Billion-year-old geology locates critical minerals

Eclogite from Norway. Image: Dr Derrick Hasterok, University of Adelaide.

Researchers from the University of Adelaide have discovered how a billion-year-old geological mystery could help locate the critical minerals of today.

Eclogites are known to have disappeared from geological records between 1.8 and 1.2 billion years ago, before reappearing.

Upon their resurgence, a concentration of trace elements found in igneous rocks has been recognised and these trace elements presented a link to critical minerals.

The paper, titled Mantle heating at ca. 2 Ga by continental insulation: Evidence from granites and eclogites was written by lead author Renee Tamblyn and her associates.

Tamblyn explained the importance of her team’s discovery.

“We found evidence from the trace element chemistry of granites that suggests a large-scale heating of the continents around two billion years ago that corresponds with the assembly of Nuna, a supercontinent which completed its formation 1.6 billion years ago,” Tamblyn said.

“The Earth has generally been cooling since its formation, but Nuna had an insulating effect on the mantle, rather like a thick blanket, which caused temperatures to rise beneath the continents and prevent the preservation of eclogites and change the chemistry of granites.

“The changes in chemistry resulting from this unusual warming event during Earth’s geologic past could help to locate certain critical minerals by looking for rocks formed before or after this heating event – depending on which element is of being looked for.”

Australia presents a suitable sample for the research to continue, as the continent has regions both older and younger than the 1.8-billion-year mark when the eclogites disappeared.

“The rocks in the Northern Territory and north west Queensland are a little older than the 1.8-billion-year mark so may be a place where we can continue our investigations into this mysterious geological case,” Hasterok said.

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