The water is much deeper than previously thought. We know this thanks to… Diamonds

Tingting Gu from the Gemological Institute of New York, Purdue University and her team were discovered in African diamonds Inclusions, i.e. small fragments of other metals. Although these imperfections are undesirable in jewelry, they are intended for scholars It can be a very valuable guide about the environment deep under our feet. It was no different this time. Diamond imperfections contain water. This means that the environment in the Earth’s mantle is much wetter than previously thought.

Inclusions are found in a variety of diamonds called IaB. This is a rare type of diamond from the Karowe mine in Botswana which forms deep in the earth It is often there for a long time. Contains trace minerals, including: ringwoodite (magnesium silicate), ferropericase (magnesium / iron oxide), enstatite (a mineral from the silicate group, classified as a pyroxene – widely distributed). Ringwoodite – a form of olivine – is a hydrated mineral, which means that it has a structure compact water molecules (from 2.5% to 3% by weight). This means that It was in a humid environment at the time of its formation.

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while the pressure decreases, Ringwoodite disintegrates. Ferropericase and brdgmanite are formed, which in turn are transformed into enstatite. This is very important information because it tells us about the journey these minerals made from the center of the Earth. The deepest well drilled so far is only 11 km. Below, we are able to study the Earth using geophysical methods (including the speed and directions of propagation of seismic waves). Such a physical discovery, which “found itself” among researchers, is of very great value.

Thanks to the diamond coating that protects the minerals, they manage to preserve their properties. On their basis, the researchers estimated the temperature of formation of the mineral and the pressure under which it is located. After the analyzes, the depth of occurrence was estimated at 660 km, i.e. Repetitive cutout area The boundary between the upper mantle and the lower mantle.

Usually, when analyzing the water cycle, we focus on the Earth’s surface. Water evaporates, condenses, clouds are formed that bring rain. This then extends off the ground or absorbed into the soil (infiltrate). There, the water moves by gravity or creeps deeper, where it can reach, for example, a cave, where it will be temporarily excluded from the circulation.

But we also have some special places on Earth that give us little trouble on a daily basis. this is Subduction zones, that is, the places where plates meet and the heavier ocean plate enters the continental plate. And it’s problematic because earthquakes often happen here. This area is not completely closed off. Certain amounts of water can penetrate deep into our planet here. As a result of volcanic activity, this water is partially released in the form of steam. But it can go deeper.

Although an answer is frequently obtained, an object destructive search is necessary, in this case it was avoided. Scientists used a method of testing non-destructive substances called Raman spectroscopy. A laser is used to detect selected physical properties of a material. also used with X-ray diffractionThis allowed us to see the structure of the diamond without having to cut it. Interestingly, since 2008, scientists have found samples of this diamond only in meteorite samples.

source: Joe, T., Bamato, M.J., Novella, D.; et al. Aquamarine water fragments from the Earth’s mantle 660 km cutout sampled by diamond. nat. Geosci. (2022). https://doi.org/10.1038/s41561-022-01024-y

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