FURTHER CONSTRAINING THE LATE MESOPROTEROZOIC KEWEENAWAN TRACK: HIGH PRECISION DATES LEAD TO HIGHER PRECISION RATES

The apparent polar wander path (APWP) developed from the ca. 1.1 Ga North American Midcontinent Rift, known as the Keweenawan Track, reveals a significant change in paleomagnetic pole position during the ca. 25 million year history of rifting. Whether this directional change is a progression associated with rapid plate motion can be answered with new and previously published paleomagnetic data from the succession of lava flows at Mamainse Point combined with new data from lava flows of the Osler Volcanic Group. These data reveal progressively decreasing inclination that is best explained by equatorward motion of Laurentia. Plate motion rates calculated with constraints from current geochronology and paleomagnetic data suggest rates exceeding 20 cm/yr at the start of the Keweenawan Track. To estimate the uncertainty on such rate estimates, we use a Monte Carlo simulation method that incorporates the uncertainty on both poles and dates. This method reveals an uncertainty envelope on these rate estimates from as low as 10 cm/yr to rates exceeding 30 cm/yr. New U-Pb geochronology on zircon isolated from samples within the North Shore Volcanic Group, demonstrates that it is now possible to obtain weighted-mean ²⁰⁶Pb/²³⁸U dates that are an order of magnitude more precise than existing age constraints. Pairing such high-precision dates with paleomagnetic data in stratigraphic context provides a way to significantly improve the precision of rate estimates. Given the centrality of the Keweenawan Track in reconstructions of Rodinia, improvements to the calibration of Laurentia's APWP provide an essential framework for improving paleogeographic models. With the recent discovery of additional large igneous provinces coeval with the development of the Midcontinent Rift, there is the potential for significant future advancement in the understanding of late Mesoproterozoic paleogeography.