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TitreVertical vs horizontal Archean tectonics: a study of the North Caribou Greenstone Belt, NW Ontario
AuteurSchneider, D A; Van Lankvelt, A; Kalbfleisch, T; Duff, J; Hattori, K
SourceAssociation géologique du Canada-Association minéralogique du Canada, Réunion annuelle, Programme et résumés vol. 35, 2012 p. 124
LiensOnline - En ligne
Séries alt.Secteur des sciences de la Terre, Contribution externe 20150088
ÉditeurAssociation géologique du Canada
RéunionThe Geological Association of Canada (GAC) and the Mineralogical Association of Canada (MAC)Joint Annual Meeting; St. John's, NL; CA; mai 27-29, 2012
Documentpublication en série
Mediapapier; en ligne; numérique
SNRC52O; 53B
Lat/Long OENS-92.0000 -90.0000 53.0000 51.0000
SujetsArchéen; subduction; établissement de modèles; datations au uranium-plomb; datations au zircon; analyses structurales; datations argon-argon; monazite; zones de cisaillement; tectonique; géochronologie; géologie structurale; Précambrien
ProgrammeÉtude des gîtes de sulfures massifs volcaniques, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
The North Caribou Greenstone Belt (NCGB) is in the centre of the North Caribou Terrane (NCT), at the nucleus of the western Superior Province (WSP). A persistent problem plaguing the Archean field geologist is that regionally penetrative planar structures measured at the surface are typically subvertical; whereas, with seismic studies, only structures at shallow angles can be imaged. Our mapping along the NCGB confirms a dominant planar vertical fabric (foliation, upright fold axes), with gentle to moderate plunging lineations (fold axes, intersection lineations), a notable lack of strong L-tectonites, and occasional steep lineations in iron formations of the greenstone belt. This has implicated a primary horizontal tectonic regime responsible for the assembly and architecture of the NCT. Built on a >3.0 Ga basement, a dominant 2.87-2.85 Ga back arc-type volcano-plutonic tonalite sequence was formed near or on a thinned NCT margin. New LA-ICPMS in situ zircon U-Pb ages from St ± Al2SiO5 ± Btbearing metasediments are similarly 2.86 Ga, suggesting metamorphism synchronous with, if not a consequence of, elevated temperatures due to magmatism. This phase of crustal growth maybe the only vertical tectonic aspect in the NCT evolution as plutons and batholiths were assembled. Peak amalgamation within the WSP occurred c. 2.75-2.72 Ga in a series of discrete docking events with the NCT above a doubly-vergent subductiontype setting. Preservation of the pervasive 2.87-2.85 Ga ages suggest the NCT remained relatively cold and rigid during peak accretion and new 2.73 Ga U-Pb zircon rim and titanite ages record a metamorphic event coeval with volumetrically small re-melting episodes of more evolved granodioritic to granitic compositions. Continued accretion along the southern margin resulted in localized deformation and hydrothermal flow within the NCGB as inferred by c. 2.66-2.63 Ga Sm-Nd garnet and Pb-Pb accessory mineral ages within zones of intense strain. Ar-Ar ages of biotite and amphibole from central NCGB and new total-Pb in situ monazite ages from the North Caribou-Totogan Shear Zone yield c. 2.45 Ga ages, which likely correspond to an upper greenschist facies (400-500°C) tectonothermal pulse and structural reactivation nearly 200 m.y. after the latest stage of tectonism. Lithoprobe workers proposed the flat-lying geometry and inferred amphibolite composition of the imaged mafic slab beneath the WSP is consistent with Archean subduction models and can be used to explain the predominance of TTG suites in the Archean. The growing dataset of geochronology from the WSP is resolving a 400 m.y. long Andean- / Cordilleran-type margin, and the deformation pattern is consistent with that of horizontal tectonics.