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Titre	Modern style nappe stacking in the Paleoproterozoic lower crust: An example from the snowbird tectonic zone, Canadian Shield
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Auteur	Graziani, R; Larson, K; Smit, M; Cottle, J M; Lamming, J; Piette-Lauzière, N
Source	Precambrian Research vol. 380, 106817, 2022 p. 1-21, https://doi.org/10.1016/j.precamres.2022.106817
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Année	2022
Séries alt.	Ressources naturelles Canada, Contribution externe 20220252
Éditeur	Elsevier
Document	publication en série
Lang.	anglais
DOI	https://doi.org/10.1016/j.precamres.2022.106817
Media	papier; numérique; en ligne
Formats	pdf
Province	Saskatchewan
SNRC	74O/07; 74O/08; 74P/05
Lat/Long OENS	-107.0000 -105.5000 59.5000 59.2500
Sujets	croûte continentale; zones de cisaillement; mylonites; zones tectoniques; Zone de Snowbird Tectonic ; Bouclier Canadien; géochronologie; tectonique; Précambrien
Illustrations	cartes de localisation; photomicrographies; graphiques
Diffusé	2022 08 20
Résumé	(disponible en anglais seulement) The Intra Tantato shear zone (ITSZ), which occurs within the East Athabasca mylonite triangle in the southern portion of the ~1.9 Ga Snowbird tectonic zone in northern Saskatchewan, Canada, is a low to high angle, curvi-planar, kilometer-thick mylonite zone hosted within granulite-facies gneiss that records a complex history with both thrust- and normal-sense motion. New field mapping, microstructural analysis, and quartz crystallographic preferred orientations (CPO) detail a composite history for the ITSZ that includes top-to-the-ENE thrusting of the hanging wall over the footwall that is overprinted by normal-sense top-to-the-WSW reactivation. Quartz CPOs further indicate constrictional deformation related to both events and quartz c-axis opening angles define deformation temperatures of ~750 ± 50 °C for the thrusting event and ~550 ± 50 °C for the later, normal-sense reactivation. Monazite and garnet geochronology on rocks within and around the ITSZ indicate it may have nucleated along a pre-existing 2.6-2.5 Ga sub-horizontal fabric. This appears to have occurred immediately after the ~1.920 Ga metamorphic peak of the hanging wall and during the ~1.905 Ga metamorphic peak of the footwall. Monazite ages from small matrix grains in interstitial positions in specimens that record reactivation kinematics indicate overprinting occurred at ~1.860-1.830 Ga, contemporaneous with the earliest recorded activity along the nearby Grease River Shear Zone. Overall, this tectonic evolution can be attributed to a crustal thickening process that occurred in the Athabasca mylonite triangle during the Snowbird orogeny at ~1.9 Ga and during the post-collisional exhumation processes. Moreover, these results show that the lower continental crust can actively accommodate shortening during large-scale collisional events with tectonic units piling up via nappe-stacking processes similarly to what is typically observed in the middle crust.
Sommaire	(Résumé en langage clair et simple, non publié) L'une des lacunes de connaissances sur les ceintures orogéniques est liée au comportement de la partie inférieure de la croûte continentale lors des collisions continentales. Le triangle mylonitique de l'Athabasca oriental (eAMT) est l'un des meilleurs exemples de croûte continentale inférieure. L'objectif principal de cette étude est de comprendre l'évolution structurale de cette zone avec l'analyse microstructurale et nouvelles données géochronologiques à la Intra Tantato shear zone, l'une des principales zones de mylonite associées aux processus orogéniques. Nous avons trouvé plusieurs preuves montrant que la zone de cisaillement était active à 1,9 Ga en tant que structure compressive associé à l'événement orogénique Snowbird, et qu'elle a ensuite été réactivé en tant que structure d'extension au cours des derniers stades de l'orogenèse. L'eAMT a subi des processus de compression et d'extension similaires à ceux que l'on trouve généralement dans le niveau supérieur de la croûte continentale.
GEOSCAN ID	330630