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Wouter Bleeker, Geological Survey of Canada (Canada)
Michael A. Hamilton, University of Toronto (Canada)
Richard E. Ernst, Carleton University, and Ernst Geosciences (Canada)
Vyacheslav S. Kulikov, Geological Institute of Karelian Science Centre (Russian Federation)
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Archean cratons and their mantle roots are dispersed fragments of much larger late Archean to Paleoproterozoic landmasses, either a single late Achean supercontinent or a small number of discrete late Archean landmasses or supercratons (Bleeker, 2003).
Understanding the plate tectonic fragmentation of these late Archean supercratons is important as it will allow us: (1) to synthesize the Archean record of numerous Archean cratons within the original context of their larger ancestral supercratons; (2) to understand and synthesize the rich but equally dispersed Paleoproterozoic record of sedimentary basins, passive margins, oceanic tracts and orogens; (3) to construct a complete and accurate "fragmentation tree" of Archean crust that will help us resolve other paleogeographic questions, e.g. the configuration of Rodinia; and (4) together with more densely populated apparent polar wander paths, we can begin to define plate movements, rates, and finite translations to help constrain geodynamic models as far back as 2.6 Ga.
Among the ∼35 extant Archean cratons, at least five can be traced back to an origin within supercraton "Superia", the large ancestral landmass of which the Superior craton is a central and defining fragment. Others are: Karelia (likely including Kola in a "greater Karelia"), Hearne, and Wyoming (Bleeker & Ernst, 2006).
Here we present new constraints for the increasingly tight link between Superior and "greater Karelia", and increasing evidence for Karelia to have originated from just south of the southeastern margin of the Superior craton. Using U-Pb baddeleyite, we have dated the coarse-grained "Avdeevskiy" and "Shalskiy" gabbronorite dykes-dykes that are critical to a correct interpretation of the complex paleomagnetic data for Karelia-at ca. 2504 Ma.
As anticipated explicitly by the reconstruction of Bleeker & Ernst (2006), this is the first recognition of the ca. 2505 Ma "Mistassini event" (southeastern Superior craton) within Karelia. We thus establish that Karelia, Kola, and the southeastern portion of the Superior craton, were all proximal to each other within Superia, across the Archean-Paleoproterozoic boundary and up to Paleoproterozoic breakup, as they share at least two precisely dated magmatic events over a span of time ("the rule of multiple magmatic barcode matches"; Bleeker, IGC abstract).
Finally, our results indicate that shallow inclination poles for Karelia must be close to primary and 2.50-2.45 Ga in age, whereas another steeper inclination paleopole, although supported by a positive baked contact test, remains undated. The shallow inclination poles for Karelia allow a fit of Karelia just south of the southeastern Superior craton, as their shared geological record indicates. These findings pave the way for a final synthesis of paleomagnetic results for both cratonic fragments, from 2.6 Ga to their eventual breakup at ca. 2.0 Ga, prior to their reincorporation within supercontinent Nuna at ca. 1.8 Ga.
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