Electronic Resource
Oxford, UK
:
Blackwell Publishing Ltd
Geophysical journal international
116 (1994), S. 0
ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
Electrical properties of the crust in the central Fennoscandian (Baltic) Shield are examined along the 435 km magnetotelluric profile SVEKA. A 2-D geoelectric model shows large variations in the crustal resistivity with the model resistivities ranging from 0.1 to 35 000 Ωm. The main geoelectrical features of the crust and upper mantle are: (1) a resistive Archaean lower crust (conductance ≤30 S). (2) A conductive Palaeoproterozoic lower crust beneath the Central Finland Granitoid Complex (170-900S). Free H2O-rich fluids trapped into the lower crust seem less plausible causes for enhanced conductivity as long retention times are required and no possible sources seem to be available to produce fluids into the dry lower crust. Most likely causes for permanent enhancement of lower crustal conductivity include the conductive fill of ductile shear zones, conductive graphite-bearing lamellae, conduction in mafic rocks perhaps via conduction in magnetite, or conductive solid remnants of an ancient shear zone between two crustal blocks. Thin graphitic grain-boundary films precipitated from CO2-rich fluids also seem less plausible. (3) A very resistive (10 000-35 000 Ωm) upper crust of the Palaeoproterozoic Central Finland Granitoid Complex and the Archaean Domain. (4) Narrow and elongated conductors (0.1-100 Ωm) beneath the Palaeoproterozoic Kainuu (KSB) and Tampere (TSB) Schist Belts are caused by graphite-bearing metasedimentary rocks buried deep into the crust in the collisions of crustal terranes during the formation of the Palaeoproterozoic Svecofennian crust. The 500 km long TSB conductor represents an internal Svecofennian terrane boundary whereas the KSB conductor is a part of a discontinuous Archaean-Proterozoic boundary conductor. (5) Resistive upper mantle. There are no indications of an upper mantle conducting layer within the uppermost 300 km in the central part of the Fennoscandian Shield.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1994.tb02135.x
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