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Disaggregation and reassembly of the Superior Craton on a subductionless, stagnant-lid Archaean Earth.

Bédard, Jean H. et Harris, Lyal B. (2013). Disaggregation and reassembly of the Superior Craton on a subductionless, stagnant-lid Archaean Earth. In: GAC/MAC Annual Meeting, 22-24 mai 2013, Winnipeg, Canada.

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The S&W Superior craton is considered to be a tectonic collage, with diachronous (between ~ 2.72 and ~ 2.68 Ga) collisional orogenesis propagating systematically from N to S, with an average interval of ~ 10 my between collisions. Most tectonic models assume that terrane accretion was mediated by uniformitarian plate tectonics (arcs, ridges). However, most ‘terranes’ are interpreted to have had long histories of ‘arc’ magmatism, which requires corresponding intervals of subduction and consumption of wide oceanic tracts. As a result, it becomes difficult to rationalize the uniform collision polarity and short intervals between collisions of these tiny terranes with such a model. Furthermore, the rarity or absence of Archaean ophiolites, overprinting thrust and fold belts, high-pressure rocks and paired metamorphic belts, orogenic andesites, and diagnostic source-metasomatic trace element signatures in putative arc rocks casts doubt on the very existence of Archaean subduction. Evidence from Venus implies that continental drift and Himalayan style indentation and escape tectonics can occur on telluric planets without arcs or ridges, probably as a result of basal mantle traction on deep, stiff, cold, buoyant sub-continental mantle keels. Application of such a model to the S&W Superior would involve southward drift of the Hudson’s Bay Terrane / Northern Superior Superterrane (which has the deepest keel in the Superior), with sequential accretion of these small, closely spaced ‘terranes’ to the leading edge of the drifting craton. Although most of the S&W Superior ‘terranes’ are interpreted to have been independent fragments prior to their assembly, many share a similar geological history, with older (pre-2.8Ga) basement and abundant Neo-Archaean magmatism. We propose that most of these ‘terranes’ originally belonged to an older Superior (I) craton that was partly disaggregated by the arrival and southward flow of large mantle plumes at ~ 2.75-2.7 Ga. The lithospheric mantle beneath zones of maximum extension like the Abitibi and Wabigoon were largely destroyed or attenuated by necking, and so only juvenile magmas erupted in these newly oceanized areas. NE-directed flow from the same plume system would have triggered the paroxysmal TTG magmatism of the NE-Superior, and extended its crust to generate the observed NNW fabrics.

Type de document: Document issu d'une conférence ou d'un atelier
Mots-clés libres: terre archéenne; subduction; craton; croûte cratonique supérieure
Centre: Centre Eau Terre Environnement
Date de dépôt: 19 nov. 2020 16:14
Dernière modification: 19 nov. 2020 16:14
URI: https://espace.inrs.ca/id/eprint/4034

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