Science reports:

Along the eastern front of the Appalachian Mountains, buried just below the surface, lies a fragment of a lost continent. Running from Maine to Georgia, the 200-kilometer-thick slab of crust was probably created by volcanic eruptions during the breakup of the Pangaea supercontinent some 200 million years ago and later buried by silt from eroding mountains.

Known as the Piedmont Resistor, this piece of Pangaea is one of the signature discoveries of the Magnetotelluric (MT) Array, 1800 temporary stations scattered across the contiguous United States that measured the conductivity of deep rocks. Now, 20 years after it started, the MT Array has released its final map and model in a paper published today in Reviews of Geophysics. It shows how the assembly of the continent left hidden structures such as the Piedmont Resistor—and mineral riches. “You can see all the sutures,” says co-author Paul Bedrosian, a geophysicist at the U.S. Geological Survey (USGS). “And those boundaries, even though they’re a billion years old, are where you look for mineral resources.”

The MT Array “set a global standard,” says Hao Dong, a geophysicist at the China University of Geosciences, inspiring similar projects in China, Australia, and Brazil. Besides revealing the underpinnings of the continent, it has shown how geology can amplify the hazard solar storms pose to electrical grids. And it did so on a shoestring budget, costing only $20 million when adjusted for inflation, says Adam Schultz, a geophysicist at Oregon State University who previously led the project. “The quality of the data returned is a hell of a bang for a buck.” [Continue reading…]