A massive mass of unusually hot rock beneath the Appalachian Mountains formed when Greenland separated from North America about 80 million years ago, new research suggests.
Scientists previously thought the hot zone remained after North America left Africa 180 million years ago, but a study published on Wednesday (July 30) found that the theory cannot withstand new scrutiny.
“This thermal upwelling has long been an inexplicable feature of North American geology,” Prime Minister Thomas Gernon, a professor of geoscience at the University of Southampton in the UK, said in a statement. “It’s under a part of a continent that has been structurally quiet for 180 million years, so the idea that it was leftovers from when land broke has been left over never stacked.”
You might like it
Instead, new findings show that hot blobs, located 125 miles (200 km) deep and extending 220 miles (350 km) in New England appeared about 80 million years ago. The results suggest that such masses sometimes form in continental divisions, and may be knock-on effects on mountains, volcanoes and ice sheets.
Gernon and colleagues explained how hot blobs are formed in a study published in the Nature Journal last year. Hot masses are created as material from the Earth’s mantle rises and fills up the gaps in the crust left by lifting. This material eventually cools, becomes very dense, sinks, or “drips”, causing a mantle chain reaction that researchers call “mantle waves.”
There may be special conditions needed to form mantle waves, Gernon told Live Science via email. This means that not every continent’s division produces mantle waves, Garnon said.
Related: North America is “dripping” into the Earth’s mantle, scientists discovered
In the new study, researchers used direct geological observations and computer simulations to model plate tectonics and geodynamics. They simulated the start of hot blobs 1,120 miles (1,800 km) northeast of the Appalachians, and found that geological processes pushed southwest blobs at a speed of 12 miles (20 km) every million years. The results were consistent with previous estimates, according to the statement.
The team’s simulations show that the hot blobs could have helped raise the Appalachians when they got there, answering years of questions about why the Appalachians remain so high despite significant erosion over the past 20 million years.
“Heat at the roots of the continent can weaken and remove some of the dense roots, making the continent lighter and buoyant, just as hot balloons rise after ballast is dropped,” Gernon explained in a statement. “This has further elevated the ancient mountains over the past million years.”
The hot masses elsewhere can explain why mountains still stand with geology similar to the Appalachians, Garnon said. According to the statement, these masses could also explain the rare volcanic eruptions that bring diamonds to the surface of the Earth.
Looking at the Greenland blob
The study focused primarily on the northern Appalachian anomalies, but researchers also looked at “twins.” The anomaly, according to the statement, was born at the same continental split event, but on the other side of the cleft. The team noted that thermal currents are generated beneath the Greenland ice sheet, affecting the way ice today moves and melts.
“Ancient heat anomalies continue to play a key role in shaping the dynamics of the continental ice sheet from below,” Garnson said. “The surface shows little indication of tectonics ongoing, but the results of deep, ancient lifting still occur.”
The northern Appalachian anomalies are still moving, and researchers estimate that they will continue their path to New York in 10 to 15 million years.
As the hot mass leaves the Appalachians, the crust of the earth settles once again, Garnon said. “In the absence of additional structural or mantle-driven ridges, erosion will continue to wear the mountains and gradually reduce the altitude,” he said.
Overall, the results reveal that continental divisions and other major geological events can continue to affect planets for thousands, or even millions of years, researchers said in a statement.
“The idea that continental lifting can cause drops and cells of hot rock circulating at depths that extend thousands of kilometers inland, rethinks what we know about the edges of the continent, both today and in the deep past of the Earth.”
Source link
