LATE MESOPROTEROZOIC TECTONIC HISTORY OF LAURENTIA AND THE ASSEMBLY OF RODINIA (Invited Presentation)

The late Mesoproterozoic was a time of large-scale tectonic activity both in the interior and along the margins of Laurentia—notably the development of the Midcontinent Rift and the Grenvillian orogeny. A new compilation of paleomagnetic poles associated with the Midcontinent Rift coupled to new high-precision U-Pb geochronology reveals with high confidence that the motion of Laurentia exceeded 20 cm/year from 1110 to 1080 Ma in the lead-up to the Grenvillian orogeny. A novel Bayesian approach to invert the apparent polar wander path reveals that while some of this motion could be associated with true polar wander, rapid differential plate motion is required to explain the path. We propose that an avalanche of subducted slab material that drove fast plate motion invigorated mantle upwelling which was expressed as prolonged Midcontinent Rift volcanism. This rapid subduction led to collisional orogenesis along the leading margin of Laurentia—an important step in the assembly of the supercontinent Rodinia. The prolonged collision within the Grenvillian orogeny between ca. 1090 and 980 Ma was likely sustained due to this strong convective cell. The implied consumption of subducting oceanic lithosphere leading up to the Grenvillian orogeny is inconsistent with models wherein the conjugate craton to Laurentia's present-day eastern margin (typically taken to be Amazonia) arrives via sinistral translation. Subsequent positioning and configuration of Rodinia strongly hinges on the reconstruction of Baltica with Laurentia and associated interpretation of the Grenville and Sveconorwegian pole loops. Additionally, divergent interpretations of the Grenville loop pole path as representative of cratonic Laurentia or the result of translation of allochthonous terranes need to be resolved to advance Rodinia reconstructions. These contrasting hypotheses motivate future efforts to extend late Mesoproterozoic data sets from Laurentia's interior.