The subsoil is not a uniform pile of layers. Deep in the thick middle layer are two enormous thermochemical points.
To this day, scientists still don’t know where each of these massive structures came from or why these heights differ, but a new set of geodynamic models have landed on a possible answer to this latter mystery.
These hidden reservoirs are located on opposite sides of the world, and judging by the deep propagation of seismic waves, the point under the African continent is more than twice as high as that under the Pacific Ocean.
After running hundreds of simulations, the authors of the new study believe that the point under the African continent is less dense and less stable than its counterpart in the Pacific Ocean, which is why it is so much higher.
“Our calculations found that the initial size of the blobs does not affect their height,” explain Geologist Qian Yuan from Arizona State University.
“The height of the points is mostly controlled by their density and the viscosity of the surrounding mantle.”
3D view of the point in the Earth’s mantle below Africa. (Mingming Li/Arizona State University)
One of the main layers inside Earth is the hot, slightly sticky mess known as the mantle, a layer of silicate rock that lies between our planet’s core and crust. While the mantle is mostly solid, it behaves Tar on longer time scales.
Over time, plumes of hot magma rock gradually rise through the mantle and are thought to contribute to volcanic activity at the planet’s surface.
So understanding what happens in the mantle is an important endeavor in geology.
The African and Pacific Ocean points were first discovered in the 1980s. Scientifically speaking, these “super-pillars” are known as Large counties with low shear speed (LLSVPs).
Compared to the Pacific LLSVP, the current study found that the African LLSVP extends about 1,000 kilometers (621 miles) higher, supporting earlier estimates.
This vast difference in elevation indicates that both points have different compositions. How this affects the surrounding mantle, however, is unclear.
Perhaps the less stable nature of the African mounds, for example, could explain why there is such intense volcanic activity in some regions of the continent. It can also affect the movement of the tectonic plates, which are floating on the mantle.
Other seismic models have found that the African LLSVP extends up to 1,500 km above the outer core, while the Pacific LLSVP reaches a maximum elevation of 800 km.
In lab experiments seeking to reproduce Earth’s interior, both Africa and the Pacific mounds seem to sway up and down through the mantle.
The authors of the current study say this supports their interpretation that African LLSVP is probably unstable, and the same could be true for Pacific LLSVP, although their models did not show this.
The different compositions of the Pacific and African LLSVPs can also be explained by their origins. Scientists still don’t know where these blobs came from, but there are two main theories.
One is that piles are made of merging tectonic plateswhich slides into the mantle, is greatly heated and gradually falls to the bottom, which contributes to the formation of the point.
Another theory is that the points Remnants of the old collision Between Earth and the protoplanet Theia, which gave us our moon.
The theories are not mutually exclusive either. For example, Thea may have contributed more to one point; This may be part of the reason why they look so different today.
“Our combination of seismic results analysis and geodynamic modeling provides new insights into the nature of Earth’s largest structures in the deep interior and their interaction with the surrounding mantle,” Says yuan.
“This work has far-reaching implications for scientists trying to understand the current state and evolution of the deep mantle structure, and the nature of convection in the mantle.”
The study was published in natural earth sciences.
