Electrical Conductivity of the Lithosphere- Implications for the Evolution of the Fennoscandian Shield
The electromagnetic induction research on the deep structure in the Fennoscandian Shield and the airborne surveys in Finland have provided a globally unique electromagnetic data set to estimate lithospheric conductivity. The data allow to focus from shield-scale structures to small local structures,...
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| Format: | Text |
| Language: | English |
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1996
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.501.5176 http://www.geophysica.fi/pdf/geophysica_1997_33_1_017_korja.pdf |
| Summary: | The electromagnetic induction research on the deep structure in the Fennoscandian Shield and the airborne surveys in Finland have provided a globally unique electromagnetic data set to estimate lithospheric conductivity. The data allow to focus from shield-scale structures to small local structures, and enables to interpret the conductivity structures in terms ranging from tectonic processes affecting the entire shield to small processes responsible for enhanced electrical conductivity within shear zones. The Shield is characterized by elongated belts of conductors that are limited to the upper half of the crust except for some occasional penetrations into the lower crust. Due to the large conductances involved and the correlation with the surface geology the primary conductivity mechanism invoked to explain this is electronic as found in graphite- and sulphide-bearing rocks. The conductive belts surround more resistive blocks and mark boundaries between distinct crustal units. The resistive regions serve as transparent windows to probe deeper properties of the shield. The deep Palaeoproterozoic crust seems to be more conductive, in particular in the central part of the shield, than the Archaean lower crust. There are also an increasing amount of evidence that the lower crust and even the upper mantle may be electrically anisotropic. Studies in the Lapland Granulite Belt |
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