Crustal thicknesses in Fennoscandia

Abstract

As a supplement to seismic profiling surveys, crustal thicknesses have been estimated for 1 1 Fennoscandian seismograph stations equipped with three-component long period instruments, using the so-called spectral ratio technique of Phinney. The largest Moho depths, of the order of 45 km, were found for stations located in the north-east areas of Norway and Sweden and in Finland, with a local maximum in the Bothnian Bay. The coastal area of south-east Norway and Zealand, Denmark exhibit crustal thicknesses in the range 28-33 km. The agreement between our results and those obtained by conventional refraction profiling is good, when this comparison is restricted to profiles of lengths 300 km or more, and when the associated crustal thickness estimate is averaged over the central parts of the profiles in question. Also, a comparison between our results and other available geophysical information gives that the oldest tectonic provinces of the Baltic Shield also are characterized by relatively modest heat flow, and exhibit the greatest crustal thicknesses. Post-glacial uplift data and large wavelength free air gravity data appear to be uncorrelated with crustal thickness. The same partly applies to Bouguer gravity anomalies, thus implying that the isostatic compensation mechanism in Fennoscandia is of both Airy and Pratt type.hboduction For a long time there has been and still is a considerable interest among geophysicists in Pennoscandia aimed at detailed mapping of local crustal structures. In this respect several Seismic profiling surveys have been undertaken, and the corresponding data and results have been repeatedly reinterpreted in terms of two, three and even four-layer crustal models. The various profiling surveys have also been summarized repeatedly (

A North Sea-southern Norway seismic crustal profile

“…Two structural models were proposed for this distance range. In order to keep the results presented here consistent with Kongsberg seismograph station data (Bungum et al 1980 find a Moho depth of 34km at Kongsbergsee Figs 1 and 6), preference should be given to model 1 in Fig. 10.…”

Guided wave propagation in laterally varying media -- II. Lg-waves in north-western Europe

“…The propagation path here is with a shallowing Moho, but with the path slightly obliquely t o the trend of the crustal thickness (Bungum, Pirhonen & Husebye 1980). As a result we have conditions of the type discussed in section 5 of Paper I and so we get transfer of energy from Rayleigh t o Love t o give significant transverse components to Lg.…”

Origin and geodynamic evolution of the Archean crust of eastern Finland

“…The average crustal thickness of this part of the Baltic shield is 45 km (Bungum et al 1980;Galganile 1982). The volume of grey gneisses can therefore be estimated as 11 X 10 6 km 3 .…”

“…Dotted lines are geotherms. (Bungum et al 1980;Calganile 1982) and represent enormous volumes of magmas. The genesis of these magmas necessitated partial melting of large volumes of mafic crust.…”