Researchers at the University of Alberta have found evidence that a 2,000-kilometre corridor stretching diagonally across northern Canada was under tremendous pressure to split in two about 2.7 billion years ago. It is the first evidence suggesting enormous continental landforms and plate tectonics existed that long ago.
"Rifts are one hallmark of plate tectonics, and there is a huge debate in our field about whether or not large continents and plate tectonics existed on Earth in the Archean age, which is pre-2.5 billion years ago," said Dr. Larry Heaman, a professor of earth sciences at the U of A.
"Our findings suggest that a form of plate tectonics did occur in the Archean," said Dr. Russell Hartlaub, a post-doctoral fellow working with Heaman and lead author of a paper on the Archean rift discovery that appears recently in Precambrian Research.
For the past six years, the researchers have been studying rocks in the northern Lake Athabasca region of Saskatchewan. These rocks are collectively known as the Murmac Bay Group, and they are part of a corridor that runs from northeast Alberta to Baffin Island. Recently, Hartlaub and his colleagues discovered a sequence of Archean rocks--mainly quartzite and basalt--along this corridor that are consistent with "rift-related" activity.
Hartlaub analysed and dated the rocks before determining that the Murmac Bay Group is evidence of a failed rift in the ancient continent that has been named Nunavutia. He estimates the continent was larger than England, France and Germany combined. However, the researchers don't know yet if rifting succeeded in splitting any part of Nunavutia to form an ocean basin.
In studying the Murmac Bay Group, the researchers also discovered minerals in northern Saskatchewan that are 3.9 billion years old, and they've found rocks in the same area that date back 3.1 billion years. Heaman noted that these are some of the oldest minerals ever discovered. (In 1989, Dr. Sam Bowring of the Massachusetts Institute of Technology (MIT) found the oldest rock ever discovered on Earth, dating back four billion years, in Canada's Northwest Territories.)
Aside from the significance of the discovery to researchers trying to understand Earth's history and evolution, minerals this old will certainly draw the attention of people in the diamond exploration industry, Heaman said.
"Virtually all diamond deposits come from areas where you can find ancient crust preserved, such as we've found in northern Saskatchewan," he added.
"It's really exciting to find evidence of this large, ancient continent and these ancient crustal processes," Hartlaub said. "Our next step is to analyse the geochemical signatures of the minerals we've found to see if we can get an even better idea of what our Earth looked like more than two-and-a-half billion years ago."
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