Curtin University researchers have for the first time been able to visualise where helium atoms are trapped within individual mineral grains, providing information that can help to determine the geological history of the Earth’s crust and assist in monitoring natural hazards like earthquakes and volcanic eruptions.
The researchers, led by Professor Brent McInnes of Curtin’s John de Laeter Centre, teamed up with Canberra-based high-technology instrument manufacturer ASI Pty Ltd to create a new laser microanalysis instrument, the RESOchron™, capable of measuring helium at high resolution – to one-tenth the width of a human hair.
Dr Martin Danišík, lead author of a paper on the research published in Science Advances, said helium − generated over long periods of time in uranium and thorium-bearing mineral crystals − was a highly sought-after commodity used in medical and industrial applications. It has also been used by geoscientists to date rocks.
“Scientists have been using the helium dating technique to determine the age of minerals for over 100 years, but until now, nobody has been able to observe the actual distribution of helium within the crystal structure,” Dr Danišík said.
Dr Danišík said that by using the RESOchron to repeatedly raster a laser across a zircon crystal’s surface, the team was able to create the first helium abundance map.
“We then used numerical simulations to determine how thermal events in the Earth’s crust influenced helium abundance patterns in the crystal over geological time,” Dr Danišík said.
“By matching measured and simulated helium distributions, we were able to decipher the mineral’s geological history.”
[youtube]http://www.youtube.com/watch?v=O1kMei_JLCE[/youtube]
Professor McInnes, who conceived the instrument concept and assembled the project team, said the ability to measure radiogenic helium distributions in individual grains could help scientists understand more about the timing of fault movement, volcanic eruptions and mountain building processes, as well as assist in the exploration for mineral and petroleum deposits.
“We were surprised to discover extremely high concentrations of helium in cavities within crystals, and speculate that this could be useful in earthquake monitoring, because the crushing of minerals during fault motion should break open these cavities and release a flux of helium gas that can be detected at surface,” Professor McInnes said.
“Our team has previously demonstrated that minerals in diamond-bearing kimberlite pipes have uniquely low abundances of helium, and this technology can be used to rapidly scan exploration samples to both detect kimberlitic zircon and identify the age of the kimberlite pipe.”
Dr Bruce Godfrey, CEO of ASI Pty Ltd, said the company was pleased to collaborate with Curtin in the development of this innovative geochemical technique.
“We look forward to developing the instrument platform for the international market,” Dr Godfrey said.
A paper detailing the findings, Seeing is believing: Visualization of He distribution in zircon and implications for thermal history reconstruction on single crystals, was published recently in Science Advances.
