Deep in the Earth’s mantle, there Two giant bubbles. One is under Africa and the other is almost opposite 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 is more unstable – than the point under the Pacific Ocean. This difference may help explain why the crust under Africa has risen to a higher level and why the continent has experienced many massive volcanic eruptions over hundreds of millions of years.
This instability can have many repercussions on surface tectonic motion, as well earthquakes Qian Yuan, a geology graduate student at Arizona State University (ASU), who led the research, said:
pair of stitches
Mantle points are better known as 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 in the mantle at this point, such as density or temperature – Or both.
Scientists aren’t sure why the mantle patches 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. from here Ocean magma cooled and crystallizedIt may have left behind areas that were much denser than the rest of the mantle.
Yuan said previous studies have indicated that these two points may not be the same, but none of these studies used global data sets that could easily compare the two. He and his advisor, Arizona State University associate professor of geodynamics Mingming Li, examined 17 global seismic wave datasets to determine the height of each point.
They found that the African point extends about 1,000 kilometers above the Pacific point. This is 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 Point extends upwards from 990 to 1,100 miles (1,600 to 1,800 km).
point of instability
Then the researchers used computer modeling to find out which features of the points could explain these differences. They found that the most important were 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 the Earth’s crust – the total thickness of the mantle is 2,900 km – but the instability of this deep structure could have implications for the planet’s surface. LLSVPs can be a source of hot plumes of rising mantle material. These plumes, in turn, could cause giant eruptions, tectonic disturbances, and possibly even continental disturbances, 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 could lead to more surface uplift, earthquakes and giant volcanic eruptions,” Yuan said.
These processes take place over millions of years and are ongoing in Africa. Yuan said there appears to be a link between the African Point and major volcanic eruptions. paper 2010 Published in Nature He found that in the last 320 million years, 80% of the kimberlite, or massive eruptions of mantle rock that bring Diamond On the surface, it happened just above the Ponta Africana border.
Yuan Li published his findings on March 10 in the journal natural earth sciences. They are now working on point origins. While these results have yet to be 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 a planet-sized object from what It hit Earth about 4.5 billion years agoMoon formation.
Originally published on Live Science.
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