The new model was developed over the last couple of years and stemmed from a remarkable coincidence involving two separate groups of researchers.
The groups are led by Ross Cayley, senior geologist with the Geological Survey of Victoria, and
Professor Louis Moresi, a computational geoscientist now working at the University of Melbourne.
The story of their meeting of minds and the surprising insights that followed reads like a great script for a movie.
Cayley told MiningNewsPremium that teams of geologists and geophysicists at the GSV had been exhaustively mapping the rocks of Victoria for 20 years.
“Victoria is not a large state, but we realised we had a unique opportunity because it’s the only state with bedrock outcrop that spans the entire width of the eastern Delamerian fold belt and the younger Lachlan fold belt farther east.
“That doesn’t happen in any other state, so we knew the rocks in Victoria could hold the key to understanding the big picture from Tasmania right up to Queensland.”
Cayley, who has been mapping in the field with GSV since 1990, said the more he looked, the more confusing the picture became.
“We had some major realisations along the way. One of these was about 10 years ago, when we established that a Tasmanian microcontinent extended under Bass Strait and beneath central Victoria.
“We didn’t understand the full implications – we just knew it was there.”
The second breakthrough stemmed from deep seismic transects. The first of these was across central Victoria in 2006 as part of a Predictive Mineral Discovery-Cooperative Research Centre (PMD-CRC) collaboration with Geoscience Australia. The second transect was in western Victoria in 2009, funded by the federal government’s earth science infrastructure body, AuScope.
“The deep seismic gave us answers about the regional-scale geometries that our mapping had suggested and confirmed thinking that western Victoria was an ancient subduction zone.
“A third critical breakthrough came from processing and interpretation of aeromagnetic data acquired over the Murray Basin, by Dr Robert Musgrave from the Geological Survey of NSW.”
Cayley realised that, in conjunction with the field geology from Victoria, the interpreted NSW data could constrain a radical new tectonic model for the geology of the whole Lachlan Fold Belt.
“Putting that all together, we came up with a crazy model with swirling fold belts that wrapped around the Tasmanian microcontinent.
“It was so radical that it was hard to believe. We could not find examples anywhere else in the world and had no real idea how to demonstrate that the processes driving our model could have happened.”
What Cayley did not know was Moresi and his research group at Monash University was having exactly the same problem for an entirely different reason.
By coincidence, Moresi had been using a newly developed four-dimensional numerical modelling tool known as Underworld (also funded by AuScope) to explore what happened at crustal scale when a microcontinent was drawn into a subduction zone.
His entirely conceptual work had produced a radical picture of swirling fold belts without any known analogue, but it was exactly as Cayley and his team had mapped in the rocks of Eastern Australia.
The meeting of minds happened when a mutual colleague, Dr Peter Betts, noticed the remarkable match in results. He twigged that the cause of the Australian chaos was the likely collision of the Tasmanian microcontinent into the Lachlan Fold Belt subduction zone hundreds of millions of years ago.
“Its really good when you reach the same idea from completely directions. It gives you a sense that we really might be on to something,” Cayley said.
Out of this unexpected collaboration came a conceptual paper*, published in Nature in March 2014, makes eastern Australia the type locality for a radical new geodynamic and geological process with worldwide application.
As for the eastern Australian details, that is work still in progress between Cayley and Musgrave.
The new model has huge implications for mineral exploration in eastern Australia, according to Cayley.
“Most of this tectonic activity in the eastern states took place between 500 million and 400 million years ago, and that’s when most of the really big mineral deposits were formed.
“The model explains how mineralised systems can be completely dismembered and disrupted, and shows where they can be transported thousands of kilometres and buried under younger rocks.
“We have mapped enormous folds that suggest whole new regions across eastern Australia that might offer repetitions of provinces that elsewhere have proven rich in mineral discovery.”
These newly prospective areas include western Victoria, central New South Wales, southeastern Queensland and the northeast of central Victoria.
“For example, this will be a very powerful template for explaining most of southeastern Queensland’s geology.
“No one has really explored through the younger rocks that cover all that. The setting was not understood and it was frankly thought to be too hard to figure out. It still might be beyond us, but at least we now have a model that is a starting point. It provides answers that we can test.”
In Victoria, two mineral explorers – Stavely Minerals and Catalyst Metals – are already moving quickly to capitalise on the new leads generated by Cayley and the rest of the GSV team.
Stavely is searching for porphyry copper in western Victoria in a setting that is believed to have analogies with the great copper discoveries in Chile.
Catalyst is searching under the Murray Basin sediments for repetitions of the great Bendigo gold fields, and recently struck highly encouraging intersections after moving further east on the advice of the GSV team.
"The new model is actually going to deliver for Victoria, New South Wales, Queensland and Tasmania in quite a big way once the full impact of it is understood,” Cayley said.
* The paper: (Moresi, L, Betts, P G, Miller, M S and Cayley, R A, 2014. Dynamics of continental accretion. Nature. 508, pp. 245-248 doi:10.1038/nature13033)
