A young, thin subducted slab has excess density relative to the surrounding mantle…

PHYSICS · Subjective · Fermi University Physics · Earth, Climate & Energy Physics · Seismology, tectonics and geodynamics · Seismology, tectonics and geodynamics

The Solid Earth, Ch Plates, creep and convection: the mantle in motion

Problem

A young, thin subducted slab has excess density Δρ=60 kg m−3\Delta\rho = 60\,\mathrm{kg\,m^{-3}} relative to the surrounding mantle and thickness hslab=80 kmh_{\rm slab} = 80\,\mathrm{km}. Take g=10 m s−2g = 10\,\mathrm{m\,s^{-2}} and an upper-mantle viscosity ηv=5×1020 Pa s\eta_v = 5\times10^{20}\,\mathrm{Pa\,s}. Estimate the sinking-speed scale Δρghslab2/ηv\Delta\rho gh_{\rm slab}^2/\eta_v before any geometric factor for slab dip or width is included, expressing the result in mm yr−1\mathrm{mm\,yr^{-1}}.

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