While it is established that the genesis of diamonds necessitates subterranean carbon, and their characteristic pink hue arises from immense pressures exerted by converging tectonic plates, researchers at Curtin University have pinpointed a third crucial element for the emergence of pink diamonds at the Earth’s surface. This element is the extensional deformation of continental landmasses, a process of ‘stretching’ that occurred approximately 1.3 billion years ago during continental rifting.
Plate tectonic reconstructions showing the position of Argyle within the McArthur-Yanliao Gulf. Image credit: Olierook et al., doi: 10.1038/s41467-023-40904-8.
“A substantial proportion of economically viable primary diamond reserves are housed within kimberlite diatremes situated on Archean cratons. It is conventionally understood that ancient and robust continental lithosphere is indispensable for prolonged diamond formation,” stated Curtin University investigator Hugo Olierook and his associates.
“Nevertheless, the Argyle mine, located in Western Australia’s Kimberley region and representing the most significant source of natural diamonds discovered thus far, is an anomaly. It is one of the select few economically significant deposits found within a Paleoproterozoic orogen, adjacent to cratonic areas underlain by Archean bedrock.”
“Furthermore, Argyle is hosted in olivine lamproite, as opposed to kimberlite, and has been the source of over 90% of all identified pink diamonds,” they elucidated.
“The unearthing of Argyle in 1979 heralded a transformative shift, stimulating diamond exploration efforts in terrains other than Archean ones.”
“Despite its profound importance, the precise geodynamic forces responsible for the emplacement of such a distinctive diamond-bearing complex remain elusive.”
Through the application of laser microanalysis, employing beams finer than a human hair on Argyle samples, Dr. Olierook and his co-authors determined Argyle’s age to be 1.3 billion years, an estimation that predates previous assessments by a century.
“Argyle is situated at the juncture where the Kimberley region and the remainder of northern Australia converged millennia ago. Such a collision generates a weakened zone, or ‘scar,’ in the geological landscape that never fully mends,” Dr. Olierook explained.
“While the continental mass that would evolve into Australia did not undergo a complete fragmentation, the locale of Argyle experienced significant stretching, particularly along this pre-existing scar. This extensional episode created fissures in the Earth’s crust, allowing magma to ascend rapidly to the surface, carrying with it the pink diamonds.”
“Provided these three essential components are present — primordial carbon, continental collision, and subsequent crustal stretching — we posit that the discovery of a deposit akin to ‘the next Argyle,’ once the globe’s preeminent source of natural diamonds, is a distinct possibility.”
“Even with a comprehensive understanding of these requisite factors, the identification of another substantial concentration of pink diamonds will undoubtedly present considerable challenges,” he cautioned.
“The majority of known diamond deposits are concentrated in the interiors of ancient continents, as their associated volcanic features tend to manifest at the surface, facilitating their discovery by explorers.”
“Argyle, however, lies at the convergent boundary of two such primordial continents. These continental edges are frequently concealed beneath layers of sand and soil, leaving open the prospect that analogous pink diamond-bearing volcanic structures may still lie undiscovered, potentially within Australia itself.”
“The Argyle volcano has been responsible for yielding in excess of 90% of the planet’s pink diamonds, establishing it as an unparalleled provenance for these exceptionally rare and highly prized gemstones,” remarked Murray Rayner, a geologist with the international mining conglomerate Rio Tinto.
“By establishing the Argyle volcano’s age at 1.3 billion years and precisely locating it within a zone of early continental fragmentation on Earth, we have gained invaluable new insights into the geological processes governing diamond formation of this nature.”
The outcomes of this research have been disseminated in the esteemed journal Nature Communications.
_____
H.K.H. Olierook et al. 2023. Emplacement of the Argyle diamond deposit into an ancient rift zone triggered by supercontinent breakup. Nat Commun 14, 5274; doi: 10.1038/s41467-023-40904-8
