Laser view on helium-holders
Australian researchers have used a laser to visualise helium atoms trapped within individual mineral grains.
The new technique could be used to find out more about our geological history, and help monitor natural hazards like earthquakes and volcanic eruptions.
Researchers at Curtin University teamed up with Canberra-based high-technology instrument manufacturer ASI Pty Ltd to create a new laser microanalysis instrument, the RESOchron, which can measure helium at a resolution equal to one-tenth the width of a human hair.
Helium is generated in uranium and thorium-bearing mineral crystals.
It is a highly sought-after commodity for its use in medical and industrial applications, and is also 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,” said lead researcher Dr Martin Danišík.
Dr Danišík said that by using the RESOchron to repeatedly run a laser over a zircon crystal’s surface, the team was able to create the first helium 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.”
Professor McInnes, who first conceived the high-tech laser, said the ability to measure helium distribution 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.”