UNITING THE PLATES OF AMERICA: PALEOMAGNETIC SIGNATURE OF THE HUDSONIAN OROGENY

With the oldest sutures of Laurentia found on the margins of the Slave craton, its assembly, and that of larger supercontinent Nuna, can be paleogeographically reconstructed by generating Slave paleopoles of Orosirian age (2050-1800 Ma). An abundance of poles exist for early and particularly late Orosirian time, defining the so-called Coronation loop; however few poles exist in between. We identify a radiating mafic dike swarm comprised of two north and northeast subswarms that intruded the southeastern Slave craton at overlapping ages of 1900 Ma with a focal point of a suspected plume center along the Taltson magmatic arc. Paleomagnetic data paired with U-Pb geochronology (baddeleyite) for this ‘Hearne’ dyke swarm offers paleogeographic constraints for the missing middle Orosirian interval. The virtual geomagnetic poles for the two subswarms, both confirmed with positive baked contact tests, are similarly distributed along coplanar swaths with which we apply Bingham statistics. The subswarms cannot be distinguished paleomagnetically, consistent with the plume interpretation of coeval, radiating intrusion. The only known process rapid enough to give rise to coplanarity in virtual geomagnetic poles on the time scale of a ~1-10 Myr intrusive event is true polar wander, if exceedingly rapid (>>1˚ Myr^-1). The long-axis of the bivariate Hearne pole lies at a angle to the established Coronation loop, implying a radically different position of the Slave craton relative to Earth’s minimum moment of inertia at 1900 Ma than before and after. Assuming the long-term stability of a true polar wander axis, kinematic plate motions can be deduced by rotating paleopoles and associated great-circle axes into alignment. The near-coincidence of Early and Late Orosirian paleogeographies implies that plate motions may be systematically related to the true polar wander reference frame. Compared to tectonic standstills of early and late Orosirian times, the Slave craton experienced two equally rapid 40˚ tectonic motions before and after intrusion of the Hearne dykes. The sudden shift in direction of plate motion correlates with the Snowbird phase of the Hudsonian orogeny. The suturing of Laurentia was locally associated with the fastest known rate of plate motion (~30 cm yr^-1) and was accompanied by rapid true polar wander.