| 1. |
- Enmark, Thomas, et al.
(författare)
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The Gallejaur intrusion in northern Sweden — a geophysical study
- 1983
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 105:4, s. 287-300
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Tidskriftsartikel (refereegranskat)abstract
- Geophysical and geological models of the Gallejaur structure in northern Sweden are presented. The plausibility of each of them is discussed. It is shown that the models so far suggested, as interpreted mainly on the basis of geological mapping, are not compatible with petrophysical studies combined with gravity and magnetic data. An alternative model of the Gallejaur structure based on combined geological, petrophysical and geophysical interpretation is suggested. The structure is interpreted as a large rounded mafic laccolith intrusion with a shallow cap of monzonite derived by differentiation at the top. The maximum depth extent of the structure is calculated to be about 3.5 to 4.5 kilometres.
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| 3. |
- Nisca, Dan H.
(författare)
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Nya litologiska-tektoniska modeller för regionen Västerbotten - södra Norrbotten
- 1995
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High quality bedrock and tectonic maps are the platform for locating natural resources such as ore, oil, gas, and water. Bedrock maps are also used in the design of large constructions, including highways, bridges, dams, power plants, tunnels, nuclear and other waste repositories. The main objective of the thesis is to improve and develop analysis and techniques for bedrock mapping mainly based on regional geophysics. The value of the improved approaches is demonstrated by constructing a lithologic-tectonic map for the Västerbotten - South Norrbotten region in northern Sweden. A fractal model has been adopted for the design and performance of the study. Instead of investigating an area of 50 km x 50 kin or smaller, a whole region or an area of 300 km x 250 has been studied. According to the fractal model, there are genetic connections between small and large geologic structures. The application of this model made possible: (a) the detection of structures, (b) establishing a genetic link between geologic structures and put them into large lithologic-tectonic relations and (c) a better understanding of the initiation, formation and development of different structures. The bedrock mapping is performed by integrating information provided by various sources: as a geoscientific multiand interdisciplinary analysis concept (MIA). Nine different main data sets have been used: (1) aeromagnetic data, (2) gravity data, (3) radiometric data, (4) satellite photo, (5) topography, (6) drainage system, (7) structural geologic map, (8) seismicity map and (9) esker map. For the interpretation a number of different visualizations of gravity data, aeromagnetic data and topographic data have been used. Besides the nine main data sets used in the neotectonic analysis, information on end moraines, highest coastline, isostatic uplift, seismotectonics, in situ stress measurements and documented late- to postglacial faults have been included. The enclosed sketch map shows the new tectonic "backbone" for the region. Some of the zones are defined as reverse faults/thrusts, e.g. the Malå-Skellefte Tectonic Zone (MSTZ) and the Knaften-Bureå Tectonic Zone (KBTZ). A large circular structure with a diameter of about 100 km, Lycksele Ring Structure (LRS), is defined in the central part of the region. Several graben-horst structures have been outlined in the northern part of the region. The so called "Nickelzonen" is interpreted as a dextral shear zone and it is renamed the Burträsk Shear Zone (BSZ). In the eastern part of the region a large scale fault zone, Krukmakar Fault Zone (KFZ) is defined. The major part of the bedrock west of the KFZ consists of granitoids while the eastern part consists mainly of migmatites. Cauldron structures have also been identified, e.g. the Gallejaure structure and the Jörngranite structure situated just north of the Skellefte field. The area between Urneå-Skellefteå or the Lövånger Tectonic Zone (LTZ) belongs to the localities in Sweden with the highest earthquake frequencies. In this thesis, tectonic models are presented for the LTZ, the Burträsk area (BSZ, KBTZ), the Skellefte valley (MSTZ), the Storavan area (horst-graben) and the central part of the study area (LRS). Some of the defined faults coincide with earthquakes and documented late- to postglacial faults, which indicates reactivations of very old weakness zones in the crust. Yet other major findings are: (1) initiation, formation and development of kursu valleys. This has been enigmatic for the last 100 years. It is now obvious, these valleys are caused by neotectonics and erosion. (2) Glaciations/deglaciations are considered to enhance fluid circulation in the crust. A hypothesis of glacial pumping is proposed to explain this process. (3) The interpretation of the tectonics in the study area shows that neotectonic faults are much more extensive than previously documented in the region. (4) The tectonic and neotectonic features recognized by this study are also compared with corresponding features in the central part of the Baltic Shield, e.g. they show large scale connections. The new bedrock mapping technique and the new lithologic - tectonic models presented in the thesis are of utmost consequence for future ore prospecting in the region and for investigations concerning the bedrock stability.
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| 4. |
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| 5. |
- Nisca, Dan H., et al.
(författare)
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The lycksele structure, a huge ring formation in Northern Sweden : result of an impact?.
- 2000
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Ingår i: S T A R (Online). - 1548-8837. ; 38
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The current database of impact structures in Fennoscandia reveals 28 proven impact craters of various ages and sizes. Recently, we started to search for large and old impact structures, which may show traces of the impact in their shape or in their rocks and minerals and which can be diagnostically identified through the masking effects of postimpact deformations. Since we are dealing with strongly eroded and often deformed structures, the classical criteria for proving an impact origin are not tenable. Through a combined analysis of topography, drainage, gravity, magnetic, and petrophysical data, a circular structure has been identified in northern Sweden. The structure is characterized by a circular system of faults, arc-shaped contacts between rocks, and a circular distribution of granitic intrusions. The fault zone at the edges is defined from gradients in the gravity data, from magnetic data by arc-shaped anomalies, and from topographic data by an arc-shaped relief, which is also reflected in the drainage pattern. The zone is characterized by vertical faults that also cut the granitic intrusions at the edge of the formation, and from interpretation of gravity data an uplift of high density rocks (about 2850 kg/m(exp 3)) is indicated in the central part. The age of granites and pegmatites ranges from 1.82 to 1.78 Ga. Therefore, based on age data and on paleomagnetic results of various generations of dikes that cut and are truncated by the structure, the age of the formation lies within 1.80-1.26 Ga. The rocks have not been studied petrologically to see if any traces of shock metamorphism can be found. At present, four models for the origin of the structure are possible: (1) basement doming, (2) meteorite impact, (3) large buried pluton, or (4) fault-bounded block. An impact origin, however, seems most plausible.
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| 7. |
- Romer, Rolf L., et al.
(författare)
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Svecofennian crustal deformation of the Baltic Shield and U-Pb age of late-kinematic tonalitic intrusions in the Burtrask shear zone, northern Sweden
- 1995
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Ingår i: Precambrian Research. - 0301-9268 .- 1872-7433. ; 75:1-2, s. 17-29
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Tidskriftsartikel (refereegranskat)abstract
- Post-collisional crustal deformation of the Svecofennian region involved 1) lateral escape movements along crustal-scale dominantly dextral shear zones that roughly correspond to boundaries between volcanic and sedimentary terranes, and 2) crustal thickening eventually resulting in regional migmatite-formation and granitic magmatism. U-Pb dating of titanite from skarnified limestone in the contact-metamorphic aureole of late-kinematic tonalites in the Burtrask Shear Zone, one of these major dextral shear zones in northern Sweden, yields 1825 +4-3 Ma (2σ). This age corresponds to the end of ductile deformation along the Burtrask Shear Zone, but it also coincides with important migmatite formation and granite emplacement in the southern part of the Svecofennian region.
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