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| 2. |
- 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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| 3. |
- Buchan, Kenneth L., et al.
(författare)
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Rodinia : the evidence from integrated palaeomagnetism and U-Pb geochronology
- 2001
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Ingår i: Precambrian Research. - 0301-9268 .- 1872-7433. ; 110:1-4, s. 9-32
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Tidskriftsartikel (refereegranskat)abstract
- Of many hundreds of well-defined palaeomagnetic poles that have been reported from cratons around the world in the 1700-500 Ma period, only a few are precisely dated. However, such ‘key' palaeopoles are a prerequisite for establishing rigorous palaeomagnetic reconstructions in order to chart the assembly, drift and breakup of the postulated late Precambrian supercontinent of Rodinia. Most key palaeopoles are derived from mafic dykes and sills that have been dated by U-Pb techniques. Most are from Laurentia, the largest and best studied of the continental fragments that are thought to have comprised Rodinia. Thirteen key Laurentia palaeopoles form an incomplete reference set that can be used for comparison with key palaeopoles from other cratons as they become available. Currently, there are four key palaeopoles for Baltica between 1700 and 500 Ma, although only one allows a direct comparison with a similar aged pole from Laurentia. The 1265 Ma match between Baltica and Laurentia is consistent with reconstructions in which Baltica is adjacent to present-day east Greenland, with the ca. 1700-1500 Ma Gothian and Labradorian belts aligned. Few key palaeopoles are yet available from other cratons. However, recent U-Pb dating of dykes, sills, or volcanic rocks in the Siberian, Australian and Kalahari cratons and in Coats Land of Antarctica constrains the ages of individual palaeopoles from each of these areas. Most of these are not key palaeopoles because they have not been conclusively demonstrated to be primary, or local tectonic rotations have not been ruled out. Nevertheless, they are useful in testing Rodinia reconstructions. In this paper, a U-Pb baddeleyite age is reported from the late Gardar magmatic rocks of southwest Greenland. Along with the previously published palaeopole for this unit, this age helps constrain the Mesoproterozoic location of southwest Greenland relative to North America.
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| 4. |
- Bylund, G., et al.
(författare)
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Från Söderhavet till Arktis
- 2000
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Ingår i: Har du tid?. - Stockholm : Naturvetenskapliga forskningsrådet (NFR). - 9154603579 ; , s. 61-74
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Bokkapitel (populärvet., debatt m.m.)
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| 7. |
- D'Agrella-Filho, M.S., et al.
(författare)
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Paleomagnetic evidence for oblique collision between Amazonia and Laurentia at about 1.1 Ga
- 2004
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Ingår i: International Geological Congress, Abstracts. ; , s. 1089-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The connection between Amazonia and Laurentia at late Meso- proterozoic times through the Grenville/Sunsas-Aguapei collisional belts is a key feature of Rodinia paleogeography.However, at least three different geometries are proposed for such connection, mainly due to the paucity of paleomagnetic data for Amazonia.Connections along Greenland and Labrador were initially proposed based on the fit of geological provinces and scarse virtual geomagnetic poles.More recently, a connection through the Llano belt in Texas was proposed based on a single well dated 1.2 Ga paleopole obtained in mafic rocks from the Nova Floresta Formation. We present a series of poles obtained on sedimentary rocks of the Aguapei Group (western Matto Grosso State-Amazonian Craton) and intrusive mafic rocks, whose evolution is related to the Meso-Neoproterozoic Aguapei-Sunsas orogeny (1.3-0.9 Ga).Together with the 1.2 Ga Nova Floresta pole, they define a straight apparent polar wander path which matches the Laurentia APWP by 1.1 Ga for a connection along the (present day) Labrador region. The pole's trajectories imply a high degree of obliquity for such a collision in agreement with tectonic models put forward for the southwestern margin of Amazonia, the southeastern margin of Laurentia and the southwestern margin of Baltica.
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| 8. |
- Elming, Sten-åke, et al.
(författare)
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A palaeomagnetic and geochemical study of basic intrusions in northern Sweden
- 2004
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 126:2, s. 243-252
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Elming, Sten-åke, et al.
(författare)
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A palaeomagnetic study and age determinations of Tertiary rocks in Nicaragua, Central America
- 2001
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Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 147:2, s. 294-309
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Tidskriftsartikel (refereegranskat)abstract
- Palaeomagnetic, K-Ar and Ar40/Ar39 measurements have been made to elucidate Nicaragua's plate tectonic history. These show that the Nicaraguan Highland rotated 90° counterclockwise between 30 and 18 Myr ago, but the Pacific Coastal Plain has not rotated.A lack of data has prevented a direct comparison with the tectonic history of adjacent areas, in particular, the Chortis Block, which is the part of the Caribbean Plate that is geologically most closely related to the Nicaraguan Highland. However, our data suggest that the Caribbean Plate in this part of Central America was not consolidated until c. 15 Ma.
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