Comparison of crustal structure along DSS profiles in SE Fennoscandia

Abstract

SUMMARY main features of the crustal structure of the Karelian and Svecofennian provinces are discussed on the basis of data obtained from deep seismic sounding (DSS) profiles across the SE Fennoscandian Shield. The data show that in the ancient Karelian province the crust is thinner (about 40 km), the average velocity is lower (about 6.4kms-l) and the Moho boundary is a sharp discontinuity which produces strong reflections. The high-velocity layer in the lower crust, if it exists at all, is thin. In the younger Svecofennian province, crustal thickness averages about 45 km with a velocity of 6.6-6.8 km s-'. The reflectivity of the Moho is usually weak and a high-velocity layer with velocities greater than 7 km s-' is ubiquitous in the lower crust. High velocities in the lower crust and upper mantle are found in deep Moho areas. Beneath the younger granitic intrusions, Gothian complex and Vyborg Rapakivi granites, the crust is thinner than on average.