Protracted Melt-Present Deformation During the Rigolet Phase of the Grenvillian Orogeny. Insights from Geochronology along the Highway 117 Transect Through the Grenville Province in Western Quebec, Canada

In this contribution we use U-Pb zircon geochronology to investigate the age of melt-present deformation within the various structural levels of the Mesoproterozoic Grenville Orogen that are exposed along the Highway 117 transect in western Quebec, Canada. Samples include six syn- to late-deformational felsic leucosomes and injected veins. Four of them are physically linked with hornblende-bearing leucosome in their host gneiss and all six contain undeformed quartz grains, implying they were deformed while still partially molten. Zircon from all samples reveal complex morphologies defined by inherited cores and successions of texturally distinct zones, that mostly share trace element characteristics and yield overlapping Grenvillian 207Pb/206Pb weighted mean ages between ca. 1020-968 Ma. A crustal panel charactered by pervasive migmatites that present evidence for protracted suprasolidus deformation, are key characteristics of channel flow during the youngest phase (Rigolet) of the Grenville Orogen. Field data also indicate that, coeval to deformation in the lower structural level, felsic dykes brecciated mafic components within the upper level; these components were subsequently incorporated into the ductile channel as decametre-sized mafic boudins. Our findings are comparable to recent models advocating Rigolet ductile flow within the Parautochthonous Belt in eastern Quebec but differ from the current conceptual models viewing proposed for the evolution of the orogen during this phase.