Curtin WA School of Mines has conducted research on the world’s oldest mantle rocks and found the subduction of tectonic plates took place as long ago as 3.7 billion years earlier than commonly thought.
Subduction, the process where one tectonic plate sinks below another at converging plate boundaries, plays a major role in Earth’s geological, geochemical and geophysical evolution and is the major cause of much of the modern Earth’s volcanic and earthquake activity.
Professor Steven Reddy, Institute for Geoscience Research, said the timing of initiation of subduction in Earth’s evolution was controversial, and the discovery provided another strand of data that pointed to subduction being active early in Earth’s history.
The research team, comprising researchers from Australia and Switzerland, analysed the orientations of olivine crystals preserved in 3.7 billion year rocks from Isua, Greenland.
“The measured alignment of the olivine crystals is extremely rare and has only been found in relatively water-rich mantle above subduction zones,” Professor Reddy said.
“The results are consistent with subduction during the Eoarchaean era and show that ancient mantle rocks preserve a valuable record of geological processes over billions of years.”
Since subduction is the major mechanism of recycling material from the Earth’s surface back into the deep mantle, the initiation of subduction in Earth history has important implications for the mixing of chemical reservoirs and the geochemical and geological evolution of the planet.
Professor Reddy said that while many researchers had studied the alignment of olivine crystals from much younger rocks, no one had analysed such ancient samples.
“This result is quite surprising and is making us rethink what we understand about ancient mantle processes,” Professor Reddy said.
The paper, titled Earth’s oldest mantle fabrics indicate Eoarchaean subduction was published in Nature Communications and is available via http://www.nature.com/ncomms/2016/160216/ncomms10665/full/ncomms10665.html
