Crustal Seismic Signature of the Paleoproterozoic Trans-Hudson Orogen; A Lithoprobe Transect, Canadá

New seismic reflection data collected by UTHOPROBE across the Trans-Hudson Orogen provide striking images of juvenile Paleoproterozoic arc rocks interposed between the deformed margins of the Archean Superior and Hearne cratons. Along the western half of this collisional tectonic belt the crustal architecture is roughly symmetric about a crustal-scale culmination within the accreted juvenile collage, which geological and isotopic data suggest may be cored by Archean basement. West of the culmination, highly reflective packages dip consistently westward into the lower crust, beneath the straddling Wathaman batholith and reworked Archean continental margin of the Hearne craton. On the eastern flank, crustal imbrication on a scale imaged in few other orogens is observed within the juvenile Flin Flon Belt, where a package of shallowly east-dipping reflections extends from the surface to 14 s; sheets of middle to lower crustal arc rocks have been stacked below a major detachment that carries the upper crustal remnants of an island arc complex. Surprisingly, the seismic images show the juvenile arc rocks dipping moderately eastward beneath the craton in contrast to existing tectonic models. The east-dipping reflection fabric, marking Hudsonian tectonic overprint, extends across the Superior Boundary Zone to the Pikwitonei Granulite Belt where upper crustal reflections are west-dipping. An east-dipping boundary between these domains, which soles into the mid-crust, may represent a westverging thrust fault along which the crust of the Archean Superior craton was uplifted. A well-defined Moho, laterally continuous for >500 km, shows considerable relief (38-47 Ion depth), including a prominent root beneath the crustal culmination. The Imaged structures are thought to reflect lateto post-collisional defonnation rather than early subduction polarity.