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| 2. |
- Elming, Sten-åke, et al.
(author)
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A palaeomagnetic and geochemical study of basic intrusions in northern Sweden
- 2004
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In: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 126:2, s. 243-252
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Journal article (peer-reviewed)abstract
- A palaeomagnetic and geochemical study has been performed on basic dykes in northern Sweden. The dykes and a gabbro formation were sampled in 28 sites and characteristic magnetizations could be defined in 23 of them. The dykes form a part of a swarm that trends in NE-SW to E-W. From differences in palaeomagnetic signatures and composition it is concluded that this swarm is composed of two generations of dykes, group A and B, trending in similar directions. The dykes of group A have compositions that are similar to rapakivi related dykes, while those of group B are different from most rapakivi dykes in Fennoscandia. The calculated pole positions may suggest that the group B dykes are older than those of group A and both groups intruded within the time span 1.77 Ga to 1.50 Ga. The trend of the dykes is more or less parallell to a palaeo-compressional stress field that may be expected from the collisional tectonics related to the Gothian orogeny. The intrusion of the rapakivi formations in Fennoscandia has been suggested to be related with the Gothian orogeny and the intrusion of the dykes may thus be guided by the stress field generated by the collisional tectonics.
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| 3. |
- Moakhar, Mohsen Oveisy, et al.
(author)
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A palaeomagnetic analysis of rapakivi intrusions and related dykes in the Fennoscandian Shield
- 2000
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In: Physics and chemistry of the earth. Part A. - 1464-1895 .- 1873-4642. ; 25:5, s. 489-494
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Journal article (peer-reviewed)abstract
- In the Fennoscandian Shield (Baltica) there are seven major rapakivi plutons and fifteen minor ones ranging in age from ca 1.66 to 1.50 Ga. These plutons are distributed in a broad WNW zone and if the most eastern pluton is excluded there is a westward trend of decreasing age of the intrusions. A palaeomagnetic study has been performed on 4 minor plutons (Rödö, Mårdsjö, Norsjö and Mullnäset) and associated dykes in central Sweden. The results were combined with palaeomagnetic data from other rapakivi complexes in Fennoscandia in order to test if a stationary hot spot may be the origin of these anorogenic intrusions. Plotting the pole positions of this study together with poles of other complexes, poles calculated from rapakivi rocks and related dykes in Finland are located at somewhat lower latitudes and more eastern longitudes than poles of corresponding rocks in Sweden, probably reflecting an APW related to the general age differences between the plutons. The palaeolatitudes for the Fennoscandian Shield at the time of the rapakivi intrusions are restricted to a latitudinal range between ca 16° south and 27° north and there is a weak trend of increasing palaeolatitude with decreasing age of the rocks. A trend of gradually changing palaeolatitudinal positions has also been observed for the intrusion of Proterozoic anorthosite-rapakivi plutons in the Ukranian Shield. Such differences in palaeolatitudes is not expected in case of a single stationary hot spot being the source of the rapakivi intrusions, as the rock then should carry a magnetization reflecting the same latitudinal position.
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| 4. |
- Moakhar, Mohsen Oveisy
(author)
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Rapakivi granite and basic dykes in the Fennoscandian shield : a palaeomagnetic analysis
- 1998
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Doctoral thesis (other academic/artistic)abstract
- Rapakivi rocks and basic dykes in the central part of Sweden have been subject to a palaeomagnetic study with the aim of putting the formation of these rocks into a plate tectonic context. Virtual geomagnetic poles were calculated and found to be distributed around the Jotnian Loop of the APWP of Fennoscandia. Paleolatitudes for the shield at the time of the intrusions were determied to a range from the equator to a 30 degrees North and a hot spot origin was tested as a model for the origin of the rapakivi rocks. Palaeomagnetic data from a basic dyke swarm in central Sweden suggest the dykes to be related to rapakivi intrusions, which means that this Neoproterozoic magmatism seems more widespread than was earlier suggested. From very detailed palaeomagnetic studies of basic dykes and the baked host rocks the ambient temperature of the rock at the time of intrusion of the dykes was determined at 376 degrees Celsius. A palaeothermal gradient was estimated and the depth of burial of the present erosion surface at 1.5 Ga ago was determined at 12 km.
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| 5. |
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| 6. |
- Salminen, Johanna, et al.
(author)
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Paleomagnetic studies of rapakivi complexes in the Fennoscandian shield – Implications to the origin of Proterozoic massif-type anorthosite magmatism
- 2021
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In: Precambrian Research. - : Elsevier. - 0301-9268 .- 1872-7433. ; 365
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Journal article (peer-reviewed)abstract
- Paleomagnetic studies have been performed on five rapakivi related complexes in Sweden and Finland. Poles of varying quality have been defined and the majority of the similar to 1640-1497 Ma poles are clustering on low latitudinal positions. By combining data from similar to 1500 Ma intrusions a new high-quality pole (Plat: 13 degrees N; Plon: 190 degrees E; A(95): 11 degrees, K: 14) for Baltica has been defined. Tectonic reconstructions, on the basis of the new data and previously published high-quality data, indicate that Baltica experienced stable low latitude to equatorial positions during 1640-1470 Ma, temporally coinciding with globally pronounced rapakivi-anorthosite magmatism. Our study argues against single hotspot source for similar to 1640-1620 Ma, similar to 1590-1520 Ma, and 1470-1410 Ma rapakivianorthosites, but supports a model of large-scale superswell under a stationary low-latitude position of supercontinent Nuna for the origin of rapakivi-anorthosite magmatism. However, a possibility for convergent tectonism as the origin cannot be ruled out.
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