UNRAVELING THE BOUNDARY BETWEEN TURBIDITES OF THE KISSEYNEW BELT AND VOLCANOPLUTONIC ROCKS OF THE FLIN-FLON BELT, TRANS-HUDSON OROGEN, CANADA

The Flin Pion - Kisseynew boundary in the eastern Trans-Hudson Orogen is interpreted here as an early thrust fault that places 1.86-1.84 Ga Kisseynew belt turbidites over previously deformed 1.91-1.88 Ga are an d ocean-floor assemblages of the Flin Pion belt. The basin in which se dimentary rocks of the Kisseynew belt were deposited has been interpre ted to have formed partly within the Flin Pion belt. The fault that ju xtaposes the two belts is interpreted to have been localized near the ancestral basin margin, resulting in development of a major ramp zone during basin closure. This interpreted ramp zone provides an explanati on for the steep to shallow structural transition that corresponds to increasing metamorphic grade. Collapse of the Kisseynew sedimentary ba sin and juxtaposition of the two belts are attributed to southwest-ver ging folding and thrusting that initiated prior to emplacement of 1.83 Ga plutons. This magmatism was followed by regional greenschist- to u pper-amphibolite-grade metamorphism (1.82-1.805 Ga) and renewed southw est-directed folding and thrusting. Late backfolds developed at the le ading edge of the fold-thrust belt. Postpeak metamorphic deformation r esulted in large-scale, upright folding of the fold-thrust stack (incl uding the Flin Pion - Kisseynew boundary). This stage of deformation i s interpreted to record a transition from southwest-directed transport to northwest-southeast-directed shortening at similar to 1.8 Ga.