Paleo-Proterozoic thick-skinned tectonics: Lithoprobe seismic reflection results from the eastern Trans-Hudson Orogen

Abstract

New seismic reflection data collected by Lithoprobe across the Trans-Hudson Orogen (Manitoba and Saskatchewan) provide striking images of juvenile paleo-Proterozoic arc rocks (Flin Flon and Kisseynew belts) juxtaposed against the deformed northwestern margin of the Archean Superior craton. Crustal imbrication on a scale imaged in few other orogens is observed within the Flin Flon Belt where a package of shallowly east-dipping reflections extends from the surface to 14 s. These reflections are attributed to middle to lower crustal arc rocks that appear to have been stacked below a major detachment that underlies the upper crustal rocks of the Flin Flon Belt. Surprisingly, the seismic images show the juvenile arc rocks dipping moderately eastward beneath the craton in apparent contradiction to existing tectonic models. Geological and geochronological evidence suggest that the observed crustal imbrication probably reflects late-collisional or postcollisional convergence rather than earlier oceanic subduction polarity. The east-dipping reflection fabric, marking a Hudsonian tectonic overprint, extends across the Superior Boundary Zone up to the Pikwitonei Granulite Belt where upper crustal reflections are west dipping. An east-dipping seismic boundary between these domains, which soles into the mid-crust, may represent a west-verging thrust fault along which the crust of the Archean Superior craton was uplifted.

Structural relations between the polydeformed Flin Flon arc assemblage and Missi Group sedimentary rocks, Flin Flon area, Manitoba and Saskatchewan

“…Profiies across the eastern segment of the Reindeer Zone show continuous north-to eastdipping refiectors which extend to the base of the cmst (Lucas et ai., 1993a;White et al, 1994). These observations (cf.…”

“…Seismic transects conducted by LITEOPROBE provide a three-dimensional insight into the nature of the boundaries between the Sask craton basement, the Kisseynew Domain and the Flin Flon Belt, as well as on the major structures that 15 dissect these three areas internally (Lucas et al, 1993aLewry et al, 1994;White et al, 1994). Profiies across the eastern segment of the Reindeer Zone show continuous north-to eastdipping refiectors which extend to the base of the cmst (Lucas et ai., 1993a;White et al, 1994).…”

Electrical-resistivity imaging of the central Trans-Hudson orogen

“…Seismic reflection profiles from the Lithoprobe transect have shown that the internal zone of the THO has been subjected to thick-skinned style deformation with significant dipping reflective zones extending from the surface to Moho depths White et al 1994;Lewry et al 1994). To the west of the Glennie domain, the response is characterized by west-dipping packages of reflectors extending through the crust and within the Glennie domain, and further east, the response is characterized by east-dipping packages (Fig.…”

“…In earlier interpretations of the seismic reflection data, the Sturgeon-Weir shear zone was defined as a moderately steeply dipping east-dipping feature White et al 1994;Hajnal et al 1996). However, the reprocessing of the reflection data by Pandit et al (1998), and particularly the application of a variable cross-dip correction, considerably improved the resolution of some sub-surface features and their correlation with the surface geology (Fig.…”

Magnetic properties and modelling: Lithoprobe seismic reflection line 7C, southern Kisseynew Gneiss Belt, Trans-Hudson Orogen

“…1, 2). Interpretations of the seismic data are described in several papers (e.g., Hajnal et al 1996;Lewry et al 1994;Lucas et al 1993Lucas et al , 1994White et al 1994). The tectonic history of the THO, lasting from about 1900 to 1700 Ma, involved the assemblage and postcollisional deformation of oceanic domains, marginal basins, and a continental margin batholith, having ages in the range 1920-1830 Ma (Ansdell et al 1995;Hajnal et al 1996;Lucas et al 1996).…”