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| 2. |
- Cherevatova, M., et al.
(författare)
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Magnetotelluric array data analysis from north-west Fennoscandia
- 2015
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 653, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- New magnetotelluric (MT) data in north-west Fennoscandia were acquired within the framework of the project "Magnetotellurics in the Scandes" (MaSca). The project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable Precambrian cratonic interior to passive continental margin beneath the Caledonian orogen and the Scandinavian Mountains in western Fennoscandia. An array of 59 synchronous long period and 220 broad-band MT sites was occupied in the summers of 2011 to 2013. We estimated MT transfer functions in the period range from 0.003 to 10(5) s. The Q-function multi-site multi-frequency analysis and the phase tensor were used to estimate strike and dimensionality of MT data. Dimensionality and strike analyses indicate generally 2-D behaviour of the data with 3-D effects at some sites and period bands. In this paper we present 2-D inversion of the data, 3-D inversion models are shown in the parallel paper. We choose to invert the determinant of the impedance tensor to mitigate 3-D effects in the data on our 2-D models. Seven crustal-scale and four lithospheric-scale 2-D models are presented. The resistive regions are images of the Archaean and Proterozoic basement in the east and thin Caledonian nappes in the west. The middle and lower crust of the Svecofennian province is conductive. The southern end of the Kittila Greenstone Belt is seen in the models as a strong upper to middle crustal conductor. In the Caledonides, the highly conductive alum shales are observed along the Caledonian Thrust Front. The thickest lithosphere is in the Palaeoproterozioc Svecofennian Domain, not in the Archaean. The thickness of the lithosphere is around 200 km in the north and 300 km in the south-west.
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| 3. |
- Bock G., Roberts R.G., Kissling E., Achauer A., Alingahi J., Bruneton M., Friedrich W., Grad M. Guterch A., Hjelt S-E., Hyvönen T., Ikonen J-P., Komminaho K., Korja A, Heikkinen P., Kozolovaskaya E., Nevsky M.V., Pavlenkova N., Pedersen H., Plomerova J.
(författare)
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Seismic probing of Archean and Proterozoic Lithosphere in Fennoscandia.
- 2001
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Ingår i: EOS Transactions American Geophysical Union. - : American Geophysical Union. ; 82, s. 621,628-629
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Tidskriftsartikel (refereegranskat)
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| 4. |
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| 5. |
- SVEKALAPKO Seismic Tomography Working Group (SSTWG): G. Bock, U. Achauer, A. Alinaghi, J. Ansorge, M. Bruneton, W. Friederich, M. Grad, A. Guterch, S.-E. Hjelt, T. Hyvönen, J.-P. Ikonen, E. Kissling, K. Komminaho, A. Korja, P. Heikkinen, E. Kozlovskaya, M
(författare)
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Seismic probing of Fennoscandian Lithosphere
- 2002
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Ingår i: EOS, Trans. Am. geophys. Un.. ; 82:621, s. 628-629
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Tidskriftsartikel (refereegranskat)
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| 6. |
- Buntin, Sebastian, et al.
(författare)
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Emplacement and 3D geometry of crustal-scale saucer-shaped intrusions in the Fennoscandian Shield
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Saucer-shaped intrusions of tens of meters to tens of kilometres across have been observed both from surface geological mapping and geophysical observations. However, there is only one location where they have been reported to extend c. 100 km laterally, and emplaced both in a sedimentary basin and the crystalline basement down to 12 km depth. The legacy BABEL offshore seismic data, acquired over the central Fennoscandian Shield in 1989, have been recovered and reprocessed with the main goal of focusing on this series of globally unique crustal-scale saucer-shaped intrusions present onshore and offshore below the Bothnian Sea. The intrusions (c. 1.25 Ga), emplaced in an extensional setting, are observed within both sedimentary rocks (<1.5 Ga) and in the crystalline basement (>1.5 Ga). They have oval shapes with diameters ranging 30-100 km. The reprocessed seismic data provide evidence of up-doming of the lower crust (representing the melt reservoir) below the intrusions that, in turn, are observed at different depths in addition to a steep seismically transparent zone interpreted to be a discordant feeder dyke system. Relative age constraints and correlation with onshore saucer-shaped intrusions of different size suggest that they are internally connected and fed by each other from deeper to shallower levels. We argue for a nested emplacement mechanism and against a controlling role by the overlying sedimentary basin as the saucer-shaped intrusions are emplaced in both the sedimentary rocks as well as in the underlying crystalline basement. The interplay between magma pressure and overburden pressure, as well as the, at the time, ambient stress regime, are responsible for their extensive extent and rather constant thicknesses (c. 100-300 m). Saucer-shaped intrusions may therefore be present elsewhere in the crystalline basement to the same extent as observed in this study some of which are a significant source of raw materials.
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| 8. |
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| 9. |
- Vanyan, L.L., Kuznetsov, V.A., Lyubetskaya, T.V., Palshin, N.A., Korja, T., Lahti, I. and the BEAR Working Group
(författare)
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Electrical Conductivity of the Crust beneath Central Lapland
- 2002
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Ingår i: Izvestiya, Physics of the Solid Earth. ; 38:10, s. 798-815
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Tidskriftsartikel (refereegranskat)
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| 10. |
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| 11. |
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| 12. |
- Autio, U.A., et al.
(författare)
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Magnetotelluric array in the central Finnish Lapland II : 3-D inversion and tectonic implications
- 2020
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Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 794
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Tidskriftsartikel (refereegranskat)abstract
- The northern part of the Fennoscandian shield records several Palaeoproterozoic phases of rifting, crustal shortening, metamorphism and structural reactivation. The geologic history has left behind a complex crustal geoelectric structure as evidenced by magnetotelluric (MT) data from the central Finnish Lapland acquired in the context of the MaSca-project in 2014. The data are characterized by strong 3-D effects such as high phase tensor skew values and anomalous induction vectors. Interestingly, however, at the same time a dominant E-W principal direction from the phase tensor data can be inferred. 3-D conductivity models derived using the ModEM code display, high crustal conductance (> 10,000 S) in the vicinity of the Central Lapland Greenstone Belt, the Peräpohja Belt and the Kuusamo Belt. Conductors in the northern and southern part of the study area are separated by a resistor coinciding with the Central Lapland Granitoid Complex. A remarkable feature is an arc-shaped conductor inside the northern part of the Central Lapland Granitoid Complex, which continues into the Central Lapland Greenstone Belt in the north. The conductor is associated with a major induction vector anomaly and also coincides with extreme responses (negative phase tensor principal values), which are discussed in an accompanying paper. The conductive structures in the models are interpreted as deeply buried graphite and sulphide bearing metasedimentary rocks or as reactivated Archaean shear zones. The revealed geoelectric structures also partly correlate with seismic reflection and other geophysical data from the area. A possible explanation for the observed pervasive E-W principal direction of the phase tensor data could be the aulacogen (failed rift) suggested in recent tectonic evolution models.
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| 13. |
- Nikkila, K., et al.
(författare)
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Analog modeling of one-way gravitational spreading of hot orogens - A case study from the Svecofennian orogen, Fennoscandian Shield
- 2015
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 268, s. 135-152
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Tidskriftsartikel (refereegranskat)abstract
- Geodynamic models offer insight into deformation styles of syn- and post-collisional extensional processes. Such models often ignore the effect of lateral viscosity contrast between accreted terranes and inherited tectonic boundaries. This paper presents a set of crustal-scale analog experiments of one-way post-collisional gravitational spreading testing the effect of crustal heterogeneity by using two mechanically contrasting blocks, pre-existing cuts with varying dips, and three layers with contrasting rheologies. Two blocks represent strong, mature, and weak, juvenile crustal parts. Both blocks have three horizontal crustal layers: brittle upper, weak partially molten middle and dry strong lower layer. Cuts represent pre-existing crustal-scale shear zones and tectonic boundaries. The experiments indicated that tectonic boundaries may facilitate exhumation and increase extensional strain, when the boundaries dip opposite to the flow direction. The tectonic boundaries may also split and divide the crust into separate blocks with independent deformation signatures: shortening, elongation or rotation. The tectonic boundaries rotated along vertical axes toward the flow direction. The modeling results suggest that in areas with inherited tectonic boundaries and compositional differences the amount of extension is unevenly distributed between the different parts during the widespread unilateral gravitational spreading and that the flow has different effects on the contrasting crustal units, in both lateral and vertical directions. To validate the modeling, the results are compared to geophysical and geological data from the Paleo-proterozoic Svecofennian orogen in the Fennoscandian Shield. The comparison suggests that the orogen underwent 50% extension and was thinned by maximum of 20% via westward gravitational spreading. This spreading rotated the crustal-scale blocks, shear zones and tectonic contacts. It also brought exhumed, high grade middle crustal blocks into contact with subsided, low grade, upper crustal blocks. We suggest that results of the analog models can be used as proxies in both ancient and modern hot accreted orogens, which have undergone post-convergence continental mid-crustal weakening and have comprised of juxtaposed terranes with varying rheological compositions.
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