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TitreResolving the crustal composition paradox by 3.8 billion years of slab failure magmatism and collisional recycling of continental crust
AuteurHildebrand, R S; Whalen, J B; Bowring, S A
SourceDevelopment of accretionary orogens: a celebration of the career of Cees van Staal; par Murphy, B (éd.); Lin, S (éd.); Zagorevski, A (éd.); Tectonophysics vol. 734-735, 2018 p. 69-88, https://doi.org/10.1016/j.tecto.2018.04.001
Année2018
Séries alt.Ressources naturelles Canada, Contribution externe 20170375
ÉditeurElsevier
Documentpublication en série
Lang.anglais
DOIhttps://doi.org/10.1016/j.tecto.2018.04.001
Mediapapier; en ligne; numérique
Formatspdf; html
Sujetsétudes de la croûte; evolution de la croûte; établissement de modèles; croûte continentale; tectonique de plaques; magmatisme; magmas; origine; manteau terrestre; composition en vrac; minéraux détritiques; zircon; etudes isotopiques; isotopes d'oxygène; analyses des éléments en trace; tonalites; trondhjémites; granodiorites; tectonique; pétrologie ignée et métamorphique; géochimie
Illustrationsgraphs; schematic representations; geochemical plots
ProgrammeTransitions de porphyres régionaux de l'ouest de la Cordillère, GEM2 : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
In the standard paradigm, continental crust is formed mainly by arc magmatism, but because the compositions of magma rising from the mantle are basaltic and continental crust is estimated to contain about 60% SiO2 and much less MgO than basalt, the two do not match. To resolve this paradox, most researchers argue that large amounts of magmatic fractionation produce residual cumulates at the base of the crust, which because arcs are inferred to have magmatically thickened crust, form eclogites that ultimately founder and sink into the mantle. Not only are there problems with the contrasting bulk compositions, but the standard model also fails because prior to collision most modern arcs do not have thick crust, as documented by their eruption close to sea level, and in cases of ancient arc sequences, their intercalation with marine sedimentary rocks.
Our study of Cretaceous batholiths in the North American Cordillera resolves the crustal composition paradox because we find that most are not arc-derived as commonly believed; but instead formed during the waning stages of collision and consequent slab failure. Because the batholiths typically have silica contents>60% and are derived directly from the mantle, we argue that they are the missing link in the formation of continental crust.
Slab failure magmas worldwide are compositionally similar to tonalite-trondhjemite-granodiorite suites as old as 3.8 Ga, which points to their collective formation by slab failure and long-lived plate tectonics. Our model also provides (1) an alternative solution to interpret compiled detrital zircon arrays, because episodic peaks that coincide with periods of supercontinent amalgamation are easily interpreted to represent collisions with formation of new crust by slab failure; and (2) that models of early whole-earth differentiation are more reasonable than those invoking progressive growth of continental crust.
Résumé(Résumé en langage clair et simple, non publié)
Selon le modèle depuis longtemps accepté de la formation et de l'évolution de la croûte continentale de la Terre, celle-ci s'est formée dans les arcs volcaniques et a gagné en volume au fil du temps. Toutefois, les nouveaux apports magmatiques dans les arcs sont de composition basaltique et non intermédiaire, comme le suggèrent les estimations relatives à la composition de la croûte. Cette contradiction est généralement résolue en faisant appel à la délamination des résidus mafiques denses à la base des arcs dans le manteau. Nous proposons un autre modèle selon lequel la croûte est le résultat de ruptures de plaques intermédiaires et d'un magmatisme d'arc. Ce modèle permet d'éliminer la contradiction de longue date.
GEOSCAN ID306970