The Depths to Lithospheric Magnetic Sources under the Baltic Shield

Abstract

We present the results of studying the depths to lithospheric magnetic sources under the BalticShield and adjacent territories of the Russian Plate and the Scandinavian Caledonides. The depths have beencalculated from the global model of the lithospheric geomagnetic field EMAG2v3 by the centroid method.The minimum depths of the lower boundary of the lithospheric magnetically active layer (30–35 km) wereobtained under the frame of the Baltic Shield, that is, the Russian Plate, the northern and southern parts ofthe Scandinavian Caledonides, the maximum (45 km), under the Scandinavian Peninsula, in the west ofthe Svecofennian orogen and the Norrbotten craton. The rest of the territory of the Baltic Shield is characterizedby intermediate depths (38–45 km). Based on a comparison of our estimates of the depth of the lowerboundary of lithospheric magnetic sources with the currently available models of the distribution of the Mohodepth under the study area, it can be seen that for most of the Baltic Shield, the magnetically active layer of thelithosphere is located within the crust, with the exception of two areas under the Svecofennian orogen and theeastern part of the Kola Peninsula. This fact supports the hypothesis that the upper mantle has magnetic propertiesin regions where positive long-wave anomalies of the geomagnetic field are observed at satellite altitudes.The obtained results show that the western and eastern parts of the Kola Peninsula can differ not only in thevelocity structure of the crust and upper mantle, which has been previously established by various seismologicalmethods, but also in the magnetic properties of the upper mantle layer located directly under the crust.