The Dorval syenite intrudes quartzofeldspathic gneisses some 35 km southeast of the Grenville Front, between Val d'Or and Montreal. The whole-rock isochron age of 2548 m.y. (initial 87Sr/86Sr ratio of 0.7038) for the syenite stock also establishes the existence of gneissic rocks of Archean derivation at this distance from the Front, and may date the early metamorphism and deformation of these rocks at some time prior to 2550 m.y. ago.

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