Abstract

The Flin Flon – 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 arc and ocean-floor assemblages of the Flin Flon belt. The basin in which sedimentary rocks of the Kisseynew belt were deposited has been interpreted to have formed partly within the Flin Flon belt. The fault that juxtaposes 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 explanation for the steep to shallow structural transition that corresponds to increasing metamorphic grade. Collapse of the Kisseynew sedimentary basin and juxtaposition of the two belts are attributed to southwest-verging folding and thrusting that initiated prior to emplacement of 1.83 Ga plutons. This magmatism was followed by regional greenschist- to upper-amphibolite-grade metamorphism (1.82–1.805 Ga) and renewed southwest-directed folding and thrusting. Late backfolds developed at the leading edge of the fold-thrust belt. Postpeak metamorphic deformation resulted in large-scale, upright folding of the fold–thrust stack (including the Flin Flon – Kisseynew boundary). This stage of deformation is interpreted to record a transition from southwest-directed transport to northwest-southeast-directed shortening at ~1.8 Ga.

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