T42B-07:
The Role of Subduction and Mantle Plumes in the Supercontinent Cycle
Thursday, 18 December 2014: 11:50 AM
Philip J Heron, University of Toronto, Earth Sciences, Toronto, ON, Canada, Julian Philip Lowman, University of Toronto, Toronto, ON, Canada and Claudia Stein, University of Münster, Münster, Germany
Abstract:
Several processes unfold during the supercontinent cycle, more than one of which might result in an elevation in subcontinental mantle temperatures through the generation of mantle plumes. Geodynamic modeling motivated by paleogeographic plate reconstructions has indicated that subcontinental mantle upwellings appear below large continents that are extensively ringed by subduction zones. Moreover, several numerical simulations of supercontinent formation and dispersal show that the genesis of subcontinental plumes follows the formation of subduction zones on the edges of the supercontinent, rather than resulting from continental thermal insulation. However, the influence of the location of mantle downwellings on the position of subcontinental plumes has received little attention. Using 2D and 3D numerical mantle convection models, featuring geotherm- and pressure- dependent viscosity profiles with thermally and mechanically distinct oceanic and continental plates, we examine the evolution of mantle dynamics after continental accretion at a subduction zone (as occurred during the formation of Pangea). In simulations of vigorous mantle convection, we consider a range of supercontinent areas and change the upper and lower mantle viscosity contrast to determine their relation to plume formation. The results presented show that the formation of subduction zones at the margins of a supercontinent has a profound effect on mantle dynamics, and may help to explain how the sites of previous (and future) large igneous provinces were (or will be) determined. Subcontinental plume locations for all viscosity profiles show varying degrees of dependence on the location of continental margin subduction post-supercontinent formation. Furthermore, we find that changing the viscosity structure for mantle convection simulations (with similar surface heat flux) can determine the position (and number) of subcontinental plumes penetrating the upper mantle post-supercontinent formation.
