| 1. |
- Evans, David A.D., et al.
(author)
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An expanding list of reliable paleomagnetic poles for Precambrian tectonic reconstructions
- 2021
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In: Ancient Supercontinents and the Paleogeography of Earth. - : Elsevier. ; , s. 605-639
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Book chapter (peer-reviewed)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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| 2. |
- Nysaether, E, et al.
(author)
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Ordovician palaeogeography with new palaeomagnetic data from the Montagne Noire (Southern France)
- 2002
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In: Earth and Planetary Science Letters. - 1385-013X. ; 203:1, s. 329-341
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Journal article (peer-reviewed)abstract
- A joint palaeomagnetic and Ar-40/Ar-39 study has been performed on two olistolithic blocks from the Cabrieres Wildflysch in the Montagne Noire region of the Massif Central in France. There, andesitic volcanic and volcaniclastic rocks of Llanvirn-Early Caradoc age (ca 470-458 Ma) occur. Despite extensive secondary alteration, destruction of the dominant magnetic mineral phase and Ar-40/Ar-39 whole rock experiments that demonstrate that the volcanic rocks suffered significant argon loss, a positive fold test and the presence of dual polarities suggest that a primary, Ordovician magnetisation has mostly survived. This is one of the few documented cases where the argon system was substantially reset whilst a subordinate set of small, relatively unaltered magnetite grains, probably hosted in silicates, still carry the original, in this case Ordovician, remanence. The new data show that the Montagne Noire region was located at high southerly latitudes (68degrees (+19)/(-15)) during the Mid-Ordovician. This latitude represents the location for NW Gondwana of which the Massif Central was a part. Palaeomagnetic data from all the Central European massifs and terranes demonstrate a close link to the Gondwana Margin during the Lower and Middle Ordovician.
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| 3. |
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| 4. |
- Rehnström, Emma, et al.
(author)
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Evidence of a Late Precambrian (637 Ma) deformational event in the Caledonides of northern Sweden
- 2002
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In: Journal of Geology. - 0022-1376. ; 110:5, s. 591-601
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Journal article (peer-reviewed)abstract
- The Caledonian nappes in Scandinavia record two main phases of early Paleozoic metamorphism, but their pre-Caledonian tectonothermal history and paleogeographic position are largely unknown. Here we present a U-Pb age of 637+/-3 Ma for metamorphic titanite in the 1776+/-4 Ma (zircon age) Skarja granitic gneiss in northern Sweden. The titanite age is interpreted to represent a Neoproterozoic tectonometamorphic overprint. Geochronologic and paleogeographic considerations suggest that the gneiss was located at the outermost margin of pre-Caledonian (northwest) Baltica and was affected by Neoproterozoic tectonic activity related to terrane accretion, the Baikalian (or Timanian) orogeny, coincident with Cadomian terrane accretion along the Gondwanan margin of northern South America and northwest Africa.
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| 5. |
- Torsvik, Trond H, et al.
(author)
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The Taimyr fold belt, Arctic Siberia: timing of prefold remagnetisation and regional tectonics
- 2002
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In: Tectonophysics. - 0040-1951. ; 352:3-4, s. 335-348
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Journal article (peer-reviewed)abstract
- Late Precambrian and Palaeozoic platform sediments from the Central-South Taimyr Peninsula (Arctic Siberia) are all remagnetised. The remagnetisation is prefold and is related to thermal remagnetisation caused by Taimyr Trap magmatism. The remagnetisation age is estimated to 220-230 Ma and, hence, is considerably younger than the ca. 251 Ma age for the main body of Siberian Trap flood basalts. The folding that affected the Taimyr region platform sediments also included the Taimyr "Traps," hence, relegating Taimyr deformation to post-Mid Triassic time, and most probably, to a Late Triassic age. This shows that whilst thrusting terminated in the Urals during the Permian, crustal shortening continued in Taimyr, Novaya-Zemlya and the South Barents Sea, well into the Mesozoic. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 6. |
- Torsvik, Trond H, et al.
(author)
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The Tomquist Sea and Baltica-Avalonia docking
- 2003
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In: Tectonophysics. - 0040-1951. ; 362:1-4, s. 67-82
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Journal article (peer-reviewed)abstract
- Early Ordovician (Late Arenig) limestones from the SW margin of Baltica (Scania-Bomholm) have multicomponent magnetic signatures, but high unblocking components predating folding, and the corresponding palaeomagnetic pole (latitude = 19degreesN, longitude = 051degreesE) compares well with Arenig reference poles from Baltica. Collectively, the Arenig poles demonstrate a midsoutherly latitudinal position for Baltica, then separated from Avalonia by the Tomquist Sea. Tornquist Sea closure and the Baltica-Avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for Avalonia and Baltica during the Mid-Late Ordovician. By the Caradoc, Avalonia had drifted to palaeolatitudes compatible with those of SW Baltica, and subduction beneath Eastern Avalonia was taking place. We propose that explosive vents associated with this subduction and related to Andean-type magmatism in Avalonia were the source for the gigantic Mid-Caradoc (c. 455 Ma) ash fall in Baltica (i.e. the Kinnekulle bentonite). Avalonia was located south of the subtropical high during most of the Ordovician, and this would have provided an optimum palaeoposition to supply Baltica with large ash falls governed by westerly winds. In Scama, we observe a persistent palaeomagnetic overprint of Late Ordovician (Ashgill) age (pole: latitude-4degreesS, longitude= 012degreesE). The remagnetisation was probably spurred by tectonic-derived fluids since burial alone is inadequate to explain this remagnetisation event. This is the first record of a Late Ordovician event in Scania, but it is comparable with the Shelveian event in Avalonia, low-grade metamorphism in the North Sea basement of NE Germany (440-450 Ma), and sheds new light on the Baltica-Avalonia docking. (C) 2002 Elsevier Science B.V. All rights reserved.
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