Upper Proterozoic paleomagnetic poles from Laurentia and the history of the Grenville Structural Province

Paleomagnetic poles from the Precambrian shield of North America (Laurentia) for the interval −1500 to −600 m.y. are reviewed. The results are best explained by assuming that the path(s) of apparent polar wander had the form of a sequence of loops with amplitudes of about 60° and period of 200–300 m.y. It is possible that such polar paths are the signature of the Wilson cycle, the cycle of opening and closing oceans. The presence of such loops does not imply that this cycle necessarily operated but only that their presence is consistent with its operation during the later Proterozoic. Many pole determinations are now available from medium- to high-grade metamorphic terrain of the Grenville structural province, and the poles from that part of the province (Grenvillia) not immediately adjacent to the Grenville front are statistically distinct from the poles from the remainder of Laurentia (Interior Laurentia). Three hypotheses have been invoked to explain this fact, and a fourth is added here. Only hypotheses 1 and 2 adequately explain the paleomagnetic data. Hypothesis 2 requires rapid drift of Laurentia at rates of 20 cm/yr for about 200 m.y. Hypothesis 1 requires that at −1150 m.y., Grenvillia was displaced 5000 km from Interior Laurentia and approached and became sutured to it at about −1000 m.y., the Laurentian shield as we know it today being formed.