Lithosphere-asthenosphere system in shield areas of North America and Europe

In previous papers surface dispersion data have been combined with the results of deep seismic refraction data to derive a regionalization of the lithosphere-asthenosphere system and to investigate the presence of significant heterogeneity down to depths of 350 km along two profiles in the North European Fennoscandian area; a regionalized upper mantle model for the whole area down to more than 400 km is given as cross sections. We have extended that approach to North America. The older part of the shield shows lid thickness up to more than 100 km with, if any, weak shear velocity contrast to the underlying layer. The surrounding areas are characterized by a thinner lid; a stronger low-velocity zone to lid contrast may be found in peripheral areas. A map of the lithosphere-asthenosphere system has been derived, permitting a better regional resolution of the shear-wave velocity distribution with depth beneath different regions of North America. The correlation between the lithosphere-asthenosphere system structure and other geophysical data is commented as well as the results for North America and those obtained for the corresponding North European area, in order to outline the geophysical characteristics of shield areas that might give useful constraints for the geodynamic behaviour of the plates to which they belong.