Geochronology of the Canadian Shield in Northeastern Alberta II. Charles–Andrew–Colin Lakes Area

The broad outline of the tectonic–metamorphic history of this area is reasonably clear. Whole rock U–Pb, mineral U–Pb, whole rock Rb–Sr, mineral Rb–Sr, and mineral K–Ar data have resulted in the recognition of a narrow discontinuous N–S zone of Archean (> 2550 m.y.) granitic material which may predate the surrounding widespread migmatitic–gneissic complex. Other N–S belts of younger granitic to dioritic plutons (1900 m.y.) intrude the gneissic complex. A last severe thermal metamorphic event sharply 'reset' mica K–Ar dates for all bodies in the area to 1790 ± 40 m.y. The recently identified Archean belt is located in the Allan fault zone: a complex major zone of weakness which has undergone repeated activation involving deep seated folding, mylonitization, and multiple intrusion, with late plastic deformation and recrystallization of the mylonite belts. The unraveling of the tectonic–metamorphic history of the area is greatly complicated by multiple metamorphic effects and the compositional heterogeneity of the para– and ortho–gneissic materials of the migmatitic–gneissic complex. Local uranium mineralization in this area is geochronologically related to intrusion of the younger granites and is essentially contemporaneous with the main early phase of uranium deposition in the Uranium City area of Saskatchewan.