HASKELL [1935] REVISITED

The Haskell [1935] value of 10(21) Pa s for mantle viscosity is a clas sic and enduring constraint on the rheology of the Earth's interior. W e revisit this inference using spherically symmetric, self-gravitating , Maxwell viscoelastic Earth models. Our inference is based on both fo rward and inverse analyses of decay times associated with uplift at tw o sites considered by Haskell, Angerman River, Sweden, and Oslo, Norwa y, rather than the raw relative sea level (RSL) data at these sites. W e demonstrate that predictions of the decay time associated with the A ngerman River data are insensitive to variations in both the late Plei stocene ice load history and the lithospheric thickness of the Earth m odel (the predictions at Oslo are sensitive to both these inputs), and hence decay times at this site provide a remarkably robust constraint on mantle viscosity. We derive a constraint on the ''average'' viscos ity of the mantle of 0.65 - 1.10 x 10(21) Pa s, where the ''average'' resolved by the data encompasses a region which extends from the base of the Lithosphere to a depth of near 1400 km. This indicates that man y previous analyses which have invoked the Haskell value of 10(21) Pa s as a constraint on the average upper mantle (i.e., above 670 km dept h) viscosity alone have misinterpreted the resolving power of the infe rence. Furthermore, our analysis indicates that a number of apparently contradictory inferences of viscosity based on Fennoscandian data sat isfy the new, rigorous, interpretation of the Haskell constraint. Fina lly, we demonstrate how the ambiguity in the upper mantle/lower mantle viscosity contrast associated with the Haskell ''average'' may be red uced by invoking decay time constraints estimated from RSL curves in H udson Bay. A preliminary inversion of decay times at Angerman River an d Richmond Gulf (in Hudson Bay) suggests a contrast of approximately a n order of magnitude between the average viscosities of the upper mant le and the top 1000 km of the lower mantle; however, a conclusive anal ysis in this regard must await the determination of consistent decay t ime estimates for the Hudson Bay region.