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TitreLate Paleozoic assembly of the Alexander-Wrangellia-Peninsular composite terrane, Canadian and Alaskan Cordillera
AuteurBeranek, L P; van Staal, C R; McClelland, W C; Joyce, N; Israel, S
SourceGeological Society of America Bulletin vol. 126, no. 11-12, 2014., https://doi.org/10.1130/31066.1
Année2014
Séries alt.Secteur des sciences de la Terre, Contribution externe 20140045
ÉditeurGeological Society of America
Documentpublication en série
Lang.anglais
DOIhttps://doi.org/10.1130/31066.1
Mediapapier; en ligne; numérique
Formatspdf
ProvinceYukon
Sujetsterrains; analyses spectrométriques; datations au uranium-plomb; géochimie du niobium; géochimie du strontium; antécédents tectoniques; géologie structurale; géologie générale; géochronologie; Permien; Paléozoïque
ProgrammeGisements polymétalliques - nord-ouest de la Cordillère canadienne (Yukon et Colombie-Britannique), GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Late Paleozoic assembly of the Alexander-Wrangellia-Peninsular (AWP) composite terrane or Insular superterrane is recorded by two phases of regional deformation, metamorphism, and magmatism within basement complexes of the Alexander (Craig and Admiralty subterranes), Wrangellia, and Peninsular terranes in the Canadian and Alaskan Cordillera. A combination of new ion-microprobe (SIMS) and chemical abrasion-isotope dilution (CA-ID-TIMS) zircon U-Pb geochronology, whole-rock radiogenic isotope (Sr, Nd) and major and trace element geochemistry, and field studies were conducted to identify the precise timing and significance of late Paleozoic tectonism in the Saint Elias Mountains region of southwestern Yukon and eastern Alaska. Middle to Late Pennsylvanian (301-307 Ma) igneous rocks herein assigned to the Barnard Glacier suite were preferentially emplaced along the Craig subterrane-Wrangellia boundary and mainly comprise syenite-monzonite-granite plutons that intrude Paleozoic country rocks with evidence of Pennsylvanian or older (D1) deformation. We propose that Barnard Glacier suite magmatism was produced by a slab breakoff event after the consumption of a narrow ocean basin and Early Pennsylvanian collision between the Wrangellia-Peninsular arc and Craig subterrane passive margin. Early Permian (284-291 Ma) igneous rocks herein assigned to the Donjek Glacier suite comprise the vestiges of an extensive magmatic system that spanned the length of the Craig subterrane from southwestern Yukon to southeastern Alaska. The available data are consistent with Donjek Glacier suite magmatism to represent a short-lived, Early Permian arc system that initiated along the outboard margin of Craig subterrane-Wrangellia-Peninsular block after Pennsylvanian arc-collision and slab breakoff. At two field localities in southwestern Yukon, late Early Permian (ca. 285 Ma) dikes and apophyses of the Donjek Glacier suite that intrude Paleozoic country rocks with D1 structural fabrics also display evidence for ongoing regional deformation and metamorphism. Field evidence for ca. 285 Ma tectonism in the Saint Elias Mountains implies direct connections with Permian deformation and metamorphism in the Admiralty subterrane, a microcontinent in the Admiralty Island region of southeastern Alaska that developed separately from the Craig subterrane during late Neoproterozoic to late Paleozoic time. We propose that this tectonism was related to the entry of the Admiralty subterrane passive margin into the Early Permian subduction zone, which resulted in collision and final amalgamation of the AWP composite terrane. Our Early Permian tectonic scenario requires the present-day configuration of the Alexander terrane (Craig + Admiralty subterranes) to have never existed as a separate lithospheric fragment. Biogeographic and other geological data suggest that the two-part assembly of the AWP composite terrane took place along a convergent margin system to the north of the so-called Cordilleran pericratonic arc terranes (Yukon-Tanana, Quesnellia, Stikine and others), in between the paleo-Pacific and paleo-Arctic Ocean realms, to the northwest of the supercontinent Pangea. The assembly of the AWP composite terrane might have been the driving force behind the Early to Middle Permian subduction polarity flip recognized in the Cordilleran pericratonic realm, which evenutally led to the closure of a marginal ocean basin and Late Permian arc-continent collision along the western margin of North America.
Résumé(Résumé en langage clair et simple, non publié)
La géochronologie des unités de roches intrusives indique quand et comment divers terranes du superterrane insulaire se sont assemblés pour former la partie ouest de la Cordillère canadienne au Yukon et dans le nord de la Colombie-Britannique. Pendant la période s'échelonnant du Crétacé moyen au Paléozoïque tardif, les terranes se sont déplacés par translation depuis l'océan paléo-Arctique, où ils se sont formés, à l'océan paléo-Pacifique. Les terranes insulaires renferment de nombreux gisements de minéraux dont on peut maintenant lier la formation directement à leur évolution tectonique.
GEOSCAN ID293948