Diamonds formed from the ocean floor
Scientists have found confirmation of the theory that the initial substrate for formation of diamond are deposited on the bottom of the oceans, writes the Chronicle.info with reference to Hvilya
Laboratory experiments that mimic conditions at a depth of hundreds of kilometers, showed that the reaction substances from the bottom of the oceans to reproduce the observed diamonds from the composition of salts, the authors write in the journal Science Advances.
Diamond — one of the modifications of carbon, which is formed at high pressure. In the case of Lands suitable conditions are formed in the upper layers of the mantle at a depth of a few hundred kilometers. Crystallization of stones to occur in the base of the cratons (old and fixed parts of the continental lithosphere). Subsequently, they arrive on the planet’s surface through a specific type of volcanic activity, which leads to the formation of kimberlite pipes.
Gem-quality stones are usually composed of pure carbon, but there are also minerals with inclusions, which are fast-growing fibrous diamonds. The latter is usually not used for making jewelry because often they are not transparent and contain specific impurities. Typically, these diamonds are used in the manufacture of tools, they were crushed, and the resulting dust used, for example, for use on drill bits.
The exact conditions under which diamonds are formed, however, remain unknown. In particular, it cannot explain the high relative concentration of potassium compared to similar compounds of sodium, dissolved in the liquid inclusions in diamonds. The balance of the elements is not predicted for the mantle. In 2005, Nature published an article in which it has been suggested that liquid inclusions are remnants of ancient water from the oceans that were locked in sediment minerals and ended up on depth as a result of subduction of the crust. However, this hypothesis does not explain data for potassium.
In work led by Michael förster (Michael Förster) from Macquarie University in Australia, scientists tried to simulate the conditions in the mantle by heating and squeezing the sample which is recovered from the bottom of the ocean sediments, and peridotite is the typical mineral of the upper mantle. The experiments were carried out at a pressure of from 3 to 6 GPA and temperatures from 800 to 1100 degrees Celsius, which corresponds to the parameters of the environment in the mantle at depths of 100 to 200 kilometers.
Analysis of the obtained samples showed a high ratio of concentrations of potassium salts for sodium salts, similar to the observed in fibrous diamonds. Scientists also noticed the formation of a sodium-rich mineral pyroxene, which included a substantial proportion of the element, shifting the ratio in the inclusions is in favor of potassium.
The results allowed the authors to propose a modified theory of the origin of diamonds and their inclusions. According to her, the plot of ocean bottom must go down to a depth of not less than 200 kilometers. This dive should proceed fast enough, as high pressure should be applied to effect complete melting of the substance. During this process locked up in the clays and sediments in the water will also be at depth, where dissolution of the surrounding substances and reaction with peridotite will allow to form the desired mixture, which then kristallizuetsya diamonds with inclusions. However, there are data about the origin of some diamonds at considerably greater depths, as well as on the early Earth, such as stones of the new theory is not applicable.
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“We have shown that the processes leading to the growth of diamond due to the recycling of oceanic sediments in subduction zones, says förster. — In the experiments we also received a minerals that are essential ingredient for the formation of kimberlite magmas, which then transferred the diamonds to the surface of the Earth.”