| 1. |
- Dyrelius, D., et al.
(författare)
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Bergarters fysik
- 1985
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Ingår i: Geofysik. - Uppsala : Svenska fysikersamfundet. - 9186344285
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Bokkapitel (populärvet., debatt m.m.)
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| 2. |
- Elming, Sten-åke
(författare)
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A palaeomagnetic study of Svecokarelian basic rocks from northern Sweden
- 1985
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 107:1, s. 17-35
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Tidskriftsartikel (refereegranskat)abstract
- This palaeomagnetic investigation comprises basic rocks from six localities from the Svecokarelian zone in northern Sweden. Most of the pole positions in this study and other reported poles of Svecokarelian and post-Svecokarelian rocks fall within an approximately 12 degrees wide band running from east to west representing ages of magnetizations from 1880-1700 to ∼ 1530 Ma. Thermal demagnetizations of specimens of the probably oldest massifs indicate a possible backward continuation of the polar wandering path. Mineralogical studies of thin sections of the rocks show ore symplectites and myrmekitic textures indicating a slow rate of cooling at least at the end of the rock formation. Signs of metamorphism are demonstrated by the existence of secondary minerals, including magnetite, not related to late magmatic alterations. The distribution of site means as well as the change of directions of the remanence vectors during thermal demagnetization can be explained by a slow rate of cooling and where signs of metamorphism exist by partial remagnetization of the rock. This study has, apart from the palaeomagnetic results, demonstrated the difficulty of correlating radiometric ages with ages of magnetization
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| 3. |
- Elming, Sten-Åke
(författare)
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Geological modelling based on gravity data from the central part of the Swedish caledonides
- 1988
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 110:4, s. 317-327
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Tidskriftsartikel (refereegranskat)abstract
- Gravimetric measurements have been carried out within a c. 500 km2 area of western Jämtland in the Swedish Caledonides. Using different types of regional-residual gravity field separations, various geological models have been tested to fit the measured gravity data. Information on the geology and density of the rocks have reduced the number of possible models which are presented along two profiles. These models confirm the existence of antiforms and synforms running approximately parallel to the mountain range. The main profile crosses the two synforms over which positive anomalies are identified. Both in the western Tnnfors Synform and the eastern re Synform this is explained by the presence of high density Seve rocks, in the former case occurring beneath a cover of Kli Nappes. The depth to the base of the Seve Nappe units in the Tnnfors Synform is calculated at 4.5 km and in the re Synform at 3 km. The maximum depth to the interface between Kli and Seve rocks in the Tnnfors district is 3.2 km. Gravimetric models of the basement rocks in the windows, and difference in physical properties between the crystalline rocks of the windows and those of the autochthonous basement east of the Caledonian thrust front, imply that the basement exposed in the antiforms is allochthonous. A gravity minimum east of the re Synform is interpreted as a southern continuation of low density granites related to the Olden Complex. The inferred thickness of these low density rocks suggests that it may be a part of the autochthonous basement.
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| 4. |
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| 5. |
- Pesonen, L. J., et al.
(författare)
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Crustal evolution of Fennoscandia : palaeomagnetic constraints
- 1989
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 162:1-2, s. 27-49
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Tidskriftsartikel (refereegranskat)abstract
- Palaeomagnetic poles from Fennoscandia, ranging in age from Archaean to Tertiary, are compiled and graded using a modified Briden-Duff classification scale. An new "filtering" technique is applied to select only the most reliable poles for analysis. The filtering takes into account the following information: 1. (1) source block of rock unit,2. (2) age of rock,3. (3) age of magnetization component,4. (4) scatter of palaeomagnetic directions,5. (5) information from multicomponent analysis of natural remanent magnetization (NRM),6. (6) whether the pole considered belongs to a cluster or subcluster of poles,7. (7) magnetic polarity and8. (8) the author's original assignment of results.Data are still insufficient for the drawing of separate Apparent Polar Wander Paths (APWP) for different blocks or cratons of Fennoscandia. Treating Fennoscandia as a single plate, a new APWP from Archaean to Permian is constructed. From the five previously drawn APWP loops (or "hairpins"), only one, the Jatulian loop (2200-2000 Ma), disappears in filtering. The loops during 1925-1700 Ma and during 1100-800 Ma ago are linked to Svecofennian and Sveconorwegian orogenies, respectively. Palaeomagnetic data support the concept that these orogenies took place episodically; three distinct orogenic pulses (early, middle and late) can be distinguished in the cluster plots of palaeopoles. The drift history of Fennoscandia from Archaean to Permian is presented. During most of geological history, Fennoscandia has occupied low to moderate latitudes and undergone considerable latitudinal shifts and rotations. The Svecofennian and Sveconorwegian orogenies have different kinematic characteristics. During the Svecofennian orogeny, Fennoscandia drifted slowly while rotating a large amount in an anticlockwise sense. During the Sveconorwegian orogeny, it drifted rapidly and rotated first clockwise and then anticlockwise. The most striking feature in the drift velocity curves is, however, the pronounced maxima in the latitudinal drift and rotation rates (˜ 9 cm/yr and ˜ 0.8°/Ma, respectively) during the late Subjotnian-Jotnian anorogenic magmatism and rifting phase (˜1450-1250 Ma ago), possibly reflecting the passage of Fennoscandia across a thermal upwelling (hotspot) at equatorial latitudes. The use of palaeomagnetism in delineating and dating movements between blocks is demonstrated with three examples from the POLAR Profile area, the northernmost section of the European Geotraverse.
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| 6. |
- Widenfalk, Lennart, et al.
(författare)
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A multidisciplinary investigation of the Notträsk Gabbro, northern Sweden
- 1985
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 107:2, s. 109-126
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Tidskriftsartikel (refereegranskat)abstract
- The differentiated, sulfide-bearing gabbro near the city of Boden in northern Sweden has been investigated in order to get a plausible model for its formation, shape and age. The gabbro is associated with a major fault system along which several intrusive bodies occur. The largest of these has been traversed by a gravimetric, magnetometric and geological profile. The investigated intrusion is undeformed and oval-shaped and covers some 20 km2. The outer parts of the body consist of a norite in contact with older meatasediments and granites of varying age. Inside the norite occurs a magnetite-rich gabbro, which forms a ring around the centre of the massif, which in turn consists of leucogabbro-olivine gabbro. Fe, Ti and K are low in the centre where Mg and Cr have their highest contents. Impregnations of sulfides and a massive pyrrhotite vein with some 1 % Ni are located in the norite. A number of intrusion models have been tested by computer modelling combining gravimetric and magnetic field data. The most probable model seems to be a funnel-shaped body pointing downwards. The different gabbro types dip steeply inwards indicating vertical zones rather than horizontal. Palaeomagnetic measurements show that the intrusion has a similar orientation of magnetization as other gabbros of the Haparanda series in northern Sweden (1800-1900 Ga, Rb-Sr). Furthermore, the pole distributions show that the rock cooled slowly, which may indicate that the present outcrop is a deep part of an eroded intrusion. The massif is supposed to have been formed by a diapiric re-emplacement of primary horizontal cumulates formed in the sequence olivine gabbro-leucogabbro-magnetite-bearing gabbro-norite.
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