Testing Global Plate Motion Models using Dynamic Topography and Cratonic Vertical Motions Inferred from Thermochronology

Abstract:

Fundamental questions exist regarding the interactions between plate motions, mantle dynamics, and topographic change. Dynamic topography—normal traction at the base of the lithosphere from mantle convection—can induce vertical motions of continents far from plate margins. Geodynamic models provide an opportunity to test the effects of different plate motion models on the dynamic topographic evolution of continents. Cratonic regions within the interior of continents that have been largely insulated from plate margin tectonism have especially good potential to record the long wavelength (>1000 km) and low amplitude (few km) vertical motions from dynamic topography. Here we use a 3D model of thermochemical convection to predict the vertical motion history of the Canadian shield with two different plate motion models. We then compare the results with new thermochronologic studies across the shield that indicate much of it was buried under several km of early Paleozoic sedimentary rocks that were later denuded. Geodynamic models of mantle convection using surface velocities from two different plate motion models for the ~450-250 Ma interval make distinctly different predictions of early Paleozoic topographic change. One model (Scotese, 2001; Zhang et al., 2010) predicts a dynamic topographic low in the Canadian Shield from ~450-320 Ma, driven by subduction at the western and eastern margins of Laurussia (present coordinates), followed by a gradual increase in topography from ~320 Ma until present day. Another model (Domeier and Torsvik 2014; Matthews et al., 2016), predicts a dynamic topographic high from ~410-350 Ma, caused in part by a spreading center off the western margin of Laurussia (present coordinates) and less convergence than in the Scotese/Zhang model, followed by a low from ~350-250 Ma, and a return to higher topography after 250 Ma. To first order, the early Paleozoic topographic low of the Scotese/Zhang model provides a better match to the early Paleozoic burial phase of the Canadian shield than the high predicted by the Torsvik/Matthews model. We suggest that this strategy is a useful approach for calibrating mantle dynamic and plate motion models.