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TitreInfluence of deformation and fluids on Ar retention in white mica: dating the Dover Fault, Newfoundland Appalachians
AuteurKellett, D A; Warren, C; Larson, K P; Zwingmann, H; van Staal, C R; Rogers, N
SourceLithos vol. 254-255, 2016 p. 1-17, https://doi.org/10.1016/j.lithos.2016.03.003
Année2016
Séries alt.Commission géologique du Canada, Contributions aux publications extérieures 20150445
Séries alt.Secteur des sciences de la Terre, Contribution externe 20150445
ÉditeurElsevier
Documentpublication en série
Lang.anglais
DOIhttps://doi.org/10.1016/j.lithos.2016.03.003
Mediapapier; en ligne; numérique
Formatspdf
ProvinceNouveau-Brunswick; Terre-Neuve-et-Labrador; Québec; Île-du-Prince-Édouard
SNRC1M/03; 1M/04; 1M/05; 1M/06; 1M/07; 1M/10; 1M/11; 1M/12; 1M/13; 1M/14; 1M/15; 1M/16; 2C/04; 2C/05; 2C/11; 2C/12; 2C/13; 2C/14; 2D/01; 2D/02; 2D/03; 2D/04; 2D/05; 2D/06; 2D/07; 2D/08; 2D/09; 2D/10; 2D/11; 2D/15; 2D/16; 2E/01; 2E/02; 2E/08; 2E/09; 2F/02; 2F/03; 2F/04; 2F/05; 2F/06; 2F/12; 11P/08; 11P/09; 11P/16
Lat/Long OENS -56.4167 -52.8750 49.6250 47.0000
Sujetsinterprétations tectoniques; antécédents géologiques; terrains; évolution tectonique; antecedents thermiques; déformation; temperature; mise en place; datation radiométrique; datation argon-argon; datation au uranium-plomb; mica; cristallisation; recristallisation; caractéristiques structurales; failles, décrochement; zones de cisaillement; fluage; roches ignées; roches intrusives; granites; illite; filons rocheux; Orogène Appalachien; Avalonie; Ganderie; Faille de Dover ; Faille d'Hermitage Bay ; Granite d'Ackley ; Orogenèse Acadienne; Orogenèse de Salinic ; Granite d'Harbour Breton ; géologie structurale; pétrologie ignée et métamorphique; géochronologie; Phanérozoïque; Paléozoïque; Carbonifère; Mississippien; Dévonien; Silurien
Illustrationsgeological sketch maps; photographs; schematic cross-sections; tables; photomicrographs; equal-area stereonet projections; Concordia diagrams; plots; spectra
ProgrammeÉtude des gîtes porphyriques, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
White mica 40Ar/39Ar analyses may provide useful constraints on the timing of tectonic processes, but complex geological and thermal histories can perturb Ar systematics in a variety of ways. Ductile shear zones represent excellent case studies for exploring the link(s) between dynamic re-/neo-crystallization of white mica and coeval enhanced fluid flow, and their effect on 40Ar/39Ar dates. White mica 40Ar/39Ar dates were collected from compositionally similar granites that record different episodes of deformation with proximity to the Dover Fault, a terrane-bounding strike-slip shear zone in the Appalachian orogen, Newfoundland, Canada. 40Ar/39Ar data were collected in situ by laser ablation and by step heating single crystals. Results were compared to each
other and against complementary U-Pb zircon and monazite, and K-Ar fault gouge analysis. Although step-heat 40Ar/39Ar is a widely applied method in orogenic settings, this dataset shows that relatively flat step-heat 40Ar/39Ar spectra are in contradiction with wide spreads in in-situ 40Ar/39Ar dates from the same samples, and that plateau dates in some cases yielded mixed dates of equivocal geological significance. This result indicates that the step-wise release of Ar from white mica likely homogenizes and obscures spatially-controlled Ar isotope reservoirs in white mica from sheared rocks. In contrast, in situ laser ablation 40Ar/39Ar analysis preserves the spatial resolution of 40Ar reservoirs that have been variably reset by deformation and fluid interaction. This study therefore suggests that laser ablation is the best method for dating the timing of deformation recorded by white mica. Final interpretation of results should be guided by microstructural analysis, estimation of deformation temperature, chemical characterization of white mica, and complementary chronometers. Overall the dataset shows that granitic protoliths were emplaced between 430 and 422 Ma (U-Pb zircon). High strain deformation along the Wing Pond Shear Zone occurred between ca. 422-405 Ma (U-Pb monazite and 40Ar/39Ar). Subsequent patchy Ar loss in white mica occurred locally during low T shear (b400 C), and via post-deformation fluid interactions. Low-temperature reactivation of the Dover Fault, a narrow segment of the Wing Pond shear zone, occurred at ca. 385 Ma (40Ar/39Ar). K-Ar dating of authigenic illite in fault gouge from the broadly co-linear brittle Hermitage Bay Fault indicates that slip along the terrane boundary persisted until at least the Mississippian.
Résumé(Résumé en langage clair et simple, non publié)
Le « mica blanc » est un minéral qui contient du potassium. La désintégration naturelle du potassium en gaz argon dans le mica blanc peut constituer une méthode de datation des événements de l'histoire géologique. Dans le présent document, nous utilisons deux techniques différentes pour déterminer l'âge du mica blanc qui a été déformé dans une importante zone de cisaillement à Terre-Neuve. Nous soutenons que, dans différents échantillons, le gaz argon contenu dans le mica blanc a été libéré de façon variable par la diffusion thermique, les processus de déformation et l'infiltration de fluides. Les âges obtenus sont utilisés pour reconstituer la chronologie des événements majeurs de la formation de la chaîne des Appalaches, y compris l'accrétion des blocs crustaux de la Ganderia, de l'Avalonia et de Meguma à la marge occidentale du continent nord-américain.
GEOSCAN ID297659