It was previously believed that the Earth’s transition zone was a dry sponge, but a recent study revealed that there were reserves of water there. More information about this region between the coats can be found by looking at a Botswana diamond.
The transition zone (TZ) is the layer that separates the lower and upper mantle of the Earth. It lies between 255 and 410 miles below the surface.
Peridot and Ringwoodite
About 70% of the Earth’s upper mantle is made up of the mineral olivine, also known as peridot, which is olive green in color. Under extreme pressures of up to 23,000 bar in the TZ, olivine undergoes a change in crystal structure. It grades into denser wadsleyite at a depth of about 410 kilometers in the upper part of the transition zone and into even denser ringwoodite at a depth of 520 kilometers.
Professor Frank Brenker of the Goethe University-Institute for Geosciences Frankfurt said that the movement of rock in the mantle is significantly impeded by these mineral transformations.
As an illustration, mantle plumes, which are rising columns of hot rock emerging from the deep mantle, sometimes stop abruptly just below the transition zone. The mass moving in the opposite direction also stops moving. According to Brenker, subduction plates often struggle to penetrate the entire transition zone. This means that there is a large graveyard of subduction plates in this area below Europe.
Get stuck on the Earth
However, until now it was unclear what long-term effects the “sucking in” of particles into the transition zone would have on its geochemical composition and whether there would be more water present.
According to Brenker, subduction slabs also graft onto deep seabed sediments inside the Earth. Large amounts of carbon dioxide and water can be stored in these sediments, but it has been difficult to determine whether or not there is significant water storage in this region because it is not known exactly how much has entered. in the transition zone in a more stable form as hydrous minerals and carbonates.
There is no doubt that the current situation favors it. The transition zone could theoretically absorb six times more water than our oceans due to the ability of thick wadsleyite and ringwoodite minerals to hold large amounts of water, unlike peridot at shallower depths. Brenker says that although the boundary layer has an enormous capacity to hold water, it was unclear if it actually did.
Botswana diamond, ocean inside the earth
A recent international study that examined a Botswana diamond from Africa revealed the solution. It was created at a depth of 660 kilometers, just at the boundary between the lower mantle and the transition zone, where ringwoodite is the dominant mineral.
Even among incredibly rare diamonds of remarkably deep origin, which make up only 1% of all diamonds on earth, diamonds from this location are extremely rare. Due to the abundance of ringwoodite inclusions, studies have determined that the stone contains a high water content. The research team was also able to determine the chemical composition of the stone.
It was nearly identical to every piece of mantle rock found in basalts around the world. This demonstrated that the diamond unquestionably came from a typical component of the Earth’s mantle.
According to Brenker, their study, published in Nature, showed that the transition zone, TZ, is not a dry sponge but rather retains a significant amount of water. Additionally, it advances our understanding of Jules Verne’s theory that the Earth contains an ocean. The discrepancy is that instead of an ocean, Brenker claimed there was hydrated rock, which doesn’t feel wet or dripping.
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Hydrated rock minerals
In a diamond from the transition zone, hydrated ringwoodite was first discovered in 2014, according to Scientific American. In this investigation, Brenker also participated. However, due to the small size of the stone, it was impossible to determine its precise chemical composition.
As a result, it was unclear how representative the initial study was of the mantle as a whole, as the diamond’s water content could also have been the product of an unusual chemical environment. On the contrary, the inclusions in the 1.5 cm Botswana diamond that the research team examined in the present study were large enough for the precise chemical composition to be defined, which provided definitive evidence for the preliminary results of 2014.
The high water content of the transition zone has significant effects on the Earth’s dynamic environment. Hot mantle plumes rising from below that become trapped in the transition zone are an example of what this entails. There, the water-rich transition zone is heated, causing new, smaller mantle plumes to emerge, which then absorb water that has been stored in the transition zone.
The water in the mantle plumes is forced to release, which lowers the melting point of the emerging material if these narrower, water-rich mantle plumes migrate further up and cross the upper mantle boundary.
As a result, it melts right away rather than just until it hits the surface, as is usually the case. Mass movements are more dynamic due to the decrease in the overall tenacity of rock masses in this region of the Earth’s mantle. The transition zone, which usually serves as a barrier to zone dynamics, is unexpectedly becoming a major force in the movement of materials across the world, reports Sci-Tech Daily.
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