Title

Willy FJELDSKAAR (Tectonor, Stavanger, Norway), Aleksey AMANTOV (VSEGEI, Russia)

Tilted Norwegian post­glacial shorelines require a low viscosity asthenosphere and a weak lithosphere

Scandinavia is one of the key areas for research on glacial isostatic adjustment. Extensive modeling of the late­ and post­glacial rebound in Fennoscandia has been done over the recent years, but unfortunately the suggested Earth rheology varies a lot among the researchers. Most of the researchers argue for a significant viscosity change from upper to lower mantle, combined with a thick elastic lithosphere. We study 5 paleo shoreline gradients with various Earth rheology parameters and various deglaciation models. Shorelines from coastal Norway show significant tilt toward the more central parts of Fennoscandia. The observed shoreline gradients offer exceptional promise for the study of the physical properties of the Earths uppermost layers. Our modeling shows that best fit with the observed data is achieved with a 150 km thick lowviscosity asthenosphere with a viscosity of 1.3 X10¹⁹ Pa s above a uniform mantle of viscosity 10²¹ Pa s, and an effective elastic lithosphere thickness (T_e) of 30 km (flexural rigidity ~5 X10²³ Nm). In contrast, models with a significant viscosity increase from upper to lower mantle combined with a thick elastic lithosphere cannot explain the shoreline gradients observed at the Norwegian coast. We suggest that the shoreline gradient information needs to be taken into account in glacial isostatic adjustment modeling.
Keywords: isostasy, modeling, rheology, Holocene, glaciation, Fennoscandia, Norway.