Thinning of the lithosphere by small-scale convective destabilization

Gravitational, topographical and seismological studies of uplift regions around hot spots on oceanic,^1,2 and continental plates^3-7 have suggested that considerable lithospheric thinning has taken place beneath these areas. Previous models used to study this phenomenon have been based on thermal conduction^8-11 and on the dynamic interaction between large-scale plume structures¹² and the lithosphere, for a purely temperature-dependent viscosity. However, their predictions of the time scale for direct erosion¹² of the lithosphere by these upwellings are too long. We propose here a new dynamical mechanism which works most efficiently for a temperature and pressure-dependent rheology. Our idea is that thinning of the lithosphere is accomplished by strong secondary convection enhanced by the presence of a low-viscosity zone which grows from a plume associated with a hot spot. This process is capable of producing the rapid time scale of the swell uplift¹³, of the order of 10 Myr, and the rates of thinning, of order 10 km Myr^-1, required by both geophysical^13,14 and geochemical¹⁵ observations.