Stitching together the Ungava Orogen, northern Quebec: geochronological (TIMS and ICP-MS) and geochemical constraints on late magmatic events

Late magmatic activity in the Ungava Orogen of northern Quebec is manifest as granitic dykes and small, rare plutons that crosscut all tectono-stratigraphic elements of the orogen. Conventional U-Pb geochronology (thermal ionization mass spectrometry (TIMS)) on one particularly important pluton that cuts all these domains indicates its age of emplacement at 1742.2 ± 1.3 Ma. This undeformed and nonmetamorphosed pluton postdates the youngest structures in the orogen (D₄ folds), thereby constraining the timing of the latest deformation to >1742 Ma. Laser ablation inductively coupled plasma - mass spectrometry (ICP-MS) on zircons from the same sample identified a large range in ²⁰⁷Pb/²⁰⁶Pb ages of inherited grains from 1.7 to 3.2 Ga, corresponding to the ages of the host rocks for the pluton. It is proposed that anatexis of the surrounding continental crust due to structural thickening during the waning stages of the Ungava orogeny resulted in the generation of the Lac Duquet pluton and was the source for its inherited zircons. -from Authors