Seismic reflection images of high‐angle faults and linked detachments in the Trans‐Hudson Orogen

Abstract

Postcollisional (1.8–1.7 Ga) intracontinental deformation in the Trans‐Hudson Orogen (Canada) produced a series of orogen‐parallel high‐angle faults and folds. In seismic reflection profiles, the faults are imaged by subvertical zones of diffractions and truncated reflections that extend to 4–8 s (12–24 km). The folded and faulted upper part of the crust is underlain by laterally coherent shallow‐dipping reflections that are locally bounded by discrete, highly reflective zones. These zones are interpreted as detachments (shear zones) and can be traced from the upper to lower crust, where some of them appear to pass into laterally continuous reflections that define the Moho. Two distinct regimes of postcollisional crustal deformation are inferred from the seismic images: high‐angle faulting and lateral block extrusion in the upper crust and low‐angle ductile shearing in the mid/lower crust. The surface geology indicates that the faults resulted in southwest (orogen‐parallel) extrusion of the orogen's internal zone relative to the bounding Archean Hearne and Superior cratons. Faulting was concurrent with the development of upright folds with trends that are subparallel to the extrusion direction. The seismic images suggest that the high‐angle fold/fault structures are kinematically linked to low‐angle detachments represented by laterally coherent, highly reflective zones. The detachment shear zones are inferred to have a top‐to‐the‐southwest sense of shear associated with a subhorizontal, northeast‐southwest extension direction, parallel to those observed for 1.83–1.80 Ga collisional shear zones exposed in major postcollisional fold culminations. Long‐lived orogen‐parallel extension is interpreted as a consequence of the boundary conditions imposed by the northeast trend of both the Superior and Hearne margins.

Electrical-resistivity imaging of the central Trans-Hudson orogen

“…Figure 10a compares the seismic reflectivity and resistivity model in the area of the NACP. The Lithoprobe Vibroseis seismic reflection data in this area are described by and have been analysed in detail by Hajnal et al (1996) and Hajnal et al (2005) to better delineate the tectonic structures. The results of Vibroseis and dynamite surveys are compared by Bezdan and Hajnal (1996), and the Moho has been imaged in using wide-angle reflections by Németh et al.…”

“…Baird and Clowes (1996) suggest that the seismic signature of the Guncoat thrust has a width of around 20 km where it crosses the Lithoprobe transect. Hajnal et al (1996) show the Hartley Shear zone to be a shallow west-dipping structure parallel to the Guncoat thrust and defining the boundary between the Glennie and La Ronge domains. According to the thrust sheet classification of , the Hartley shear zone would represent an internal structure in the Cartier sheet.…”

“…The overlay of the reflectivity and resistivity data sets is based on a seismic velocity of 6 km s -1 . (a) Western part of study area (seismic data from Hajnal et al 1996). Four interpreted locations of the Guncoat thrust are shown: 1, from Hajnal et al (2004); 2, from Lewry et al (1994); 3, from Baird and Clowes (1996); 4, from .…”

“…The eastern La Ronge domain is dominated by high-grade metasedimentary migmatites . The western La Ronge domain consists mainly of low metamorphic grade mafic to felsic metavolcanic rocks and Major geological structures in the study area (after Lewry et al 1994;Hajnal et al 1996). SWSZ, Sturgeon-Weir shear zone; HSZ, Hartley shear zone; SF, Stanley fault; GCT, Guncoat thrust; BRSZ, Birch Rapid "straight belt"; TF, Tabbernor fault; SW, Sahli window; MW, MacMillan Point window; HW, Hunter Bay window; NW, Nistowiak-Iskwatikan window.…”

Petrographie Des Volcanites Et Plutonites De La Partie Sud Du Sillon Volcano-Sedimentaire De Toumodi-Fetekro (Cote D’ivoire)

“…De nombreuses études pétro-structurales, géochronologiques, géochimiques et géophysiques ont montré que le Paléoprotérozoïque est une période charnière dans l'évolution de la croûte terrestre (Barbey et Raith, 1990 ;Lucas et al, 1994 ;Hajnal et al, 1995 ;Vidal et al, 1996 ;Pons et al, 1995 ;Vidal et al, 1996 ;Mortaji et al, 2000). Les caractères archaïques y sont bien marqués, mais de plus en plus d'études révèleraient l'existence d'autres caractères se rapprochant de ceux des chaînes modernes.…”