Browsing by Subject "POLAR WANDER"

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  • Luoto, Toni; Salminen, Johanna; Obst, Karsten (2021)
    Baltica and Laurentia form the core of the hypothesized Mesoproterozoic supercontinent Nuna in most paleogeographical reconstructions. Long gaps still exist in the Mesoproterozoic paleomagnetic record of Baltica, and different relative configurations for Baltica and Laurentia have been presented. This study presents new paleomagnetic data obtained for mafic dykes on Bornholm (Denmark, southwest Baltica). We provide a new 1.326 +/- 0.010 Ga Bornholm Group I paleomagnetic key pole (Plat: 06 degrees N, Plon: 165 degrees E, K: 21, A95: 6 degrees) for Baltica. This pole supports the low-latitude equatorial core of Nuna at 1.33 Ga, where Kola Peninsula and Northern Norway of Baltica were facing northeastern Greenland of Laurentia. Based on statistically different magnetization directions with Group I and differences in Nb-Zr-Y systematics, we propose a separate Bornholm Group II paleomagnetic pole. This undated, poor-quality pole indicates a paleolatitude of ca. 50 degrees, possibly reflecting an age difference compared to Group I, accompanied with the continental drift. On Bornholm, the wide Listed and Kas dykes of uncertain age yield significantly different paleomagnetic results compared to the other studied dykes there. In addition, the virtual geomagnetic poles (VGPs) of these dykes are 45 degrees apart from each other. On the basis of similar Nb-Zr-Y systematics with the dykes of the 0.98-0.94 Ga Blekinge Dalarna Dolerite Group (Sweden) and overlapping paleomagnetic data with the high-quality 0.95-0.94 Ga paleomagnetic poles of Baltica, an early Neoproterozoic age for the magnetization is proposed. The relatively big discrepancy between Listed and Kas VGPs could stem from an unaveraged paleosecular variation or from a small but significant age difference during rapid plate movements.
  • Bispo-Santos, Franklin; D’Agrella-Filho, Manoel S.; Pesonen, Lauri J.; Salminen, Johanna M.; Reis, Nelson J.; Silva, Julia Massucato (2020)
    In recent years, there has been a significant increase in the paleomagnetic data of the Amazonian Craton, with important geodynamic and paleogeographic implications for the Paleo-Mesoproterozoic Columbia supercontinent (a.k.a., Nuna, Hudsoland). Despite recent increase of paleomagnetic data for several other cratons in Columbia, its longevity and the geodynamic processes that resulted in its formation are not well known. A paleomagnetic study was performed on rocks from the similar to 1535 Ma AMG (Anorthosite-Mangerite-Rapakivi Granite) Mucajai Complex located in the Roraima State (Brazil), in the northern portion of the Amazonian Craton, the Guiana Shield. Thermal and AF treatments revealed northwestern/southeastern directions with upward/downward inclinations for samples from twelve sites. This characteristic remanent magnetization is mainly carried by Ti-poor magnetite and in a lesser amount by hematite. Site mean directions were combined with previous results obtained for three other sites from the Mucajai Complex, producing the dual polarity mean direction: Dm = 132.2 degrees; Im = 35.4 degrees (N = 15; alpha(95) = 12.7 degrees; k = 10.0) and a paleomagnetic pole located at 0.1 degrees E, 38.2 degrees S (A(95) = 12.6 degrees; K = 10.2). The Mucajai pole favours the SAMBA (South AMerica-BAltica) link in a configuration formed by Amazonia and Baltica in Columbia. Also, there is geological and paleomagnetic evidence that the juxtaposition of Baltica and Laurentia at 1.76-1.26 Ga forms the core of Columbia. The present paleomagnetic data predict a long life 1.78-1.43 Ga SAMBA connection forming part of the core of the supercontinent. (c) 2019 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
  • Wang, Chong; Mitchell, Ross N.; Murphy, J. Brendan; Peng, Peng; Spencer, Christopher J. (2021)
    Supercontinent Pangea was preceded by the formation of Gondwana, a ?megacontinent? about half the size of Pangea. There is much debate, however, over what role the assembly of the precursor megacontinent played in the Pangean supercontinent cycle. Here we demonstrate that the past three cycles of supercontinent amalgamation were each preceded by ?200 m.y. by the assembly of a megacontinent akin to Gondwana, and that the building of a megacontinent is a geodynamically important precursor to supercontinent amalgamation. The recent assembly of Eurasia is considered as a fourth megacontinent associated with future supercontinent Amasia. We use constraints from seismology of the deep mantle for Eurasia and paleogeography for Gondwana to develop a geodynamic model for megacontinent assembly and subsequent supercontinent amalgamation. As a supercontinent breaks up, a megacontinent assembles along the subduction girdle that encircled it, at a specific location where the downwelling is most intense. The megacontinent then migrates along the girdle where it collides with other continents to form a supercontinent. The geometry of this model is consistent with the kinematic transitions from Rodinia to Gondwana to Pangea.