US, WASHINGTON (ORDO NEWS) — The Earth’s mantle begins at a depth of about 30 kilometers and, reaching about 2,900 kilometers, passes into the iron-nickel core of the planet. Not a single drilled well has yet reached the mantle.
However, stone meteorites from a very widespread group of chondrites – “building debris” left over from the formation of the solar system – are similar in composition. This is also confirmed by the analysis of lava raised from the depths by volcanic processes.
On the other hand, much less heavy isotopes of iron are found in chondrites than in some volcanic rocks; this discrepancy is still a mystery. In addition, the lower 200-km layer of the mantle at the boundary with the core exhibits anomalous seismic properties.
The team of Charles Lesher, a professor at Aarhus University in Denmark, was able to explain these oddities. An article by scientists is published in the journal Nature Geoscience.
In the laboratory, they modeled the transition conditions between the lower mantle and the outer core, including high pressure (up to 2 GPa) and a temperature gradient that is much higher in the core (up to 2100-2300 kelvin). It was found that iron isotopes are separated in such a system: heavier atoms show greater mobility, they migrate to the region of low temperature and pressure, and accumulate there.
For billions of years, this process could easily lead to the saturation of mantle matter with heavy iron.
In addition, geologists conducted computer simulations of the migration of heavy iron on a larger scale. Calculations showed that these isotopes can penetrate not only into the mantle, but also rise higher. Carried away by mantle plumes, they can reach the earth’s crust and eventually be thrown to the surface by volcanoes as part of a basaltic lava.
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