Abstract

The evolution of the Archean volcanic–plutonic complex in the Kakagi Lake area occurred during a time interval of ca. 32 Ma. The earliest age is graphic from analysis of zircon and baddeleyite in a gabbro intruding the lowermost Katimiagamak Volcanic Group. An age of 2723.2 ± 1.8 Ma on a tonalite gneiss from the interior of the underlying Sabaskong Batholith is indistinguishable from a previously dated massive border phase of the batholith and shows no evidence for inheritance from an older sialic component. An early tonalite phase from the adjacent Aulneau Batholith is dated at graphic, and the latest granodiorite phase is dated at graphic. This defines a time span of about 7 Ma for intrusion of the bulk of the batholith and indicates that previously dated felsic volcanism from the uppermost sequence, above the Kakagi Lake Volcanic Group, is coeval with late plutonic activity in the Aulneau Batholith. The end of regional deformation in the area is given by the ages of two late-tectonic intrusions, the Heronry Lake pluton and the Stephen Lake pluton, dated at 2701.0 ± 1.2 and 2699.2 ± 1.9 Ma, respectively.U–Pb analyses of sphene were carried out on four of the samples in an effort to establish details of the post-folding thermal history of the area. Sphene is least reset in the Heronry Lake pluton (2699.2 ± 1.6 Ma), which is spatially most closely associated with the volcanic rocks and most reset in the Sabaskong gneiss (2673.7 ± 6.6 Ma), the sample most strongly affected by diapirism. The data indicate that regional deformation was a relatively late event, possibly caused by diapirism in the centres of the large batholiths and driven by a long-lived heat source in the mantle or lower crust.

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