot blobs form in a study published last year in the journal Nature. Hot blobs are created when material from Earth’s mantle rises to fill gaps in the crust left by rifting. This material eventually cools and becomes so dense that it sinks, or “drips,” setting off chain reactions in the mantle that the researchers called “mantle waves.”
There may be special conditions required for mantle waves to form, Gernon told Live Science in an email, including a steep temperature gradient where the dripping material enters the mantle. This means that not all continent breakups create mantle waves, Gernon said.
Related: North America is ‘dripping’ down into Earth’s mantle, scientists discover
For the new study, the researchers used direct geological observations and computer simulations to model plate tectonics and geodynamics. They simulated the initiation of a hot blob 1,120 miles (1,800 km) northeast of the Appalachians and found that geologic processes pushed the blob southwest at a rate of 12 miles (20 km) every million years. These results were consistent with previous estimates,…
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