Abstract
A high-resolution calculation of strongly time-dependent thermal convection in the upper mantle with non-Newtonian, temperature-dependent rheology shows that, for an effective Rayleigh number of around 10 6, extremely fast upwellings, at times exceeding 10 m/yr, can be generated a few hundred kilometers below the lithosphere. There is a clear separation of timescales between this fast jet and the more slowly convecting mantle. Within this fast vertical shear layer is embedded a thermal boundary layer with a width of the order of 50 km. The development of the fast non-Newtonian upwelling is characterized by the growth of the plume head to a large enough size, before the plume takes off rapidly at a depth of around 350 km. Upon impinging the base of the lithosphere, this fast plume thins the lithosphere and the flow then becomes a horizontally moving hot sheet, extending out for around 1000 km. This scenario is found to repeat itself at the same location about 10 Myr after the first plume impingement.
Published Version
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