...“The volcanic rocks are remnants of what is called the Midcontinent Rift, and it is an enormous geological puzzle. Rifts are wounds in Earths outer layer that can grow to eventually form new oceans. That is how the Atlantic Ocean got its start some 200 million years ago, and an active rift continues to widen that basin. But the Midcontinent Rift was different. It opened a 3,000-kilometre crack in North America and created a basin as big, perhaps, as the Red Sea — then the system shut down. The wound stopped growing and the continent remained intact. “How that feature could just totally reorganize the crust of the Earth in the Lake Superior region and not manage to break the continent apart is fairly amazing,” says G. Randy Keller, a geophysicist at the University of Oklahoma in Norman and director of the Oklahoma Geological Survey. “Its a spectacular failure.” And a forgotten one, too. The rift is mostly buried under thick sediments, which makes it hard to study. And it lies far from the continents attention-grabbing geological features, such as mountain belts and earthquake zones. “For a long time, the rift has been a very neglected thing,” says Peter Hollings, a geochemist at Lakehead University in Thunder Bay, Canada. That is now changing. Geologists have started to flock to the region to explore the enormous deposits of ore minerals left by volcanic activity during the creation of the rift: one area in northern Minnesota, for example, is the largest untapped copper–nickel deposit in the world. Another source of interest has come from the US National Science Foundations EarthScope project and related programmes, which installed dozens of temporary seismometers across the rift to provide an unprecedented picture of Earths crust and upper mantle there. . . .
Posted on: Wed, 04 Dec 2013 18:45:47 +0000