There are two giant blobs deep within the Earth's mantle. One is under the Pacific Ocean, and the other is opposite to it, sitting under Africa. The two blobs are reportedly not evenly matched.
Enormous Blob Deep Beneath Africa
Scientists initially discovered the two enormous structures through seismic measurements. These anomalies are located above the outer core in the lower mantle, between 400 and 1,600 miles beneath the planet's surface.
The Pacific Ocean is home to one blob, and the other is in Africa. They are referred to as Low-Shear-Velocity Provinces (LLSVPs), and it is known that they impact processes in both the core and the mantle. The extremely dense "thermochemical piles" that make up the blobs are assumed to be made of recycled oceanic crust or other iron-rich material.
The African blob has a maximum height of roughly 990 to 1,100 miles, whereas the Pacific anomaly is between 430 and 500 miles high, placing the African blob about 620 miles higher than the Pacific LLSVP.
According to Qian Yuan, a graduate associate in geology at Arizona State University (ASU), who led the study, the African blob must be significantly less dense for it to be so much taller than the Pacific blob. He added that since it's less dense, it's more unstable.
The blob under Africa stretches far closer to the surface than the blob under the Pacific. This distinction may eventually explain why Africa's crust has been raised upward and why the continent has experienced so many enormous supervolcano eruptions over hundreds of millions of years.
According to Yuan, this instability may significantly impact earthquakes, supervolcanic eruptions, and surface tectonics. Although the African blob is still far from the Earth's crust and the mantle is 1,800 miles (2,900 km) thick overall, the instability of this deep structure may affect the planet's surface.
Hot plumes of mantle material that rise upward may originate from LLSVPs. Yuan added that these plumes could trigger supervolcano eruptions, tectonic shifts, and possibly even continental fractures.
What's Large Low-Shear-Wave-Velocity Provinces(LLSVPs)
The mantle blobs are called "large low-shear-wave-velocity provinces," or LLSVPs. This implies that seismic waves from earthquakes slow down as they pass through these deep mantle zones, suggesting that the density, temperature, or both of the mantle's properties may differ at these locations.
The existence of the mantle blobs is unknown to scientists. According to Yuan, two popular theories exist. First, they are composed of crustal accumulations that have subducted from the Earth's surface to a substantial depth in the mantle. Another theory suggests that they are the remains of a magma ocean that may have once filled the lower mantle during the planet's early history. Regions that were denser than the rest of the mantle may have been left behind as this magma ocean cooled and crystallized.
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