FLEXURAL RIGIDITY OF FENNOSCANDIA INFERRED FROM THE POSTGLACIAL UPLIFT

The Earth's response to glacial loading/unloading offers exceptional p romise for the study of the physical properties of the lithosphere. In particular, tilting of paleoshorelines is very sensitive to the litho sphere rigidity. To determine the flexural rigidity, the isostatic res ponse to deglaciation in Fennoscandia is modeled using an Earth model with a layered mantle viscosity overlain by an elastic lithosphere. Th e flexural rigidity and asthenosphere viscosity is allowed to vary to get a match between theoretical and observed present rate of uplift an d tilting of paleoshorelines. Five different ice thickness models are used. For a relatively thin ice (2500 m in central areas) the resultin g flexural rigidity is more or less uniform over Fennoscandia, with a value of 10(23) N m (elastic thickness te approximate to 20 km). This is regarded as minimum for the flexural rigidity of central Fennoscand ia. The pattern of the present rate of uplift and the tilts of the pal eoshorelines of the area also sets an upper bound of the flexural rigi dity, 2.5 x 10(25) N m (te approximate to 110 km) in more central area s of Fennoscandia. The flexural rigidity at the western coast of Norwa y does not seem to exceed 10(23) N m (te approximate to 50 km). The mo st likely glacier model gives a flexural rigidity of 10(23) N m (te ap proximate to 20 km) at the Norwegian coast, increasing to above 10(24) N m (te approximate to 50 km) in central parts of Fennoscandia.