Below New Hampshire is a huge chunk of incredibly hot rocks. That may be part of why the Appalachian Mountains are still taller, according to new research. But it is moving slowly, moving on to New York courses within the next 15 million years.
Called the Northern Appalachian Anomaly, or NAA, this hot rock blob is about 124 miles (200 km) below the New England mountain range and is 217-249 miles (350 km and 400 km) wide. It is considered a thermal anomaly because it is located in the athenosphere, or the semi-molten layer of the Earth’s upper mantle, and is higher than its surroundings.
The rock formations in this part of the interior of the globe are unusual, and scientists previously thought that North America was formed when it left Northwest Africa 180 million years ago.
However, a new study published in Journal Geology on July 29 suggests that the anomalies are linked when Greenland and North America separated 80 million years ago.
At a speed of 12.4 miles (20 km) per million years, the thermal anomaly traveled about 1,118.5 miles (1,800 km) from its origin as the Earth’s crust burst near the Labrador Sea between Canada and Greenland.
Hot Rock Mass has long been an inexplicable feature of North American geology, according to Chief Research Author Tom Gernon, a professor of geoscience at the University of Southampton in the UK.
“It’s under a part of the 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,” Gernon said in a statement.
Instead, rock blobs help explain why ancient mountains like the Appalachians are not as eroded as expected over time.
“Heat at the roots of the continent can weaken and remove some of the dense roots, making the continent lighter and more buoyant, just like hot balloons rise after ballast is dropped,” Gernon said. “This has further raised the ancient mountains over the past millions of years.”
New insights into BLOBs could help scientists better understand other similar geological anomalies around the world. This includes those under Greenland in northern Greenland, which may be the siblings of the northern Appalachian anomaly, and the effects of these rare features on the surface of the Earth.
To explain the origin and current location of the rock blob, scientists used the “mantle wave” theory proposed in a previous study.
This idea is similar to the process of unfolding within a lava lamp. After a continental fissure or fall apart, the hot, dense rocks separate from the base of the tectonic plates of wave-generating masses beneath the Earth’s crust.
As the continent grows and splits, the space opens under the breakpoint and is rapidly filling up with semi-molten asthenospheres, Jane said. The raised material is rubbed against the newly broken, cold, broken edges, allowing the material to cool, cluster and sink. This is a process known as edge-driven convection. Hottest mantle material creates warmer areas known as thermal anomalies, said co-author Sasha Bruhn, a professor at the GFZ Helmholtz Geoscience Centre in Potsdam, Germany.
“This sudden movement disrupts the edges of the continent’s roots and causes a chain reaction,” Garnon said. “Like a falling domino, root masses begin to drip down one after another. This is a gravity-driven process known as Rayleigh Taylor’s instability. These “drips” move inland away from the lift.
Convective rock flow continues slowly, ripples over millions of years, leading to rare volcanic eruptions that either bring diamonds to the surface of the Earth or help raise mountains.
“The idea that continental lifting can cause drops and cells of hot rock circulating at depths that span thousands of kilometers inland, rethinks what we know about the edges of the continent, both today and in the deep past of the Earth.”
For that study, the team used seismic waves to image the interior of the Earth and used geodynamic simulations and tectonic plate reconstruction to track the origins of northern Appalachian anomalies.
“Tracing the wave path back from where we are now would have formed a cleft and be born under the margin of the cleft in the Labrador Sea, when we were close to the point of the continent’s split.”
Maureen D. Long, Professor Bruce D. Alexander ’65 and chairman of Yale’s Department of Earth and Planetary Sciences, her team has several active research projects studying anomalies in North Appalachia.
Although not involved in this study for a long time, her research group has collected new seismic data from an array of local seismometers to capture more detailed images of rock blobs. A new model shared in a recently published study has helped for a long time, and her colleagues have come up with all possible ways to interpret captured images, she said.
“It’s exciting to see a new creative model proposed for the origins of the northern Appalachian anomalies. “I don’t think our conceptual model of how the NAA, including this new, was formed, does a perfect job of explaining all observations, but it’s great to see a new idea that brings some new ideas to the table about this.”
Looking forward to it, the team shows that the modelling shows that the centre of the anomaly will pass under New York within the next 15 million years.
“It’s a really interesting puzzle for geologists to think about what anomalies will look like in the future,” Long said.
But what does this movement mean to the Appalachian Mountains? This range formed when it collided with other crustal plates during the Paleozoic era, between 541 and 251.9 million years ago, and experienced new growth, between 541 and 221.9 million years ago, 141 million years ago, when Pangaea broke around 180 million years ago.
According to new research, Rockblobs may have also contributed to uplifting the mountains during the Cenozoic era over the past 66 million years.
“This anomaly could have played some kind of role in shaping the geological structures above it,” Long said. “For example, some studies suggest that the lithosphere above the NAA (the top mantle that makes up the crust and tectonic plates) is particularly thin, and the anomaly may play a role in thinning the plate above it.”
As the Rockblob moves, the crust under the Appalachians will likely settle again and stabilize, Janeson said.
“In the absence of further structural or mantle-driven uplifts, erosion continued to wear the mountains and gradually reduced the elevation,” Gernon said.
Additionally, the team believes that the split between Greenland and North America may have produced another thermal anomaly that emerged from the other side of the Labrador Sea. This second anomaly adds to the heat flow at the base of the ice sheet on the thick continent, affecting ice movement and melting, the study authors said.
“The surface shows little indication of ongoing tectonics, but the results of deep, ancient lifting are still unfolding,” Gernon said in a statement. “The legacy of continental division in other parts of the Earth system may be much broader and longer lifespans than we previously realised.”
Jun Lin Hua, a seismologist and professor at the University of Science and Technology in China, said he believes the mechanisms of research explaining anomalies are novel and can be applied to other regions where lifting occurs. Hua was not involved in this study, but recently wrote a study that found that the underside of the North American continent drip a mass of rock.
“The mechanisms presented in this study show a large potential solution for the puzzle, but further confirmation of this may require more relevant observation and modeling work, and as mentioned in the paper, multiple mechanisms may play a role together,” Hua said. “In any case, personally, this is a great piece that opens new doors to deepening understanding of the region.”
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