CHRONOSTRATIGRAPHY OF MIDCONTINENT RIFT VOLCANICS PROVIDES NEW INSIGHTS INTO RIFT DEVELOPMENT AND THE RATE OF RAPID PALEOGEOGRAPHIC CHANGE

Through integrating high-precision U-Pb zircon geochronology with a compilation of existing and new paleomagnetic data, we develop an updated chronostratigraphy and magnetostratigraphic framework for the volcanics of the Midcontinent Rift. This framework allows for the correlations between volcanics across the Midcontinent Rift to be tested and improved thereby constraining temporal pulses of magmatism, the timing of unconformities associated with rift development and the overall duration of rift magmatism. Furthermore, analysis of temporally constrained paleomagnetic poles show with high confidence that the motion of Laurentia exceeded 20 cm/year, that it likely exceeded 25 cm/year and that it may have been as fast as 30 cm/year. This rate is faster than the maximum plate speed of India of ca. 17 cm/year as it rapidly approached Eurasia in the lead-up to Himalayan orogenesis. The onset of rapid motion can be explained as the result of a slab avalanche that also drove upwelling leading to prolonged magmatism in the Midcontinent Rift. This rapid subduction led to collisional orogenesis along the leading margin of Laurentia — an important step in the assembly of the supercontinent Rodinia. The protracted collision of the Grenvillian orogeny could have been sustained by the strong convective cell established as Laurentia moved southward.