Intersecting intracontinental Tertiary transform fault systems in the North American Cordillera

Abstract

In central British Columbia, north-trending dextral strike-slip faults that cut Late Eocene granite also truncate northwesttrending dextral strike-slip faults. The northwest-trending strike-slip faults bound the Wolverine Metamorphic Complex (Wolverine Complex), which has been uplifted primarily by northwest-southeast Eocene crustal extension and somewhat by Late Eocene northerly extension. The crustal extension is indicated by shallow-dipping extensions faults, dyke complexes, and stretching lineations. The Wolverine Complex and its bounding faults define a crustal pull-apart in an en echelon dextral transform. The northwest-and north-trending dextral strike-slip faults in central British Columbia are the continuations of faults that transect the interior of the North American Cordillera, and they represent at least two distinct plate boundaries intermittently active during the Early to Middle Eocene, and the Late Eocene to Early Oligocene. Each of these systems consists of en echelon strike-slip faults linked by extensional pull-aparts, locally represented by metamorphic core complexes. These two plate-boundary systems represent two distinct plate-motion configurations between the North American and Kula-Pacific plates. The older plate boundary is truncated and disrupted by the younger one. These two systems may in turn be disrupted by a younger and different plate-motion configuration represented by the transverse Basin and Range extension complex and its northern and southern transform boundary faults.Les failles coulissantes dextres, de direction nord, dans le centre de la Colombie-Britannique, qui coupent les massifs de granite d'bge Cockne tardif, tronquent aussi les failles coulissantes dextres qui sont orientkes nord-ouest. Les failles coulissantes de direction nord-ouest encadrent le Complexe mktamorphique de Wolverine (Complexe de Wolverine), principalement souleve A 1'Eocbne par une extension crustale nord-ouest -sud-est, et partiellement A 1'Eocbne tardif par une extension vers le nord. Les failles de dktachement, les complexes filoniens et les lineations d'ktirement sont les tCmoins de I'extension crustale. Le Complexe de Wolverine et ses failles bordikres definissent un bassin transtension crustal, dCveloppC dans une faille transformante dextre en tchelons. Dans le centre de la Colombie-Britannique, les failles coulissantes dextres de direction nord-ouest et nord representent le prolongement des failles qui transectent I'intCrieur de la Cordillbre de 1'AmCrigue du Nord, et elles indique~t au moins deux bordures distinctes de plaques qui furent Lpisodiquement actives durant 1'Eockne moyen i precoce, et 1'Eockne tardif i I'Oligockne precoce. Chacun de ces systkmes comprend de failles coulissantes en CcheIons relites par des bassins de transtension extensifs, et localement ils correspondent h des noyaux de massifs mktamorphiques. Ces deux systbmes de bordures de plaques reprtsentent deux modes distincts de mouvements entre les plaques de 1'AmCrique du Nord et de Kula -Pacifique. La plus ancienne des b...

Deep seismic reflection constraints on Paleogene crustal extension in the south-central Intermontane belt, British Columbia

“…The dips of mid-crustal reflectors on east-west-oriented lines 10 and 13 are steeper than those observed on north-south lines 5 and 12, and consistent with crustal extension in an approximately westerly direction, although it is not possible to be accurate with so few seismic profiles. West-directed extension would, however, be consistent with the formation of north-striking grabens that could produce the north-trending gravity anomalies, while the northwesttrending gravity anomalies further south may be a consequence of extension under the influence of the Yalakom fault (Struik 1993;Hayward and Calvert 2011).…”

“…1), which ended at ϳ35 Ma (Coleman and Parrish 1991;Umhoefer and Schiarizza 1996). A number of core complexes were also exhumed by normal faulting during the Eocene (Friedman and Armstrong 1988;Struik 1993). From 55 to 45 Ma, a flare-up in volcanic activity resulted in the deposition of mostly felsic to intermediate volcanic and related volcaniclastic rocks of the Ootsa Lake Group across much of the present-day Nechako-Chilcotin plateau (Grainger et al 2001;Bordet et al 2014).…”

Brittle faulting in the Thor–Odin culmination, Monashee complex, southern Canadian Cordillera: constraints on geometry and kinematics

“…Assuming this correlation is correct, the dextral strike-slip displacement on the VCF is 55-60 km. Dextral strike-slip faults of the same age and orientation, with comparable displacements, are reported in the Cariboo Mountains -200 km to the northwest (Struik 1993;McMechan 2000;Reid et al 2002). Gillam (2002), and A. Parmenter (personal communication, 2004).…”

“…The Cariboo Mountains, -200 km northwest of the MC, lie in a possible step-over zone between the continental-scale Northern Rocky Mountain Trench and Fraser River -Straight Creek faults (Price and Carmichael 1986;Struik 1993;McMechan 2000;Reid et al 2002). Struik (1993) describes two episodes of dextral strikeslip faulting in the Pine Pass and McLeod Lake map areas of the Cariboo Mountains (north-south-striking faults cutting earlier northwest-southeast-striking faults). Reid et al (2002) report total dextral strike-slip displacement of 120-200 km in this region.…”

New geophysical models for subsurface velocity structure in the Nechako–Chilcotin plateau from 2.5-D waveform tomography

“…This structure appears to transition abruptly to a low-velocity region at B. Mapping indicates Eocene volcanic rocks that dominate the surficial geology in the southeastern half of the line. Reflectors in the area of B are disrupted adjacent to the high-velocity body at A, and it is likely that the younger material was emplaced in a pull-apart basin during Eocene east-west extension (Struik 1993). The Nazko Cone is visible at C as a high-velocity (ϳ5 km/s) anomaly, due to the presence of basaltic lava that is somewhat faster than Eocene rocks that it unconformably intrudes and overlaps.…”