Coupled Evolution of Plate Tectonics and Basal Mantle Structure
Geochemistry, Geophysics, Geosystems
The relationships between plate motions and basal mantle structure remain poorly understood, with some models implying that the basal mantle structure has remained stable over time, while others suggest that it could be shaped by the aggregation and dispersal of supercontinents. Here we investigate the evolution of mantle flow driven by end-member plate tectonic models over 1 Gyr. We implement a tectonic scenario in which supercontinent reassembly occurs by introversion, and consider three distinct references frames that result in different net lithospheric rotation. Our flow models predict a dominant degree-2 mantle structure most of the time. We analyze the relationship between imposed tectonic velocities and deep mantle flow, and find that at spherical harmonic degree 2, the maxima of lower mantle radial flow and temperature follow the motion path of the maxima of surface divergence. It may take ∼160–240 Myr for lower mantle structure to reflect plate motion changes when the lower mantle is reorganized by slabs sinking onto basal thermochemical structures, and/or when slabs stagnate in the transition zone before sinking to the lower mantle. Basal thermochemical structures move at less than 0.6°/Myr in our models, with a temporal average of 0.16°/Myr when there is no net lithospheric rotation, and between 0.20 and 0.23°/Myr when net lithospheric rotation exists and is induced in the lower mantle. Our results suggest that basal thermochemical structures are not stationary, but rather linked to global plate motions and plate boundary reconfigurations, reflecting the dynamic nature of the coevolving plate-mantle system.
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