Brazilian Diamonds Reveal Traces of Ocean Crusts

Earth scientists are trying to determine our planet's history through a variety of means, but recently they took to doing so by studying diamonds, some of the most expensive and rare rocks in the world.

Though, for commercial applications, clear diamonds are priceless, researchers are looking for the exact opposite. They want to find stones that have small inclusions of various minerals.

In these minute traces of materials, researchers can find inscribed several millions of years of changes that affected both the crust and the mantle covering Earth's nucleus.

This was recently evidenced in a research that was conducted by investigators at the University of Bristol, in the United Kingdom, on a batch of Brazilian diamonds.

The scientists discovered that the inclusions in these stones contained traces of both oceanic crust and sedimentary rock, which means that the samples are very old.

Sediments are deposited when seas retreat, or are carried by rivers at the sites were they flow into seas or oceans. Accumulations of the stuff therefore form on dry land, or on the ocean floor.

But the fact that the minerals were found in diamonds seems to indicate that the piece of crust where they appear was then pulled back into the mantle, the layer of molten rock on which the crust floats.

This is only possible through the process of subduction, in which a tectonic plate moves underneath another one, in which it slams. This apparently took the analyzed samples down to a depth of around 300 kilometers.

Diamonds are known to form only under intense pressure and heat, which can be found in nature only in the mantle. These conditions force carbon atoms together in the unique structure that forms diamonds.

But, sometimes, small impurities can remain trapped inside the newly-formed structures, and this is precisely what investigators are analyzing.

Experts estimate that some of the diamonds which were recently analyzed were formed some 100 million years ago, after the material making them up was submerged to depths between 300 and 700 kilometers in the mantle.

Details of the work were published this week, in the latest issue of the esteemed scientific journal Contributions to Mineralogy and Petrology.

The paper is entitled “Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina, Brazil: subducted protoliths, carbonated melts and primary kimberlite magmatism.”