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- Salminen, J., et al.
(författare)
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Paleomagnetic and geochronological studies on Paleoproterozoic diabase dykes of Karelia, East Finland-Key for testing the Superia supercraton
- 2014
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268. ; 244, s. 87-99
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Tidskriftsartikel (refereegranskat)abstract
- Paleomagnetic results are presented for two Paleoproterozoic mafic dykes in the Taivalkoski area in northern Karelia Province of the Fennoscandian shield where, based on K-Ar data, the crust has seen minimal effects of the otherwise pervasive 1.8-1.9 Ga Svecofennian orogeny. Within this study a new U-Pb baddeleyite age of 2339 +/- 18 Ma has been determined for one of the E-W trending dykes (dyke AD13). The paleomagnetic results show that a strong Svecofennian overprinting is pervasive in the area. Upon thermal or AF demagnetization four remanence directions were obtained. Most typical are the secondary Svecofennian remanence direction A (intermediate down to the NNW) and remanence direction B (intermediate down to the NNE). Component D (D = 115.4 degrees, 1=50.5 degrees, alpha(95) =2.6 degrees) yielding a virtual geomagnetic pole (VGP) D (Plat= -19.5 degrees N, Plon= 263.3 degrees, A95 = 3.1 degrees) is obtained from baked rocks for dyke WD, and based on a positive baked contact test is interpreted to represent the primary magnetization dating from about 2.4 Ga. Dyke AD13 carries only secondary A and B components, its unbaked host migmatites carry reversed A (A(R)) component, and the baked host rock carries a component D' (D = 134.5 degrees, 1= -7.3 degrees, alpha(95) = 8.8 degrees), which yields a VGP pole D' (Plat= -20.4 degrees N, Plon = 257.3 degrees, A(95) = 7.6 degrees), possibly representing magnetization at 2.3 Ga. The new paleomagnetic data from the Karelia Province compared to similar-aged paleomagnetic data from the Superior Province does not support the recently proposed Superia configuration, based upon dyke swarm trajectories. (c) 2013 Elsevier B.V. All rights reserved.
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- Buchan, K. L., et al.
(författare)
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Comparing the drift of Laurentia and baltica in the Proterozoic : the importance of key palaeomagnetic poles
- 2000
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Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 319:3, s. 167-198
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Tidskriftsartikel (refereegranskat)abstract
- Key palaeomagnetic poles are defined as those which pass basic reliability criteria and are precisely and accurately dated. They allow a more rigorous analysis of Precambrian continental drift and continental reconstructions than the traditional apparent polar wander path (APWP) approach using mostly non-key poles. Between ca. 2.45 and 2.00 Ga in the early Palaeoproterozoic, key poles define the drift of the Archaean Superior craton of Laurentia, yielding a result that is quite unlike the drift interpreted in earlier studies using the APWP method. There are no early Palaeoproterozoic key poles for the other Archaean cratons that amalgamated to form Laurentia and Baltica prior to 1.8 Ga, so that a rigorous test of early Palaeoproterozoic reconstruction models is not possible. Key poles from Laurentia between ca. 1.46 and 1.267 Ga and Baltica between 1.63 and 1.265 Ga help to define, in a preliminary fashion, the early Mesoproterozoic drift of the two shields. The key pole age match at ca. 1.265 Ga is consistent with Baltica located adjacent to eastern Greenland, and geological considerations suggest that the most reasonable fit aligns the Labradorian belt of Laurentia with the Gothian belt of Baltica. Although there is limited support from non-key poles and key poles that are not matched in age for such a fit as early as ca. 1.8 Ga, no rigorous assessment will be possible until a match in key pole ages is achieved. In the late Mesoproterozoic to Neoproterozoic, Laurentia's drift is reasonably well documented by seven key poles between 1.235 and 0.73 Ga. There are no key poles in this period from Baltica, however, so that a ≈90° clockwise rotation of Baltica relative to Laurentia between 1.265 and 1.0 Ga, widely used in the literature, cannot be confirmed.
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- Evans, David A.D., et al.
(författare)
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An expanding list of reliable paleomagnetic poles for Precambrian tectonic reconstructions
- 2021
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Ingår i: Ancient Supercontinents and the Paleogeography of Earth. - : Elsevier. ; , s. 605-639
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Bokkapitel (refereegranskat)abstract
- We present a compilation of reliable Precambrian paleomagnetic poles from three successive international workshops (in years 2009, 2014, 2017), comprising paleomagnetists specializing in Precambrian tectonic reconstructions. The working groups compiled lists of two global classes of poles, published through the end of 2017. “Grade-A” results are judged to provide essential constraints on tectonic reconstructions; “Grade-B” poles are judged to be suggestive of high-quality, but not yet demonstrated to be primary, or perhaps lacking precise geochronologic or other constraints. Our catalog documents a resurgence of high-quality data acquisition in recent years, and highlights specific cratons and time intervals that are most lacking in the data needed to reconstruct those blocks through supercontinental cycles.
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