Key paleomagnetic poles and their use in Proterozoic continent and supercontinent reconstructions: A review

摘要

Key paleomagnetic poles are poles that are well defined and precisely dated. The rock unit from which the pole is derived must have a precise (usually U-Pb) age and the pole itself must be demonstrated primary with a rigorous field test. The use of key poles is essential in defining reliable apparent polar wander paths (APWPs) and establishing continental reconstructions. Many hundreds of Proterozoic paleopoles have been published from around the globe, but only ～45 are from large craton interiors and pass the key pole criteria. Most key poles are from mafic dykes and sills in the Superior craton (pre-1.83Ga) or Laurentia (post-1.80 Ga) or Baltica. As a result, with occasional exceptions, it is difficult to define or compare reliable APWP segments in order to test Proterozoic continental reconstructions. However, there are now sufficient age matches or approximate age matches for pairs of key poles from a number of cratons to help constrain their relative locations. In this analysis, Proterozoic key poles are identified and their use in constructing APWPs and testing continent and supercontinent reconstructions is discussed. This key pole database establishes a well constrained Superior craton-Laurentia APWP for much of the Proterozoic that can be used as a reference track against which a growing number of individual key poles from other cratons can be compared. There is now a robust Baltica-Laurentia reconstruction for ～330 m.y. between 1.59 and 1.26 Ga using this approach and potentially for ～570 m.y. between 1.83 and 1.26 Ga if additional key and non-key poles from well-dated units are considered. Key pole comparisons for several other cratons yield preliminary constraints on the relative movement of cratons (e.g., Slave and Superior cratons in the Paleoproterozoic) or on specific elements of continental reconstructions (e.g., Amazonia and Baltica in the Mesoproterozoic, South China craton and Australia in the Neoproterozoic, or Baltica and Laurentia also in the Neoproterozoic).