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TitrePrecambrian crust beneath the Mesozoic northern Canadian Cordillera discovered by Lithoprobe seismic reflection profiling
AuteurCook, F A; Clowes, R M; Snyder, D B; van der Velden, A J; Hall, K W; Erdmer, P; Evenchick, C A
SourceTectonics vol. 23, TC2010, 2004, 28 pages, (Accès ouvert)
LiensAbstract - Résumé
Séries alt.Commission géologique du Canada, Contributions aux publications extérieures 2002080
Documentpublication en série
Mediapapier; en ligne; numérique
ProvinceAlberta; Colombie-Britannique; Territoires du Nord-Ouest; Yukon
SNRC73M; 74D; 74E; 74L; 74M; 75D; 75E; 75L; 75M; 76D; 83M; 83N; 83O; 83P; 84; 85; 86A; 86B; 86C; 86D; 93M; 93N; 93O; 93P; 94; 95; 96A; 96B; 96C; 96D; 103N; 103O; 103P; 104; 105; 106A; 106B; 106C; 106D; 114; 115A; 115B; 115G; 115H; 115I; 115J; 115O; 115P; 116A; 116B
Lat/Long OENS-140.0000 -110.0000 65.0000 55.0000
Sujetsorogenèse; orogénies; levés de reflexion sismiques; discontinuité de Mohorovicic; évolution tectonique; failles directionnelles; failles, décrochement; zones de failles; études de réflexion; roches magmatiques; roches sédimentaires métamorphosées; géologie du socle; croûte continentale; études de la croûte; evolution de la croûte; craton; tectonique de plaques; terrains; géophysique; pétrologie ignée et métamorphique; sédimentologie; stratigraphie; géologie structurale; tectonique; Mésozoïque; Protérozoïque; Précambrien
Illustrationsgeological sketch maps; location maps; gravity profiles; cross-sections, structural; tables; seismic reflection profiles; cross-sections, stratigraphic
ProgrammeLithoprobe Slave-Northern Cordillera Lithospheric Evolution Transect (SNORCLE)
ProgrammeCRSNG Conseil de recherches en sciences naturelles et en génie du Canada
Diffusé2004 03 30
Résumé(disponible en anglais seulement)
The Cordillera in northern Canada is underlain by westward tapering layers that can be followed from outcrops of Proterozoic strata in the Foreland belt to the lowermost crust of the orogenic interior, a distance of as much as 500 km across strike. They are interpreted as stratified Proterozoic rocks, including \'011.8-0.7 Ga supracrustal rocks and their basement. The layering was discovered on two new deep seismic reflection profiles in the Yukon (Line 3; \'01650 km) and northern British Columbia (Line 2; \'011245 km in two segments) that were acquired as part of the Lithoprobe Slave-Northern Cordillera Lithospheric Evolution (SNORCLE) transect. In the Mackenzie Mountains of the eastern Yukon, the layering in Line 3 is visible between 5.0 and 12.0 s (\'0115 to 36 km depth). It is followed southwestward for nearly 650 km (\'01500 km across strike) and thins to less than 1.0 s (\'013.0-3.5 km thickness) near the Moho at the Yukon-Alaska international boundary. In the northern Rocky Mountains of British Columbia, the upper part of the layering on Line 2 correlates with outcrops of Proterozoic (1.76-1.0 Ga) strata in the Muskwa anticlinorium. At this location, the layering is at least 15 km thick and is followed westward then southward into the middle and lower crust for \'01700 km (\'01300 km across strike). It disappears as a thin taper at the base of the crust \'01150 km east of the coast of the Alaskan panhandle. The only significant disruption in the layering occurs at the Tintina fault zone, a late to postorogenic strike-slip fault with up to 800 km of displacement, which appears as a vertical zone of little reflectivity that disrupts the continuity of the deep layering on both profiles (\'01300 km apart). The base of the layered reflection zone coincides with the Moho, which exhibits variable character and undulates in a series of broad arches with widths of \'01150 km. In general, the mantle appears to have few reflections. However, at the southwest end of Line 3 near the Alaska-British Columbia border, a reflection dips eastward from \'0114.0 s to \'0121.0 s (\'0145 to 73 km depth) beneath exposed Eocene magmatic rocks. It is interpreted as a relict subduction surface of the Kula plate. Our interpretation of Proterozoic layered rocks beneath most of the northern Cordillera suggests a much different crustal structure than previously considered: (1) Ancient North American crust comprising up to 25 km of metamorphosed Proterozoic to Paleozoic sediments plus 5-10 km of pre-1.8 Ga crystalline basement projects westward beneath most of the northern Canadian Cordillera. (2) The lateral (500 km by at least 1000 km) and vertical (up to 25 km) extent of the Proterozoic layers and their internal deformation are consistent with a long-lived margin for northwestern North America with alternating episodes of extension and contraction. (3) The detachments that carry deformed rocks of the Mackenzie Mountains and northern Rocky Mountains are largely confined to the upper crustal region above the layering. (4) Accreted terranes include thin klippen that were thrust over North American pericratonic strata (e.g., Yukon-Tanana), and terranes such as Nisling and Stikinia that thicken westward as the underlying Proterozoic layers taper and disappear. (5) The ages of exposed rocks are not necessarily indicative of the ages of underlying crust, a frequent observation in Lithoprobe interpretations, so that estimates of crustal growth based on surface geology may not be representative.