PALEO-PROTEROZOIC THICK-SKINNED TECTONICS - LITHOPROBE SEISMIC-REFLECTION RESULTS FROM THE EASTERN TRANS-HUDSON OROGEN

New seismic reflection data collected by Lithoprobe across the Trans-H udson Orogen (Manitoba and Saskatchewan) provide striking images of ju venile paleo-Proterozoic arc rocks (Flin Flon and Kisseynew belts) jux taposed against the deformed northwestern margin of the Archean Superi or craton. Crustal imbrication on a scale imaged in few other orogens is observed within the Flin Flon Belt where a package of shallowly eas t-dipping reflections extends from the surface to 14 s. These reflecti ons are attributed to middle to lower crustal arc rocks that appear to have been stacked below a major detachment that underlies the upper c rustal rocks of the Flin Flon Belt. Surprisingly, the seismic images s how the juvenile arc rocks dipping moderately eastward beneath the cra ton in apparent contradiction to existing tectonic models. Geological and geochronological evidence suggest that the observed crustal imbric ation probably reflects late-collisional or postcollisional convergenc e rather than earlier oceanic subduction polarity. The east-dipping re flection fabric, marking a Hudsonian tectonic overprint, extends acros s the Superior Boundary Zone up to the Pikwitonei Granulite Belt where upper crustal reflections are west dipping. An east-dipping seismic b oundary between these domains, which soles into the mid-crust, may rep resent a west-verging thrust fault along which the crust of the Archea n Superior craton was uplifted.