Upper Mantle Viscosity Determined from Stokes's Law

Abstract

ONE of the more important properties required for testing theories of mantle convection and plate tectonics is the effective viscosity of the upper mantle. Measurements of viscosity have been obtained from the seismic behaviour of the upper mantle¹ and from the uplift of land during postglacial recovery^2,3. Because these methods involve either time scales different from those of plate tectonics or rather complex model studies, the values obtained are not necessarily directly applicable to plate tectonic theory. The new determination which we describe here is direct. It gives the effective viscosity of the upper mantle between depths of 250 and 600 km, and over a period of nearly 4 m.y.