The continual shifting of continents has led to the theories that, as in the cases of Pangaea and Rodinia, many, if not all of our continents, were at one time or another connected. One particular theory evolving from this is the SWEAT theory, standing for southwestern United States and East Antarctica, which theorizes that the southwestern United States was at one time connected to East Antarctica.
John Goodge, an NSF-funded researcher with the Department of Geological Sciences at the University of Minnesota-Duluth, and his team published a paper that details findings that they believe add considerable weight to SWEAT.
Goodge and his team were conducting a search for rocks that might provide links to the composition of the underlying continental crust of Antarctica. "We were picking up boulders in the moraines that looked interesting," Goodge said. "It was basically just a hodge-podge of material."
One of the rocks that they picked up turned out to be, later, a very specific form of granite with, as Goodge describes it, "a particular type of coarse-grained texture." Chemical and isotopic tests conducted by the team in laboratories in the US revealed the boulder to have a chemistry "very similar to a unique belt of igneous rocks in North America" that stretches from what is now California eastward through New Mexico to Kansas, Illinois and eventually through New Brunswick and Newfoundland in Canada.
This particular belt of rocks is known to once have been part of Laurentia, a component of what was once Rodinia.
"There is a long, linear belt of these igneous rocks that stretches across Laurentia. But 'bang' it stops, right there at the (western) margin where we knew that something rifted away" from what is now the West Coast of the United States," Goodge said."It just ends right where that ancient rift margin is, and these rocks are basically not found in any other part of the world."
Goodge notes that there is no real alternative explanation for how the rock got to where it was, other than a once continental meet with southwestern United States. The rock had been, as Goodge describes it, “bull-dozed over from that interior region of Antarctica,” thanks to ice streams which slowly pushed rubble underneath them as they moved.
"This is first-rate work and a fascinating example of scientists at work putting together the pieces of a much larger puzzle," said Scott Borg, director of the division of Antarctic sciences in NSF's Office of Polar Programs. "Not only do the authors pull together a diverse array of data to address a long-standing question about the evolution of the Earth's crust during a critical time for biological evolution, but the research shows how the ideas surrounding the SWEAT hypothesis have developed over time."
Posted by Josh Hill.
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