Tectonic evolution of the Selkirk fan, southeastern Canadian Cordillera: A composite Middle Jurassic–Cretaceous orogenic structure

Abstract

The eastward transition from penetrative ductile deformation, metamorphism, and plutonism in the hinterland of the southern Canadian Cordillera to the “thin‐skinned” deformation of the foreland represents a significant change in tectonic style and process. The transition is also marked by a zone of structural divergence across which SW vergent hinterland structures pass into NE vergent foreland structures. The Selkirk fan within the Selkirk Mountains of the southern Canadian Cordillera is considered a type locality for this zone. This structure trends SE–NW for more than 120 km in greenschist to upper amphibolite facies rocks that have at least three generations of superposed deformation. The kinematic development of the Selkirk fan has been controversial, but its age generally has been inferred to be Middle to Late Jurassic. However, new U‐Th‐Pb dates obtained by ID‐TIMS and SHRIMP indicate a more protracted history. The data demonstrate that a protofan developed in the Middle Jurassic (172–167 Ma) and that the west flank of the fan was exhumed to upper crustal levels at this time. Conversely, the eastern flank was progressively buried to >25 km depth and pervasively overprinted by Cretaceous deformation (104–84 Ma) and Cretaceous‐Paleocene metamorphism (144–56 Ma). A new tectonic model is proposed to reconcile the composite nature and protracted development (>100 Ma) of the Selkirk fan within an orogenic system that evolved in response to periods of terrane accretion on the western margin of the North American craton.

Late Jurassic flare‐up of the Coast Mountains arc system, NW Canada, and dynamic linkages across the northern Cordilleran orogen

“…Southwest directed thrusting within Stikinia and Cache Creek terrane (Figure ) is considered to indicate Middle Jurassic linkages with southwest vergent folding and thrusting in the parautochthonous Omineca belt of southern British Columbia [ Evenchick et al ., ]. By late Middle to early Late Jurassic time, some hinterland structural styles had switched from southwest to northeast vergent and likely record the cratonward propagation of the retroarc thrust system in Yukon and southeastern British Columbia [e.g., Crowley and Brown , ; Colpron et al ., ; Gibson et al ., , ; Staples et al ., , ]. Peak Barrovian metamorphism associated with this retroarc deformation occurred ~170–160 Ma in southern Omineca belt of British Columbia [e.g., Parrish , ; Evenchick et al ., ], and regional orogenic gold veins that are characteristic of very late to postpeak metamorphic conditions [ Goldfarb and Groves , ] were emplaced into the northern Omineca belt of Yukon by the early Late Jurassic (Figure ) [ Allan et al ., ; Bailey , ].…”

Orogenic pulses in the Alberta Rocky Mountains: Radiometric dating of major faults and comparison with the regional tectono-stratigraphic record

“…5) preserves evidence of penetrative shortening throughout the Late Jurassic to Paleocene (Currie, 1988;Ferguson, 1994;Digel et al, 1998;Reid, 2003;Ghent and Simony, 2005;Gibson et al, 2008). Continued growth of the Omineca highland, as it was translated inboard onto thicker, more rigid crust, loaded the lithosphere and affected the sedimentation patterns of the adjacent basin to the east.…”

A window into the Early to mid‐Cretaceous infrastructure of the Yukon‐Tanana terrane recorded in multi‐stage garnet of west‐central Yukon, Canada

“…Monger et al ., ; Nelson et al ., ; Colpron et al ., ; Beranek & Mortensen, ). In the Mesozoic, the orogen grew as a consequence of protracted compression and crustal thickening during arc‐continent collisions (e.g., Berman et al ., ; Gibson et al ., ) as the North American craton moved westward, converging with its offshore subduction zone (Monger & Price, ). In the southern Canadian Cordillera, a significant body of geochronological data from the metamorphic core of the orogen has revealed that despite similarities in regional metamorphic grade and deformation patterns, both were strongly diachronous, younging systematically with increasing structural depth (Parrish, ).…”

“…Parrish (), Brown () and Gibson et al . () have all attributed this downward younging tectonism in the southeastern Canadian Cordillera to the progressive incorporation and burial of material as the burgeoning orogen propagated northeastward towards the foreland.…”

“…Location abbreviations and references: a, this study and Berman et al . (); b, east‐central Alaska (Pavlis et al ., ; Dusel‐Bacon et al ., ); c, Finlayson region (Murphy, ); d, Shushwap complex (Parrish, ; Crowley et al ., ; Gibson et al ., ); e, Prince Rupert area (Wolf et al ., ).…”