Pink diamonds from the Continental Breakup were propelled to the surface of the Earth.

In modern society, diamonds are not typically connected to the end of romantic relationships. However, this is not true for the Argyle diamond mine in Western Australia, which used to be the largest supplier of pink diamonds in the world. Scientists have determined that the Argyle deposit was created during the break-up of one of the Earth’s oldest supercontinents, approximately 1.3 billion years ago. The research, published in Nature Communications, reveals how the splitting of continents could have led to the rapid emergence of diamonds and could provide clues for locating similar deposits in other areas.

Champagne and Diamonds

For centuries, diamonds have played a prominent role in the tales of the Miriwoong and Gija tribes in Western Australia. However, it wasn’t until 1979 that geologists from the Western world discovered diamonds in the region as well. The first diamonds were shipped from the Argyle mine in 1983, causing a significant increase in the global production of diamonds. Over the course of 37 years, the mine produced 865 million carats before closing in November 2020 due to economic reasons.

The deposit at Argyle has always been unique. While most diamond deposits around the world are found in kimberlite rich in carbon dioxide, Argyle is located in water-rich lamproite that comes from the Earth’s mantle. Unlike most diamond deposits that are found deep within ancient continental blocks, Argyle is situated on the edge of a rift zone. Additionally, the pink and brown diamonds at Argyle are distinct from the typically colorless diamonds found elsewhere.

A gemstone of pink hue may be desired by Barbie, but a specialist in gems would deem it flawed. According to Hugo Olierook, a geochemist at Curtin University in Australia and primary author of the latest research, pink diamonds are exclusively created through deformation.

Significant force is necessary to manipulate the atomic structure of diamond crystals and cause a shift in color. A small twist results in a pink diamond, while a larger twist produces a brown sugar hue.

According to Olierook and his team, it is believed that the diamonds found in Argyle underwent a change in color due to the collision of continental blocks, resulting in the formation of Nuna, an ancient supercontinent that existed before Pangaea. This event occurred approximately 1.9 billion years ago. When Nuna eventually split apart 1.3 billion years ago, the weakened rifts caused volcanic activity which brought diamonds up from their underground origins, similar to bubbles rising in a bottle of champagne, as explained by Olierook.

Previous research estimated that the diamond deposit in Argyle formed around 1.2 billion years ago, during a relatively inactive period in the area. However, Olierook and his team analyzed minerals from the rock containing the diamonds and determined that they are actually 1.3 billion years old. This aligns with the breakup of the supercontinent Nuna. The presence of deep volcanic activity at the rift zone during the separation of Nuna can explain the formation of Argyle’s diamonds.

Olierook stated that although correlation does not always imply causation, it appeared to be a sophisticated explanation in this case.

According to Olierook, there is evidence supporting the theory. A recent study on kimberlites also identified continental breakups as the cause of diamond deposits being propelled to the surface. Olierook expressed satisfaction in the fact that both scientific investigations, conducted by separate teams, arrived at the same conclusion.

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Olierook explained that the volcanic cone responsible for bringing Argyle’s diamonds to the surface also created a jumble of minerals. Some of these minerals were a result of the eruption, occurring after the diamonds were formed, while others had already existed prior to the eruption.

In order to determine the timing of crystal formation, scientists utilized a laser with a width of 30 micrometers to extract small samples from individual mineral grains found in the lamproite. They specifically focused on titanite, a mineral that was created soon after the volcanic eruption, and analyzed the levels of radioactive uranium and its stable byproduct, lead. This revealed the earliest potential date for the diamond eruption, which was approximately 1.26 million years ago.

The scientists used a laser to determine the maximum age by studying crystals of zircon and apatite found in the lamproite prior to the volcanic eruption. This revealed that the diamonds were brought to the surface approximately 1.3 billion years ago, matching the timeline of Nuna’s breakup.

The scientists conducted meticulous dating research, according to geochemist Maya Kopylova from the University of British Columbia, who was not part of the study. This approach is commendable, as some studies have only looked at overall rock samples, which provides an average age for all minerals present instead of individual grain ages.

According to Steve Shirey, a geochemist at Carnegie Science who was not part of the research team, the theory proposed by the researchers about the movement of supercontinents leading to the emergence of Argyle diamonds on Earth’s surface is most likely accurate.

The research provided scientists with a better understanding of the formation of a large diamond deposit, which could help them identify potential locations for similar discoveries. However, even if the theories presented in the paper are accurate, it is unlikely that there will be another surge in pink diamond findings. This is because rift zones, which are where the deposit was found, are not typically accessible and are often buried under layers of sediment. The Argyle mine is a unique case, as it happened to be located in a geologically favorable area at the right time for profitable mining. According to Kopylova, if pink diamonds are present in other rift zones, they are likely located at such depths that it is not feasible to mine them or even begin searching for them.

—J. Besl (@J_Besl), Science Writer

Reference: Besl, J. (2023). Pink diamonds from continental breakup found on Earth’s surface. Eos, 104. https://doi.org/10.1029/2023EO230401. Published on October 23, 2023.

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