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TitleAn orogenic wedge model for diachronous deformation, metamorphism, and exhumation in the hinterland of the northern Canadian Cordillera
AuthorStaples, R D; Gibson, H D; Colpron, M; Ryan, J J
SourceLithosphere vol. 8, no. 2, 2016 p. 165-184, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20140467
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
Subjectsstructural geology; general geology; amphibolites; burial history; metamorphism; crustal studies; Cretaceous; Jurassic; Permian
ProgramGEM2: Geo-mapping for Energy and Minerals Western Cordillera, Redefinition of crustal blocks
Released2016 01 25
AbstractDevelopment of amphibolite facies transposition fabrics found throughout the northern Canadian Cordilleran hinterland occurred diachronously in Permo-Triassic, Early Jurassic, Middle to Late Jurassic and Early to mid-Cetaceous time. Rocks tectonized in the Permo-Triassic and Early Jurassic were exhumed in the Early Jurassic, while rocks immediately to the northeast (toward the foreland) were not buried and heated until the Middle Jurassic to mid-Cretaceous. Early Jurassic to mid-Cretaceous overthrusting (or emplacement) of Yukon-Tanana terrane on the North American continental margin, together with the imbrication of parautochthonous rocks, formed a foreland-propagating orogenic wedge. Cooler rocks in front of the wedge were progressively buried and metamorphosed to amphibolite facies from the Jurassic to Early Cretaceous as they were underthrust into a ductile shear zone near the base of the overriding wedge. Rocks previously incorporated into this zone were displaced upward and exhumed through the combined effects of renewed underplating at depth and compensating extensional and erosional denudation above to maintain a critically tapered wedge. The mid-Cretaceous metamorphic hinterland changed from orogen-perpendicular wedge dynamics in operation since the Early Jurassic to orogen-parallel extension. Rocks incorporated into the mid-crustal shear zone in the Middle Jurassic to Early Cretaceous were exhumed in the mid-Cretaceous along southeast-directed (orogen-parallel) extensional faults from beneath a supracrustal 'lid' tectonized in the Permo-Triassic and Early Jurassic. Like the Himalayan orogen and eastern Alps, orogen-parallel extension developed in an orthogonal plate convergent setting, simultaneous with, and bounded by, orogen-parallel strike-slip faulting that facilitated northwestward lateral extrusion of rocks normal to the direction of convergence.
Summary(Plain Language Summary, not published)
By applying sophisticated dating techniques at the Geological Survey of Canada geochronology lab, on well chosen rocks samples from the west central Yukon and Finlayson Lake area of southeast Yukon, the authors were able to reveal previously unrecognized Middle Jurassic to middle Cretaceous ancient mountain building events in the Yukon, that helps refine the ancient tectonic evolution of the Canadian Cordilleran mountain chain. It creates a new tectonic model that deformation and metamorphism migrated toward the foreland and downwards in the Middle Jurassic to middle Cretaceous, in part contemporaneous with and analogous to that in the southeastern Canadian Cordillera. Collapse of the thickened mountain belt happened in the middle Cretaceous by lateral fault movements.

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