Deep in the earth’s mantle there is two giant bubbles. One is under Africa and the other almost opposite the first, under the Pacific Ocean. But these two points are not equally congruent.
New research reveals that the point under Africa extends much closer to the surface – and is more unstable – than the point under the Pacific Ocean. This difference may help explain why the crust beneath Africa has risen higher and why the continent has experienced numerous massive supervolcanic eruptions over hundreds of millions of years.
“This instability can have many implications for surface tectonic movement, as well as for earthquake Qian Yuan, a graduate researcher in geology at Arizona State University (ASU), who led the research, said:
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The mantle points are more properly known as “large low wave velocity interruptions” or LLSVPs. This means that when seismic waves generated by earthquakes pass through these deep regions, the waves slow down. This slowing indicates that there is something different in the mantle at this point, such as density or Temperature – Or both.
Scientists don’t know why mantle spots exist. Yuan told Live Science there are two common assumptions. The first is that it consists of accumulations of crust from which it slipped a terrainFrom 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 early in Earth’s history. This way Cooled and crystallized oceanic magmait may have left behind much denser areas than the rest of the mantle.
Yuan said previous studies had suggested these two points might not be the same, but neither of these studies used global data sets that can easily compare the two. He and his adviser, an associate professor of geodynamics at Arizona State University Mingming Li, examined 17 global seismic wave datasets to determine the height of each point.
They found that the African tip extends about 1,000 kilometers above the Pacific tip. That’s a difference of about 113 Mount Everest. In total, the mass of the Pacific Ocean extends from 700 to 800 km to the boundary between the core and the mantle. The African tip extends upwards from 990 to 1,100 miles (1,600 to 1,800 km).
The researchers then used computer modeling to find out what features of the dots might account for these differences. They found that the most important are the density of the dots themselves and the viscosity of the surrounding mantle. Viscosity refers to how easily mantle rocks can be deformed.
According to Yuan, for the African tip to be much longer than the Pacific tip, it would have to be much less dense. “Because it’s less dense and unstable,” he said.
The African mass is still far from the Earth’s crust – the total mantle is 2,900 km thick – but the instability of this deep structure could have implications for the surface of the planet. LLSVPs can be a source of hot plumes of rising mantle material. These plumes, in turn, can cause giant eruptions, tectonic disruptions and possibly even continental disruption, Yuan said.
The African tip “is very close to the surface, so it is possible that a large mantle plume will rise from the African tip and could lead to more surface uplift, earthquakes and giant volcanic eruptions,” he said. said Yuan.
These processes take place over millions of years and continue in Africa. Yuan said there appears to be a link between the African tip and major volcanic eruptions. paper 2010 Published in the journal Nature He found that over the past 320 million years, 80% of the kimberlite, or massive eruptions of mantle rock that bring diamond On the surface, it occurred just over the Ponta Africana border.
Yuan Li published his findings on March 10 in the journal natural earth sciences. They are now working on the origins of the points. Although these results have not yet been published in a peer-reviewed journal, the researchers presented the results at the 52nd Conference on Lunar and Planetary Sciences in March 2021; This research suggested that the points It could be the remains of a planet-sized object who, what It hit the Earth about 4.5 billion years agoFormation of the Moon.
Originally posted on Live Science.