No. 49: Jan-Feb 1987
The NACP (North American Central Plains) electrical conductivity anomaly snakes west from Hudson Bay, then south into the States, and wiggles a bit before terminating in Wyoming. As delineated by magnetic surveys, it is over 2000 kilometers long, and may be longer and wider than shown on the map. Since the top of this belt of high electrical conductivity rock is some 10 kilometers below the surface, no one is sure of its constitution -- graphite in schistose rocks is one guess. Its mean-ing for the geology of North America is also a mystery -- it could be the edge of a buried tectonic plate. Whatever it is, it is important: "the largest and most enigmatic continental-scale structure discovered to date by electromagnetic induction studies."
(Jones, Alan G., and Savage, Peter J.; "North American Central Plains Conductivity Anomaly Goes East," Geophysical Research Letters, 13:685, 1986.)
|The crosshatched regions represent the NACP anomaly. Triangles, dots, crosses, and MT signify magnetometer stations and surveys.|