A new tectonic map of the Precambrian basement beneath the Phanerozoic Williston Basin of central North America shows the Archean Superior craton separated from the Archean Churchill and Wyoming cratons by a broad region of mostly Proterozoic origin. Included in the Proterozoic terrain are the vestiges of two or more volcanic island arcs and associated fore-arc and back-arc basins. The North American Central Plains electrical conductor and related seismic low-velocity zones are explained by the presence of hydrated oceanic-type crustal material within the remnant back-arc basins and adjoining terrains. Using geological, geophysical, and geochronological data from the Williston Basin and exposed Canadian Shield, we derive a plausible plate-tectonic model for the Proterozoic evolution of this region.

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