Mar. 5, 1998 Thinking of going to Australia but dreading the long flight over the Pacific Ocean? Ponder this: if you'd been around 1.6 billion years ago, you could have walked from British Columbia.
That's because mounting evidence suggests that the land mass we know as Australia may once have been joined to North America at the Yukon before drifting apart about one billion years ago.
It sounds far-fetched, considering the thousands of kilometres separating the two continents today, but on a geological time scale it's easily possible, says Derek Thorkelson, a professor of earth sciences at Simon Fraser University. He's just wrapping up a five-year study that offers convincing evidence of the Yukon/Australia connection.
Thorkelson focused on a series of unusual rock formations, known as 'breccias,' scattered over 3,500 sq km in the Wernecke Mountains of east-central Yukon. Because these formations - some of which are several kilometres long - are strikingly different in appearance from surrounding rocks, geologists have long puzzled over their origins.
Thorkelson's study -- which involved extensive geological mapping, geochemical analysis and mineral assessment in the area -- shows that the breccias (pronounced 'bretch-ee-as") were formed from a series of underground explosions caused by violent expansion of gas from liquid.
"This process is fairly well understood and is not that uncommon," says Thorkelson. "But in this case, the process of brecciation led to the precipitation of important ore minerals, such as copper, gold, cobalt and uranium."
As it turns out, the Yukon breccia rocks look identical to some underground breccia rocks in southern Australia at the site of the huge Olympic Dam copper and gold mine. Eager to make a more positive match, Thorkelson sent rock samples from the Yukon site to a University of Alberta lab for dating.
The Yukon rocks are about 1.59 billion-years-old - the same age as the Olympic Dam rocks.
"This Yukon/Australia connection was suggested about 10 years ago," says Thorkelson, "but there was no age determination of any quality. With this new information, we're able to confidently draw a direct correlation."
Not suprisingly, mineral exploration in the Wernecke Mountains has intensified in recent years.
Thorkelson notes there are other geological clues pointing to a Yukon/Australia link. It's even speculated that a third continent, Antarctica, was part of the puzzle.
Still skeptical? Don't forget, says Thorkelson, that the earth is estimated to be about 4.5 billion-years-old. Movement of the earth's crust - known as plate tectonics - likely began about three billion years ago. By contrast, the separation of the Americas from Europe and Africa to form the Atlantic Ocean happened a mere 200 million years ago.
"In 1.6 billion years, there could have been numerous openings and closings of ocean basins," he says. "North America and Australia could have been involved in several continental collisions and separations between then and now.
"So in a geological sense, it's not remarkable putting these continents together. The interesting thing is trying to find out where they were together."
Thorkelson will outline the results of his Yukon breccia study at the upcoming Lithoprobe conference, which takes place this week (March 5-8) at SFU's Harbour Centre campus.
Lithoprobe is a 20-year, $100 million national geoscience project to develop a comprehensive understanding of the evolution of the North American continent. As many as 600 earth science researchers across the country are working on studies related to 10 geological transects, or cross-sections, of Canada.
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