Deep in the Earth’s mantle, there two giant blobs. One sits under Africa, and the other is almost opposite to the first, under the Pacific Ocean. But these two points are not equally congruent.
New research finds that the point under Africa extends much closer to the surface – and more unstable – than the point under the Pacific Ocean. This difference could ultimately help explain why the crust beneath Africa has risen higher and why the continent has experienced many massive supervolcanic eruptions over hundreds of millions of years.
“This instability could have a lot of repercussions on surface tectonic movement, as well earthquakes Qian Yuan, a graduate fellow in geology at Arizona State University (ASU) who led the research, said:
pair of dots
Mantle points are more properly known as “Large Low Wave Velocity Interrupts” or LLSVPs. This means that when seismic waves generated by earthquakes travel through these deep regions, the waves slow down. This slowing indicates that there is something different about the mantle in this spot, such as density or temperature – Or both.
Scientists are not sure why the mantle points exist. Yuan told Live Science that there are two common hypotheses. One of them is that it consists of accumulations of crust from which it has slipped a landFrom the surface to the depths of the mantle. Another is that they are the remnants of an ocean of magma that may have existed in the lower mantle during Earth’s early history. In this way The ocean magma has cooled and crystallizedit may have left behind areas that were much denser than the rest of the mantle.
Yuan said previous studies have hinted that these two points may not be created equal, but none of this research has used global data sets that can easily compare the two. He and his advisor, associate professor of geodynamics at Arizona State University, Minming Li, examined 17 global seismic wave datasets to determine the height of each point.
They found that the African Point extends about 620 miles (1,000 kilometers) higher than the Pacific Point. That’s a difference of about 113 Mount Everest. In total, the mass of the Pacific Ocean extends 435 to 500 miles (700 to 800 km) up from the boundary between the core and the mantle. The African Point extends upwards from 990 to 1,100 miles (1,600 to 1,800 km).
The researchers then used computer modeling to find out which features of the points could explain these differences. They found that the most important ones are the density of the points themselves and the viscosity of the surrounding mantle. Viscosity refers to the ease with which mantle rocks can be deformed.
According to Yuan, for the African point to be much longer than the Pacific point, it would have to be much less dense. “Because it is less dense and unstable,” he said.
The African mass is still far from Earth’s crust – the total mantle is 1,800 miles (2,900 km) thick – but the instability of this deep structure could have implications for the planet’s surface. LLSVPs may be a source of hot plumes of rising mantle material. These plumes, in turn, could cause giant eruptions, tectonic disturbance, and possibly even continental breakup, Yuan said.
The African point “is very close to the surface, so there is a possibility that a large mantle plume will rise from the African point and may lead to more surface elevation, earthquakes and giant volcanic eruptions,” Yuan said.
These processes occur over millions of years and have been ongoing in Africa. Yuan said there appears to be a connection between the African Point and major volcanic eruptions. paper 2010 Published in the journal Nature He found that in the past 320 million years, 80% of the kimberlite, or massive eruptions of mantle rock that bring Diamond On the surface, it occurred just above the boundary of the African Point.
Yuan Li published their findings on March 10 in the journal natural earth sciences. They are now working on the origins of the dots. Although these results have not yet been published in a peer-reviewed journal, the researchers presented the findings at the 52nd Lunar and Planetary Science Conference in March 2021; This research suggested that the points It could be the remains of an object the size of a planet who – which It hit the Earth about 4.5 billion years agoMoon formation.
Originally published on Live Science.
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