Flexural rigidity of Fennoscandia inferred from the postglacial uplift

Abstract

The Earth's response to glacial loading/unloading offers exceptional promise for the study of the physical properties of the lithosphere. In particular, tilting of paleoshorelines is very sensitive to the lithosphere rigidity. To determine the flexural rigidity, the isostatic response to deglaciation in Fennoscandia is modeled using an Earth model with a layered mantle viscosity overlain by an elastic lithosphere. The flexural rigidity and asthenosphere viscosity is allowed to vary to get a match between theoretical and observed present rate of uplift and tilting of paleoshorelines. Five different ice thickness models are used. For a relatively thin ice (2500 m in central areas) the resulting flexural rigidity is more or less uniform over Fennoscandia, with a value of 1023 N m (elastic thickness te ≈ 20 km). This is regarded as minimum for the flexural rigidity of central Fennoscandia. The pattern of the present rate of uplift and the tilts of the paleoshorelines of the area also sets an upper bound of the flexural rigidity, 2.5 × 1025 N m (te ≈ 110 km) in more central areas of Fennoscandia. The flexural rigidity at the western coast of Norway does not seem to exceed 1023 N m (te ≈ 50 km). The most likely glacier model gives a flexural rigidity of 1023 N m (te ≈ 20 km) at the Norwegian coast, increasing to above 1024 N m (te ≈ 50 km) in central parts of Fennoscandia.