Continents move across Earth's surface, forming so-called 'supercontinents' at specific moments. Hundreds of millions of years later, they break apart, sometimes traveling thousands of kilometers before converging again in a different form. This process is known as the 'supercontinent cycle'.
Tectonic plates move primarily because oceanic plates dive deep beneath Earth's surface to depths exceeding thousand kilometers. Examining these processes is complicated because the oceanic crust 'disappears' into Earth's mantle. Furthermore, studying the continental crust provides little insight into the deep workings of Earth. In this regard, ancient diamonds provide information about the deep plate tectonic engine of Earth and its connection to the supercontinent cycle.
The researchers, led by VU alumna Suzette Timmerman from the University of Bern, studied the evolution of the Gondwana supercontinent from the bottom up. They analyzed super-deep diamonds formed at depths of up to 700 kilometers beneath Earth's surface to understand how material was added to the base of the supercontinent. In doing so, they discovered a previously unknown geological process: the large-scale accumulation of material from subducted plates, so states the research published in Nature.
Supercontinent grows 'from below'
A team of diamond specialists in laboratories at the University of Alberta, Carnegie Institution for Science, Vrije Universiteit Amsterdam, University of Bristol, and University of Padua examined small (< 100 microns) silicate and sulfide minerals in the diamonds. They used advanced techniques, allowing them to chemically analyze tiny amounts of material (a few picograms, 10-12 grams).
The research indicates that the diamonds originated deep beneath Gondwana when the supercontinent covered the South Pole. The diamonds formed from an oceanic plate driven to great depth that overtime was heated and became buoyant. These rocks, along with the diamonds, were carried to the bottom of Gondwana, causing the supercontinent to grow as if 'from below'.
Through this discovery, we gain more understanding of how continents grow, Gareth Davies says, and it aids us in shaping a sustainable future. "By better understanding what happens deep within Earth, we can more effectively search for strategic metal deposits such as rare earth metals often formed in ancient parts of Earth. And these rare earth metals are necessary for producing the vital technology for the energy transition, wind turbines for example."
About 120 million years ago, Gondwana began to break apart, giving rise to oceans, such as the Atlantic Ocean. Approximately 90 million years ago, the diamonds reached Earth's surface through volcanic eruptions known as kimberlites. These volcanoes are currently located in Brazil and West Africa, two crucial components of the former Gondwana. Conclusion? Attached to their base, the diamonds embarked on a journey from the south pole after the rupture of the supercontinent.
The VU team, Janne Koornneef and Gareth Davies, will continue to study diamonds from across Southern Africa to obtain a better understanding of the scale and timing of the 'growth from below' further improving our understanding of large scale geological processes that shape the continents on which we live.