Written by Laura Glitsos Wednesday, 17 March 2010 08:54
WESTERN Australia’s Pilbara region is home to some of the oldest rock formations on Earth and now further evidence from these rock samples reveal new information on the very earliest crustal evolution.
UWA’s School of Earth and Environment Honorary Research Fellow Dr Martin Van Kranendonk was part of an international team that published the findings in an online study in Nature Geoscience.
“The Pilbara is one of the best natural laboratories in the world,” Dr Van Kranendonk says.
“People come from everywhere to study it, to travel through it, and appreciate it on all kinds of levels.”
After analysing volcanic, sedimentary and hydrothermal rocks, the team found contamination in the samples by a much older crustal element known as zircon crystals.
The findings confirm the Earth’s crust began forming between 4.3 and 4.5 billion years ago.
Dr Van Kranendonk says the Pilbara samples are the best-preserved and “freshest” samples they have ever been able to get.
“With the research that we just published we got some clues as to the time when there were no rocks recorded.”
He also says the earth formed from the solar nebula about 4.567 billion years ago but the oldest rocks found so far are 4.03 billion years old.
“So there’s a 500 million year window where there are know actual physical rocks preserved.”
This is because in the early history of the Earth the surface of the planet was still incredibly hot, so even though the ‘skin’ on the surface would form, it would get recycled back into the mantle.
“But we’re left with geochemical fingerprints of its existence and we have a few traces in WA of that period, in the form of tiny little crystals preserved in sandstone,” Dr Van Kranendonk says.
“We’ve dated those grains and they go back to 4.4 billion years old so there are tiny little relics of those early rock forming events.”
Dr Van Kranendonk says the oldest preserved rocks on Earth are found in North-Western Canada.
“The small area actually looks like it’s been melted, like someone has taken a big wooden spoon through rock taffy and swirled it all around, they are ‘messed up’.”
However, according to Dr Van Kranendonk , the Pilbara rocks are perfectly preserved and “look like they were placed down yesterday”.
In terms of industry impact, this geological study means a great deal to the mining sector.
“[The samples] help us understand how a piece of crust came to be where it is and why,” he says.
“So if I can tell someone that ‘this piece of crust is likely to have a lot of ore deposits because its had this happen to it’, then that company is going to be more interested in going somewhere.
“Things like when fluid moved through the crust, when it moved through and how many times, all have bearing on where to find ore deposits.
“Some of those factors are good for some types of ore deposits and some are good for others.”
Dr Van Van Kranendonk was part of an international team led by Macquarie University’s Dr Svetlana Tessalina as well as scientists from the Institut de Physique du Globe de Paris and the Geological Survey of Western Australia and Switzerland.
