Subduction beneath Laurentia modified the eastern North American cratonic edge: Evidence from P wave and S wave tomography

Boyce, A.; Bastow, I. D.; Darbyshire, F. A.; Ellwood, A. G.; Gilligan, A.; Levin, V. et Menke, W. (2016). « Subduction beneath Laurentia modified the eastern North American cratonic edge: Evidence from P wave and S wave tomography ». Journal of Geophysical Research: Solid Earth, 121(7), pp. 5013-5030.

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Résumé

The cratonic cores of the continents are remarkably stable and long-lived features. Their ability to resist destructive tectonic processes is associated with their thick (∼250 km), cold, chemically depleted, buoyant lithospheric keels that isolate the cratons from the convecting mantle. The formation mechanism and tectonic stability of cratonic keels remains under debate. To address this issue, we use P wave and S wave relative arrival-time tomography to constrain upper mantle structure beneath southeast Canada and the northeast USA, a region spanning three quarters of Earth's geological history. Our models show three distinct, broad zones: Seismic wave speeds increase systematically from the Phanerozoic coastal domains, through the Proterozoic Grenville Province, and to the Archean Superior craton in central Québec. We also recover the NW-SE trending track of the Great Meteor hot spot that crosscuts the major tectonic domains. The decrease in seismic wave speed from Archean to Proterozoic domains across the Grenville Front is consistent with predictions from models of two-stage keel formation, supporting the idea that keel growth may not have been restricted to Archean times. However, while crustal structure studies suggest that Archean Superior material underlies Grenvillian age rocks up to ∼300 km SE of the Grenville Front, our tomographic models show a near-vertical boundary in mantle wave speed directly beneath the Grenville Front. We interpret this as evidence for subduction-driven metasomatic enrichment of the Laurentian cratonic margin, prior to keel stabilization. Variable chemical depletion levels across Archean-Proterozoic boundaries worldwide may thus be better explained by metasomatic enrichment than inherently less depleted Proterozoic composition at formation.

Type:	Article de revue scientifique
Informations complémentaires:	©2016. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Mots-clés ou Sujets:	Body wave Tomography, Cratonic Margins, Grenville Orogeny, SE Canada
Unité d'appartenance:	Centres institutionnels > Centre de recherche en géochimie et géodynamique (GEOTOP) Faculté des sciences > Département des sciences de la Terre et de l'atmosphère
Déposé par:	Marie Larocque
Date de dépôt:	27 sept. 2016 15:12
Dernière modification:	01 nov. 2016 13:43
Adresse URL :	http://archipel.uqam.ca/id/eprint/8918

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