Contrasting seismic characteristics of three major faults in northwestern Canada

Abstract

The Lithoprobe Slave -Northern Cordillera Lithospheric Evolution (SNORCLE) profiles crossed three major tectonic zones of the northwestern Canadian Shield and northern Canadian Cordillera that are diverse in age and in depth of penetration. The oldest (2630( -2590, the Yellowknife River fault zone, formed as a strike-slip fault in a tensional strain regime. Reflector attenuation or truncations align vertically beneath the fault trace through much of the crust, implying a near-vertical fault plane. The youngest (60-10 Ma), the Tintina fault zone, produced cumulative dextral strike-slip displacements of 425 km, perhaps 800 km. Tomographic velocity and ray-trace models of reflection data indicate that several fault splays form a tectonic zone 30 km wide at the surface, but truncations of deeper crustal reflections suggest that the zone thins in the mid-crust and widens near the Moho. This apparent variable width versus depth of the Tintina fault is atypical of major strike-slip faults worldwide. The Teslin fault was an active terrane boundary during accretion of terranes onto North America. Observed reflection geometries indicate that the juxtapositions of highly contrasting metamorphic grades across the Teslin fault are confined to the upper crust along SNORCLE line 3, implying that the fault soles eastward into a mid-crustal detachment at the interpreted top of North American crust. The limited depth extent of the Teslin fault zone is similar to some models of the San Andreas fault and may result from their similar histories as convergent margin structures.Résumé : Les profils SNORCLE (la géotraverse de l'évolution lithosphérique de la Cordillère du Nord et du lac des Esclaves) du projet Lithoprobe traversent trois grandes zones tectoniques du nord-ouest du Bouclier canadien et de la Cordillère canadienne du Nord qui ont des âges et des profondeurs de pénétration diverses. La plus vieille zone (2630-2590 Ma), la zone de la faille de la rivière Yellowknife, a été formée en tant que faille décrochante sous un régime de contraintes en tension. Des atténuations ou des troncatures du réflecteur s'alignent verticalement sous la trace de la faille à travers une grande partie de la croûte, impliquant un plan de faille quasi vertical. La zone la plus jeune (60-10 Ma), la zone de la faille Tintina, a produit des déplacements cumulatifs de décrochement dextre de 425 km, voire 800 km. La vitesse tomographique et des modèles de tracé des rayons des données de sismique réflexion indiquent que plusieurs failles mineures divergentes forment une zone tectonique de 30 km de large à la surface mais des réflexions tronquées plus profondes dans la croûte suggèrent que la zone s'amincit à la mi-croûte et s'élargit à proximité du Moho. Cette variation apparente de la largeur par rapport à la profondeur de la faille Tintina est atypique des grandes failles de décrochement à travers le monde. La faille Teslin était une bordure de terrane active durant l'accrétion des terranes à l'Amérique du Nord. Des géométries observées de réflexion ind...

Three-dimensional structure across the Tintina strike-slip fault, northern Canadian Cordillera, from seismic refraction and reflection tomography

“…However, the fact that there appears to be a lower crustal variation associated with the surface trace of the TF in the north and an upper mantle variation associated with the surface trace of the TF in the south, would seem to argue against deeper mantle penetration of the TF in the north. A detailed look at the TF in the reflection data shows that it is much wider and more variable in width in the north compared to the south (Snyder et al 2005). The along‐strike variations of the TF could be due in part to the change in strike direction of the TF between S2 and S3 with more of a westward component in the north (Fig.…”

“…Also, most seismic studies of strike‐slip faults attempt to directly image the fault zone, which our data are unable to do. There are examples of other young and old strike‐slip faults (Stern & McBride 1998) which share one or more of the characteristics of the TF as imaged by the SNORCLE reflection data (Cook et al 2004; Snyder et al 2005): low‐reflectivity, near‐vertical dip angle, average width, variable width, and penetration of the whole crust.…”

“…Although the lithologies may differ somewhat in the two interpretations, the notion of lower crustal continuity across the TF is consistent. Snyder et al (2005) present a detailed analysis of segments of the SNORCLE reflection data across the TF on lines 22 and 31. On line 31, the TF appears to be ∼35 km wide at the surface, 25 km in the mid-crust, and ∼60 km at the Moho.…”

Wandering gravel-bed rivers and high-constructive stable channel sandy fluvial systems in the Ross River area, Yukon Territory, Canada

“…Ledo et al (2000) also recognized a second crustal discontinuity further to the west, which appears to coincide with the St Cyr fault. All of these faults could be linked at depth, as Creaser and Spence (2005) and Snyder et al (2005) indicate that the Tintina fault is a crustal penetrative feature, with brittle faulting on multiple strands in the upper crust over a zone that is w30 km wide. Tempelman-Kluit (1977) provides the most complete coverage of the bedrock geology in the Ross River area.…”

The 3D Geophysical Investigation of a Middle Cretaceous to Paleocene Regional Décollement in the Cordillera of Northern Canada and Alaska

“…Major, NW striking, right‐lateral strike‐slip faults subsequently segmented the northern Cordillera. Interpreted as a steeply NE dipping (Welford et al, ) intracontinental transform fault (Roddick, ), the Tintina fault (Figure ) is associated with a structurally complex ~30‐km wide fault zone (Snyder et al, ). Right‐lateral displacement of dominantly Eocene age (Gabrielse et al, ) is estimated to be ~490 km based on the offset of the Jurassic Inconnu thrust fault (Saltus, ) but only ~430 km based on the offset of the Cretaceous‐aged Tombstone‐Robert Service and Beaver Creek‐White Mountains thrust faults (Gabrielse et al, ).…”