They were created by enormous pressure within the Earth, are extremely beautiful and have always been fascinated by their sparkle: diamonds. In addition to colorless specimens that sparkle in the light, diamonds also come in many other colors. In northwestern Australia, for example, there is the Argyle diamond mine, which mined about 90% of all pink diamonds until it closed in 2020. But how the gemstones got into the Earth’s crust has long remained a mystery. A new interpretation has now been provided by dating minerals from the mine. As a research team reported in the journal Nature Communications, the findings could help find previously unexploited diamond deposits.
For their research, Hugo Ollerock of Curtin University in Perth and his team examined minerals from the Argyle Diamond Mine. To do this, they collected about two kilograms of samples and cut them into cubes ranging in size from 2 to 3 centimetres. They separated small amounts of it with a laser and used a high-resolution mass spectrometer to analyze what the crystals were made of and in what proportions. They also used this composition to determine the age of the samples. They achieved this using uranium’s atomic variants, isotopes 235what 238U. Because over millions of years, these elements decay into thorium isotopes, and finally into lead isotopes 207Lead and 206Lead. Since it is known how long decay takes – between 704 and 4,500 million years, depending on the decay path and its components – the scientists were able to determine the amount of decay products in the crystals they found and used that to determine the age of the crystals. Samples.
It reaches the Earth’s crust through cracks in the continental plate
These dates revealed that the minerals are about 1.3 billion years old, or 100 million years older than previously assumed. Accordingly, sediments and diamonds are formed by flows of materials from the deep layers of the Earth in the Earth’s mantle. In order for diamonds to reach the Earth’s surface, volcanic processes had to open a path to the Earth’s crust.
Ollerok and his team explain how this was achieved using the process of plate tectonics. At that time, according to the researchers, the ancient Nuna continent was torn apart: the Australian plate, which was then in the Northern Hemisphere, separated from the landmass that later formed North China. Although the Argyle Diamond Mine was not located directly on the plate boundary, the rock layers in this area were still expanding and becoming more unstable. Flows of volcanic material penetrated the Earth’s surface. The diamonds, which actually formed about 500 million years ago when tectonic plates collided under intense pressure, were able to rise through these volcanic channels.
The results not only explain the source of pink diamonds, but they are also promising. The research team, led by Hugo Ollerock, hopes their findings will enable the discovery of previously undiscovered diamond deposits in Australia.
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