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Curtin researchers ‘muddy’ current thinking on Earth’s mantle

Media release

Curtin University researchers have for the first time discovered the melting of mud in the Earth’s mantle, providing insights into the nature and history of the continental crust.

The paper in GEOLOGY published by Geological Society of America has significant bearing on the understanding of how the Earth’s rock cycle operates.

After several research expeditions to Oman and the United Arab Emirates, researchers found that the geochemical signature in the mineral zircon conclusively shows that mud from the ocean floor subducts deep into the mantle, where it then melts to form granite.

Lead Curtin researcher Dr Christopher Spencer from the Department of Applied Geology in the Curtin WA School of Mines said the findings provide new insights into how materials are recycled at the boundaries between continents and oceans, also known as subduction zones.

“The results from our research provide new information into the nature and history of the continental crust and mineral resources found within it,” Dr Spencer said.

“This discovery is crucial as it is the first time we have directly observed sedimentary material that melted in the mantle, as previous research has only speculated on this process.

“Our research discovered the highest oxygen isotope signature ever reported for zircon. Finding the zircon and the granite within the mantle rocks was extremely unexpected.

“Identifying the presence and determining the extent of mud melting in the mantle has important implications for understanding the effects on the composition of the mantle over time.”

The study was carried out with researchers at the John de Laeter Centre at Curtin University, as well as the Universities of St Andrews, Derby, Oxford, and Edinburgh in the United Kingdom, the University of Stellenbosch in South Africa and The University of Western Australia.

Co-author Dr Aaron Cavosie also from the Curtin WA School of Mines said the research gives us fresh insight into how the zircon records large-scale tectonic plate processes.

“The mineral zircon records many geological processes, from the creation of the Earth’s earliest oceans, glacial process, metamorphism, and recycling of the Earth’s crust,” Dr Cavosie said.

“The zircon we analysed are off-the-charts in terms of oxygen isotope ratios which can only result from melting mud and finding these in the exposed the mantle is incredibly exciting.”

The research was carried out as part of the Early Career Curtin Research Fellowship awarded to Dr Christopher Spencer.

The full research paper, Evidence for melting mud in Earth’s mantle from extreme oxygen isotope signatures in zircon, can be found at: http://bit.ly/2xcMspu