Vertical incidence seismic data were collected along a 300 km-long profile across the northwestern flank of the Trans-Hudson Orogen in Saskatchewan (line S2b). The present study integrates the seismic data with previously published geological maps and recent results from the La Ronge – Lynn Lake Bridge Project that provide new constraints on the lithological, structural, and tectonic framework of this collisional zone. An interpretative section, based on the seismic reflectivity and surface geological constraints, is presented. The integrated data suggest the following key elements. (1) Although an early foreland-vergent accretion history is suggested by surficial geological constraints, the predominant fabric is reflected by penetrative hinterlandward vergence. (2) A zone of more reflective lower crust with hinterland-verging fabric may represent "fossil" reflectors from a pre-collisional accretionary phase. (3) The Archean to Paleoproterozoic Sask Craton may extend in the lower middle crust to at least beneath Rottenstone Domain, consistent with what is observed along strike on other Lithoprobe seismic profiles. (4) The Needle Falls and Parker Lake shear zones do not appear to be associated with obvious reflectors, consistent with observations from Reindeer Lake, suggesting that they merely rework the Wathaman Batholith intrusive margin and are not fundamental sutures. (5) The La Ronge and Rottenstone domains show nearly identical seismic properties, consistent with recent mapping results in the Reindeer Lake area that suggest that they are temporally and, at least in part, lithologically related in the area covered by, and to the east of, seismic line S2b.

A summary and comparison of geophysical data and models for the Trans-Hudson Orogen in northern Manitoba and Saskatchewan are presented. Magnetic total field and Bouguer gravity maps are used to define the along-strike extension of geological domains of the orogen exposed on the Canadian Shield, and a two-dimensional density model is produced, which accounts for the observed variations of the Bouguer gravity field across the orogen. An 800-km-long crustal section across the entire continent–continent collision zone, including the edges of the bounding cratonic blocks, is presented. It incorporates seismic reflectivity, seismic velocities, resistivity, and density models. Key results include (1) evidence for west-vergent crustal stacking and exhumation in the eastern Trans-Hudson Orogen in the form of preserved Moho topography and the presence of higher grade (higher velocity) rocks in the hanging wall of an east-dipping crustal stack; (2) definition of the eastward extent of the Archean Sask craton in the subsurface based on distinct lower crustal properties; and (3) 400 m of present-day surface topography and 6–8 km of relief on the Moho are isostatically compensated mainly within the upper mantle by a westward increase in upper mantle temperatures by 40–155 °C and (or) 16–107 km of thinning of the mantle lithosphere.

The Trans-Hudson Orogen (THO) is the world's largest Paleoproterozoic orogenic belt. Data from three refraction profiles are used to investigate its lithospheric structure in Saskatchewan and Manitoba. R1 crosses the orogen from the Hearne craton on the west to the Superior craton on the east; R2 and R3 are along the orogen. P-wave velocity structural models are generated using a ray-based technique. On line R1, higher crustal velocities in its eastern part coincide with rocks of the Flin Flon – Namew gneiss complex. Depth to Moho is in the 40–45 km range and equates to that from the reflection data, including a small crustal root below the Sask minicontinent. Along lines R2 and R3, depth to Moho varies from about 40 km up to 55 km at the north end of R2 and south end of R3. In general, variations in crustal velocity and depth to Moho do not correlate with the location and extent of geological domains; they appear to reflect the complex deformation and metamorphic history of the crustal rocks. Mantle velocities are high, ~8.2 km/s. However a limited area shows prominent velocity anisotropy, with values of 8.6 km/s along R2 and R3 and 8.1 km/s along R1. We speculate that the observed anisotropy represents an ~100-km-wide mantle suture zone resulting from the collision of Archean plates. The suture zone accommodated limited extensional deformation, associated with a counterclockwise rotation of the Superior plate, to generate the anisotropy. In this model, the lithospheric mantle of the THO internal domains and Sask craton are detached.

No abstract

No abstract