The Sask Craton and Hearne Province margin: seismic reflection studies in the western Trans-Hudson Orogen

Abstract

A three-dimensional model of the regional crustal architecture of the western Trans-Hudson Orogen, based on the interpretation of 590 km of deep-sounding seismic reflection data and a comparable length of existing seismic reflection information, is presented. The seismic images identify the regional geometry of the basal detachment zone (Pelican thrust) that separates juvenile allochthonous terranes from the underlying Archean microcontinent (Sask craton). The Sask Craton is inferred to have a minimum spatial extent of over 100 000 km2 with an associated crustal root that extends for 200 km along strike. During terminal collision, complete convergence of the Rae–Hearne and Superior continental blocks was precluded by the presence of the Sask Craton, resulting in the preservation of anomalous amounts of oceanic and associated sedimentary juvenile material. Along regional tectonic strike, consistency of crustal structure across the Rae–Hearne margin – Reindeer zone boundary is established. Several phases of tectonic development, including multistage subduction and continent–continent collision, are inferred for the western margin of the orogen. A bright, shallow (2–3.5 s two-way traveltime) band of reflectivity (Wollaston Lake reflector) imaged over ~150 000 km2 area is inferred to be a large post-orogenic mafic intrusion. A highly reflective, well-defined and structurally disturbed Moho discontinuity is mapped throughout the western Trans-Hudson Orogen. The present-day crustal architecture of the western Trans-Hudson Orogen is described in terms of the tectonic evolution within the region.

Crustal anisotropy beneath Hudson Bay from ambient noise tomography: Evidence for post‐orogenic lower‐crustal flow?

“…Continental arc formation due to pre‐collision convergence and ocean‐basin closure is represented by the giant Wathamun‐Chipewyan batholith. Where exposed adjacent to Hudson Bay, the THO contains both juvenile supracrustal domains as well as blocks of pre 1.91 Ga crust, such as the Archean Sask craton [ Hajnal et al , 2005]. The lithospheric mantle beneath Hudson Bay has high shear velocity and is estimated to be at least 200 km in thickness, characteristics that are typical of Archean mantle keels [ Darbyshire and Eaton , 2010].…”

Subhorizontal fabric in exhumed continental lower crust and implications for lower crustal flow: Athabasca granulite terrane, western Canadian Shield

“…These pervasive, gently dipping ductile fabrics represent one plausible explanation for the characteristically high reflectivity and lamellae observed in the lower crustal portions of many deep seismic reflection profiles [e.g., Meissner et al , 2006]. These dramatic reflection patterns have been documented across numerous collisional orogens, including: the Pyrenees, the Himalayas, and the Trans‐Hudson [ Hajnal et al , 2005; Hauck et al , 1998; Ross et al , 2004; Roure et al , 1989]. A fundamental issue in all of the above observations concerns the deformation mechanisms that attend lower crustal flow and the degree to which lower crust partitions strain [e.g., Williams and Jiang , 2005; Williams et al , 2006].…”

“…(a) Simplified geologic map of the western Canadian Shield compiled and modified after Hoffman [1988], Tella et al [2000], Ross [2002], and Hajnal et al [2005]. Note location of Figure 1b at center.…”

Possible role of midcrustal igneous sheet intrusions in cratonic arch formation

“…From crustal‐scale multichannel seismic reflection investigations, instances of anomalously bright midcrustal reflections in otherwise nonreflective crust have been imaged at a number of locations around the world. Because of the strength and character of the reflections and their overall geometries, several of these packages have been interpreted as resulting from dolerite sheets intruded into crystalline basement [e.g., Litak and Hauser , 1992; Mandler and Clowes , 1997; Papasikas and Juhlin , 1997; Ross and Eaton , 1997; Mandler and Clowes , 1998; Hajnal et al , 2005]. Seismically, these sequences are generally characterized by horizontal to subhorizontal discrete bands of bright coherent reflections that extend for tens to hundreds of kilometers and are confined within the mid to upper crust.…”